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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  linux/fs/buffer.c
  *
  *  Copyright (C) 1991, 1992, 2002  Linus Torvalds
  */
 
 /*
  * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
  *
  * Removed a lot of unnecessary code and simplified things now that
  * the buffer cache isn't our primary cache - Andrew Tridgell 12/96
  *
  * Speed up hash, lru, and free list operations.  Use gfp() for allocating
  * hash table, use SLAB cache for buffer heads. SMP threading.  -DaveM
  *
  * Added 32k buffer block sizes - these are required older ARM systems. - RMK
  *
  * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
  */
 
 #include <linux/kernel.h>
 #include <linux/sched/signal.h>
 #include <linux/syscalls.h>
 #include <linux/fs.h>
 #include <linux/iomap.h>
 #include <linux/mm.h>
 #include <linux/percpu.h>
 #include <linux/slab.h>
 #include <linux/capability.h>
 #include <linux/blkdev.h>
 #include <linux/file.h>
 #include <linux/quotaops.h>
 #include <linux/highmem.h>
 #include <linux/export.h>
 #include <linux/backing-dev.h>
 #include <linux/writeback.h>
 #include <linux/hash.h>
 #include <linux/suspend.h>
 #include <linux/buffer_head.h>
 #include <linux/task_io_accounting_ops.h>
 #include <linux/bio.h>
 #include <linux/cpu.h>
 #include <linux/bitops.h>
 #include <linux/mpage.h>
 #include <linux/bit_spinlock.h>
 #include <linux/pagevec.h>
 #include <linux/sched/mm.h>
 #include <trace/events/block.h>
 #include <linux/fscrypt.h>
 
 #include "internal.h"
 
 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
 static int submit_bh_wbc(blk_opf_t opf, struct buffer_head *bh,
              struct writeback_control *wbc);
 
 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
 
 inline void touch_buffer(struct buffer_head *bh)
 {
     trace_block_touch_buffer(bh);
     mark_page_accessed(bh->b_page);
 }
 EXPORT_SYMBOL(touch_buffer);
 
 void __lock_buffer(struct buffer_head *bh)
 {
     wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(__lock_buffer);
 
 void unlock_buffer(struct buffer_head *bh)
 {
     clear_bit_unlock(BH_Lock, &bh->b_state);
     smp_mb__after_atomic();
     wake_up_bit(&bh->b_state, BH_Lock);
 }
 EXPORT_SYMBOL(unlock_buffer);
 
 /*
  * Returns if the folio has dirty or writeback buffers. If all the buffers
  * are unlocked and clean then the folio_test_dirty information is stale. If
  * any of the buffers are locked, it is assumed they are locked for IO.
  */
 void buffer_check_dirty_writeback(struct folio *folio,
                      bool *dirty, bool *writeback)
 {
     struct buffer_head *head, *bh;
     *dirty = false;
     *writeback = false;
 
     BUG_ON(!folio_test_locked(folio));
 
     head = folio_buffers(folio);
     if (!head)
         return;
 
     if (folio_test_writeback(folio))
         *writeback = true;
 
     bh = head;
     do {
         if (buffer_locked(bh))
             *writeback = true;
 
         if (buffer_dirty(bh))
             *dirty = true;
 
         bh = bh->b_this_page;
     } while (bh != head);
 }
 EXPORT_SYMBOL(buffer_check_dirty_writeback);
 
 /*
  * Block until a buffer comes unlocked.  This doesn't stop it
  * from becoming locked again - you have to lock it yourself
  * if you want to preserve its state.
  */
 void __wait_on_buffer(struct buffer_head * bh)
 {
     wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(__wait_on_buffer);
 
 static void buffer_io_error(struct buffer_head *bh, char *msg)
 {
     if (!test_bit(BH_Quiet, &bh->b_state))
         printk_ratelimited(KERN_ERR
             "Buffer I/O error on dev %pg, logical block %llu%s\n",
             bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
 }
 
 /*
  * End-of-IO handler helper function which does not touch the bh after
  * unlocking it.
  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
  * a race there is benign: unlock_buffer() only use the bh's address for
  * hashing after unlocking the buffer, so it doesn't actually touch the bh
  * itself.
  */
 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
 {
     if (uptodate) {
         set_buffer_uptodate(bh);
     } else {
         /* This happens, due to failed read-ahead attempts. */
         clear_buffer_uptodate(bh);
     }
     unlock_buffer(bh);
 }
 
 /*
  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
  * unlock the buffer. This is what ll_rw_block uses too.
  */
 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
 {
     __end_buffer_read_notouch(bh, uptodate);
     put_bh(bh);
 }
 EXPORT_SYMBOL(end_buffer_read_sync);
 
 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 {
     if (uptodate) {
         set_buffer_uptodate(bh);
     } else {
         buffer_io_error(bh, ", lost sync page write");
         mark_buffer_write_io_error(bh);
         clear_buffer_uptodate(bh);
     }
     unlock_buffer(bh);
     put_bh(bh);
 }
 EXPORT_SYMBOL(end_buffer_write_sync);
 
 /*
  * Various filesystems appear to want __find_get_block to be non-blocking.
  * But it's the page lock which protects the buffers.  To get around this,
  * we get exclusion from try_to_free_buffers with the blockdev mapping's
  * private_lock.
  *
  * Hack idea: for the blockdev mapping, private_lock contention
  * may be quite high.  This code could TryLock the page, and if that
  * succeeds, there is no need to take private_lock.
  */
 static struct buffer_head *
 __find_get_block_slow(struct block_device *bdev, sector_t block)
 {
     struct inode *bd_inode = bdev->bd_inode;
     struct address_space *bd_mapping = bd_inode->i_mapping;
     struct buffer_head *ret = NULL;
     pgoff_t index;
     struct buffer_head *bh;
     struct buffer_head *head;
     struct page *page;
     int all_mapped = 1;
     static DEFINE_RATELIMIT_STATE(last_warned, HZ, 1);
 
     index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
     page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
     if (!page)
         goto out;
 
     spin_lock(&bd_mapping->private_lock);
     if (!page_has_buffers(page))
         goto out_unlock;
     head = page_buffers(page);
     bh = head;
     do {
         if (!buffer_mapped(bh))
             all_mapped = 0;
         else if (bh->b_blocknr == block) {
             ret = bh;
             get_bh(bh);
             goto out_unlock;
         }
         bh = bh->b_this_page;
     } while (bh != head);
 
     /* we might be here because some of the buffers on this page are
      * not mapped.  This is due to various races between
      * file io on the block device and getblk.  It gets dealt with
      * elsewhere, don't buffer_error if we had some unmapped buffers
      */
     ratelimit_set_flags(&last_warned, RATELIMIT_MSG_ON_RELEASE);
     if (all_mapped && __ratelimit(&last_warned)) {
         printk("__find_get_block_slow() failed. block=%llu, "
                "b_blocknr=%llu, b_state=0x%08lx, b_size=%zu, "
                "device %pg blocksize: %d\n",
                (unsigned long long)block,
                (unsigned long long)bh->b_blocknr,
                bh->b_state, bh->b_size, bdev,
                1 << bd_inode->i_blkbits);
     }
 out_unlock:
     spin_unlock(&bd_mapping->private_lock);
     put_page(page);
 out:
     return ret;
 }
 
 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
 {
     unsigned long flags;
     struct buffer_head *first;
     struct buffer_head *tmp;
     struct page *page;
     int page_uptodate = 1;
 
     BUG_ON(!buffer_async_read(bh));
 
     page = bh->b_page;
     if (uptodate) {
         set_buffer_uptodate(bh);
     } else {
         clear_buffer_uptodate(bh);
         buffer_io_error(bh, ", async page read");
         SetPageError(page);
     }
 
     /*
      * Be _very_ careful from here on. Bad things can happen if
      * two buffer heads end IO at almost the same time and both
      * decide that the page is now completely done.
      */
     first = page_buffers(page);
     spin_lock_irqsave(&first->b_uptodate_lock, flags);
     clear_buffer_async_read(bh);
     unlock_buffer(bh);
     tmp = bh;
     do {
         if (!buffer_uptodate(tmp))
             page_uptodate = 0;
         if (buffer_async_read(tmp)) {
             BUG_ON(!buffer_locked(tmp));
             goto still_busy;
         }
         tmp = tmp->b_this_page;
     } while (tmp != bh);
     spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
 
     /*
      * If all of the buffers are uptodate then we can set the page
      * uptodate.
      */
     if (page_uptodate)
         SetPageUptodate(page);
     unlock_page(page);
     return;
 
 still_busy:
     spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
     return;
 }
 
 struct decrypt_bh_ctx {
     struct work_struct work;
     struct buffer_head *bh;
 };
 
 static void decrypt_bh(struct work_struct *work)
 {
     struct decrypt_bh_ctx *ctx =
         container_of(work, struct decrypt_bh_ctx, work);
     struct buffer_head *bh = ctx->bh;
     int err;
 
     err = fscrypt_decrypt_pagecache_blocks(bh->b_page, bh->b_size,
                            bh_offset(bh));
     end_buffer_async_read(bh, err == 0);
     kfree(ctx);
 }
 
 /*
  * I/O completion handler for block_read_full_folio() - pages
  * which come unlocked at the end of I/O.
  */
 static void end_buffer_async_read_io(struct buffer_head *bh, int uptodate)
 {
     /* Decrypt if needed */
     if (uptodate &&
         fscrypt_inode_uses_fs_layer_crypto(bh->b_page->mapping->host)) {
         struct decrypt_bh_ctx *ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
 
         if (ctx) {
             INIT_WORK(&ctx->work, decrypt_bh);
             ctx->bh = bh;
             fscrypt_enqueue_decrypt_work(&ctx->work);
             return;
         }
         uptodate = 0;
     }
     end_buffer_async_read(bh, uptodate);
 }
 
 /*
  * Completion handler for block_write_full_page() - pages which are unlocked
  * during I/O, and which have PageWriteback cleared upon I/O completion.
  */
 void end_buffer_async_write(struct buffer_head *bh, int uptodate)
 {
     unsigned long flags;
     struct buffer_head *first;
     struct buffer_head *tmp;
     struct page *page;
 
     BUG_ON(!buffer_async_write(bh));
 
     page = bh->b_page;
     if (uptodate) {
         set_buffer_uptodate(bh);
     } else {
         buffer_io_error(bh, ", lost async page write");
         mark_buffer_write_io_error(bh);
         clear_buffer_uptodate(bh);
         SetPageError(page);
     }
 
     first = page_buffers(page);
     spin_lock_irqsave(&first->b_uptodate_lock, flags);
 
     clear_buffer_async_write(bh);
     unlock_buffer(bh);
     tmp = bh->b_this_page;
     while (tmp != bh) {
         if (buffer_async_write(tmp)) {
             BUG_ON(!buffer_locked(tmp));
             goto still_busy;
         }
         tmp = tmp->b_this_page;
     }
     spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
     end_page_writeback(page);
     return;
 
 still_busy:
     spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
     return;
 }
 EXPORT_SYMBOL(end_buffer_async_write);
 
 /*
  * If a page's buffers are under async readin (end_buffer_async_read
  * completion) then there is a possibility that another thread of
  * control could lock one of the buffers after it has completed
  * but while some of the other buffers have not completed.  This
  * locked buffer would confuse end_buffer_async_read() into not unlocking
  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
  * that this buffer is not under async I/O.
  *
  * The page comes unlocked when it has no locked buffer_async buffers
  * left.
  *
  * PageLocked prevents anyone starting new async I/O reads any of
  * the buffers.
  *
  * PageWriteback is used to prevent simultaneous writeout of the same
  * page.
  *
  * PageLocked prevents anyone from starting writeback of a page which is
  * under read I/O (PageWriteback is only ever set against a locked page).
  */
 static void mark_buffer_async_read(struct buffer_head *bh)
 {
     bh->b_end_io = end_buffer_async_read_io;
     set_buffer_async_read(bh);
 }
 
 static void mark_buffer_async_write_endio(struct buffer_head *bh,
                       bh_end_io_t *handler)
 {
     bh->b_end_io = handler;
     set_buffer_async_write(bh);
 }
 
 void mark_buffer_async_write(struct buffer_head *bh)
 {
     mark_buffer_async_write_endio(bh, end_buffer_async_write);
 }
 EXPORT_SYMBOL(mark_buffer_async_write);
 
 
 /*
  * fs/buffer.c contains helper functions for buffer-backed address space's
  * fsync functions.  A common requirement for buffer-based filesystems is
  * that certain data from the backing blockdev needs to be written out for
  * a successful fsync().  For example, ext2 indirect blocks need to be
  * written back and waited upon before fsync() returns.
  *
  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
  * management of a list of dependent buffers at ->i_mapping->private_list.
  *
  * Locking is a little subtle: try_to_free_buffers() will remove buffers
  * from their controlling inode's queue when they are being freed.  But
  * try_to_free_buffers() will be operating against the *blockdev* mapping
  * at the time, not against the S_ISREG file which depends on those buffers.
  * So the locking for private_list is via the private_lock in the address_space
  * which backs the buffers.  Which is different from the address_space 
  * against which the buffers are listed.  So for a particular address_space,
  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
  * mapping->private_list will always be protected by the backing blockdev's
  * ->private_lock.
  *
  * Which introduces a requirement: all buffers on an address_space's
  * ->private_list must be from the same address_space: the blockdev's.
  *
  * address_spaces which do not place buffers at ->private_list via these
  * utility functions are free to use private_lock and private_list for
  * whatever they want.  The only requirement is that list_empty(private_list)
  * be true at clear_inode() time.
  *
  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
  * filesystems should do that.  invalidate_inode_buffers() should just go
  * BUG_ON(!list_empty).
  *
  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
  * take an address_space, not an inode.  And it should be called
  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
  * queued up.
  *
  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
  * list if it is already on a list.  Because if the buffer is on a list,
  * it *must* already be on the right one.  If not, the filesystem is being
  * silly.  This will save a ton of locking.  But first we have to ensure
  * that buffers are taken *off* the old inode's list when they are freed
  * (presumably in truncate).  That requires careful auditing of all
  * filesystems (do it inside bforget()).  It could also be done by bringing
  * b_inode back.
  */
 
 /*
  * The buffer's backing address_space's private_lock must be held
  */
 static void __remove_assoc_queue(struct buffer_head *bh)
 {
     list_del_init(&bh->b_assoc_buffers);
     WARN_ON(!bh->b_assoc_map);
     bh->b_assoc_map = NULL;
 }
 
 int inode_has_buffers(struct inode *inode)
 {
     return !list_empty(&inode->i_data.private_list);
 }
 
 /*
  * osync is designed to support O_SYNC io.  It waits synchronously for
  * all already-submitted IO to complete, but does not queue any new
  * writes to the disk.
  *
  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
  * you dirty the buffers, and then use osync_inode_buffers to wait for
  * completion.  Any other dirty buffers which are not yet queued for
  * write will not be flushed to disk by the osync.
  */
 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 {
     struct buffer_head *bh;
     struct list_head *p;
     int err = 0;
 
     spin_lock(lock);
 repeat:
     list_for_each_prev(p, list) {
         bh = BH_ENTRY(p);
         if (buffer_locked(bh)) {
             get_bh(bh);
             spin_unlock(lock);
             wait_on_buffer(bh);
             if (!buffer_uptodate(bh))
                 err = -EIO;
             brelse(bh);
             spin_lock(lock);
             goto repeat;
         }
     }
     spin_unlock(lock);
     return err;
 }
 
 void emergency_thaw_bdev(struct super_block *sb)
 {
     while (sb->s_bdev && !thaw_bdev(sb->s_bdev))
         printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
 }
 
 /**
  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
  * @mapping: the mapping which wants those buffers written
  *
  * Starts I/O against the buffers at mapping->private_list, and waits upon
  * that I/O.
  *
  * Basically, this is a convenience function for fsync().
  * @mapping is a file or directory which needs those buffers to be written for
  * a successful fsync().
  */
 int sync_mapping_buffers(struct address_space *mapping)
 {
     struct address_space *buffer_mapping = mapping->private_data;
 
     if (buffer_mapping == NULL || list_empty(&mapping->private_list))
         return 0;
 
     return fsync_buffers_list(&buffer_mapping->private_lock,
                     &mapping->private_list);
 }
 EXPORT_SYMBOL(sync_mapping_buffers);
 
 /*
  * Called when we've recently written block `bblock', and it is known that
  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
  */
 void write_boundary_block(struct block_device *bdev,
             sector_t bblock, unsigned blocksize)
 {
     struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
     if (bh) {
         if (buffer_dirty(bh))
             ll_rw_block(REQ_OP_WRITE, 1, &bh);
         put_bh(bh);
     }
 }
 
 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
 {
     struct address_space *mapping = inode->i_mapping;
     struct address_space *buffer_mapping = bh->b_page->mapping;
 
     mark_buffer_dirty(bh);
     if (!mapping->private_data) {
         mapping->private_data = buffer_mapping;
     } else {
         BUG_ON(mapping->private_data != buffer_mapping);
     }
     if (!bh->b_assoc_map) {
         spin_lock(&buffer_mapping->private_lock);
         list_move_tail(&bh->b_assoc_buffers,
                 &mapping->private_list);
         bh->b_assoc_map = mapping;
         spin_unlock(&buffer_mapping->private_lock);
     }
 }
 EXPORT_SYMBOL(mark_buffer_dirty_inode);
 
 /*
  * Add a page to the dirty page list.
  *
  * It is a sad fact of life that this function is called from several places
  * deeply under spinlocking.  It may not sleep.
  *
  * If the page has buffers, the uptodate buffers are set dirty, to preserve
  * dirty-state coherency between the page and the buffers.  It the page does
  * not have buffers then when they are later attached they will all be set
  * dirty.
  *
  * The buffers are dirtied before the page is dirtied.  There's a small race
  * window in which a writepage caller may see the page cleanness but not the
  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
  * before the buffers, a concurrent writepage caller could clear the page dirty
  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
  * page on the dirty page list.
  *
  * We use private_lock to lock against try_to_free_buffers while using the
  * page's buffer list.  Also use this to protect against clean buffers being
  * added to the page after it was set dirty.
  *
  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
  * address_space though.
  */
 bool block_dirty_folio(struct address_space *mapping, struct folio *folio)
 {
     struct buffer_head *head;
     bool newly_dirty;
 
     spin_lock(&mapping->private_lock);
     head = folio_buffers(folio);
     if (head) {
         struct buffer_head *bh = head;
 
         do {
             set_buffer_dirty(bh);
             bh = bh->b_this_page;
         } while (bh != head);
     }
     /*
      * Lock out page's memcg migration to keep PageDirty
      * synchronized with per-memcg dirty page counters.
      */
     folio_memcg_lock(folio);
     newly_dirty = !folio_test_set_dirty(folio);
     spin_unlock(&mapping->private_lock);
 
     if (newly_dirty)
         __folio_mark_dirty(folio, mapping, 1);
 
     folio_memcg_unlock(folio);
 
     if (newly_dirty)
         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 
     return newly_dirty;
 }
 EXPORT_SYMBOL(block_dirty_folio);
 
 /*
  * Write out and wait upon a list of buffers.
  *
  * We have conflicting pressures: we want to make sure that all
  * initially dirty buffers get waited on, but that any subsequently
  * dirtied buffers don't.  After all, we don't want fsync to last
  * forever if somebody is actively writing to the file.
  *
  * Do this in two main stages: first we copy dirty buffers to a
  * temporary inode list, queueing the writes as we go.  Then we clean
  * up, waiting for those writes to complete.
  * 
  * During this second stage, any subsequent updates to the file may end
  * up refiling the buffer on the original inode's dirty list again, so
  * there is a chance we will end up with a buffer queued for write but
  * not yet completed on that list.  So, as a final cleanup we go through
  * the osync code to catch these locked, dirty buffers without requeuing
  * any newly dirty buffers for write.
  */
 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
 {
     struct buffer_head *bh;
     struct list_head tmp;
     struct address_space *mapping;
     int err = 0, err2;
     struct blk_plug plug;
 
     INIT_LIST_HEAD(&tmp);
     blk_start_plug(&plug);
 
     spin_lock(lock);
     while (!list_empty(list)) {
         bh = BH_ENTRY(list->next);
         mapping = bh->b_assoc_map;
         __remove_assoc_queue(bh);
         /* Avoid race with mark_buffer_dirty_inode() which does
          * a lockless check and we rely on seeing the dirty bit */
         smp_mb();
         if (buffer_dirty(bh) || buffer_locked(bh)) {
             list_add(&bh->b_assoc_buffers, &tmp);
             bh->b_assoc_map = mapping;
             if (buffer_dirty(bh)) {
                 get_bh(bh);
                 spin_unlock(lock);
                 /*
                  * Ensure any pending I/O completes so that
                  * write_dirty_buffer() actually writes the
                  * current contents - it is a noop if I/O is
                  * still in flight on potentially older
                  * contents.
                  */
                 write_dirty_buffer(bh, REQ_SYNC);
 
                 /*
                  * Kick off IO for the previous mapping. Note
                  * that we will not run the very last mapping,
                  * wait_on_buffer() will do that for us
                  * through sync_buffer().
                  */
                 brelse(bh);
                 spin_lock(lock);
             }
         }
     }
 
     spin_unlock(lock);
     blk_finish_plug(&plug);
     spin_lock(lock);
 
     while (!list_empty(&tmp)) {
         bh = BH_ENTRY(tmp.prev);
         get_bh(bh);
         mapping = bh->b_assoc_map;
         __remove_assoc_queue(bh);
         /* Avoid race with mark_buffer_dirty_inode() which does
          * a lockless check and we rely on seeing the dirty bit */
         smp_mb();
         if (buffer_dirty(bh)) {
             list_add(&bh->b_assoc_buffers,
                  &mapping->private_list);
             bh->b_assoc_map = mapping;
         }
         spin_unlock(lock);
         wait_on_buffer(bh);
         if (!buffer_uptodate(bh))
             err = -EIO;
         brelse(bh);
         spin_lock(lock);
     }
     
     spin_unlock(lock);
     err2 = osync_buffers_list(lock, list);
     if (err)
         return err;
     else
         return err2;
 }
 
 /*
  * Invalidate any and all dirty buffers on a given inode.  We are
  * probably unmounting the fs, but that doesn't mean we have already
  * done a sync().  Just drop the buffers from the inode list.
  *
  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
  * assumes that all the buffers are against the blockdev.  Not true
  * for reiserfs.
  */
 void invalidate_inode_buffers(struct inode *inode)
 {
     if (inode_has_buffers(inode)) {
         struct address_space *mapping = &inode->i_data;
         struct list_head *list = &mapping->private_list;
         struct address_space *buffer_mapping = mapping->private_data;
 
         spin_lock(&buffer_mapping->private_lock);
         while (!list_empty(list))
             __remove_assoc_queue(BH_ENTRY(list->next));
         spin_unlock(&buffer_mapping->private_lock);
     }
 }
 EXPORT_SYMBOL(invalidate_inode_buffers);
 
 /*
  * Remove any clean buffers from the inode's buffer list.  This is called
  * when we're trying to free the inode itself.  Those buffers can pin it.
  *
  * Returns true if all buffers were removed.
  */
 int remove_inode_buffers(struct inode *inode)
 {
     int ret = 1;
 
     if (inode_has_buffers(inode)) {
         struct address_space *mapping = &inode->i_data;
         struct list_head *list = &mapping->private_list;
         struct address_space *buffer_mapping = mapping->private_data;
 
         spin_lock(&buffer_mapping->private_lock);
         while (!list_empty(list)) {
             struct buffer_head *bh = BH_ENTRY(list->next);
             if (buffer_dirty(bh)) {
                 ret = 0;
                 break;
             }
             __remove_assoc_queue(bh);
         }
         spin_unlock(&buffer_mapping->private_lock);
     }
     return ret;
 }
 
 /*
  * Create the appropriate buffers when given a page for data area and
  * the size of each buffer.. Use the bh->b_this_page linked list to
  * follow the buffers created.  Return NULL if unable to create more
  * buffers.
  *
  * The retry flag is used to differentiate async IO (paging, swapping)
  * which may not fail from ordinary buffer allocations.
  */
 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
         bool retry)
 {
     struct buffer_head *bh, *head;
     gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
     long offset;
     struct mem_cgroup *memcg, *old_memcg;
 
     if (retry)
         gfp |= __GFP_NOFAIL;
 
     /* The page lock pins the memcg */
     memcg = page_memcg(page);
     old_memcg = set_active_memcg(memcg);
 
     head = NULL;
     offset = PAGE_SIZE;
     while ((offset -= size) >= 0) {
         bh = alloc_buffer_head(gfp);
         if (!bh)
             goto no_grow;
 
         bh->b_this_page = head;
         bh->b_blocknr = -1;
         head = bh;
 
         bh->b_size = size;
 
         /* Link the buffer to its page */
         set_bh_page(bh, page, offset);
     }
 out:
     set_active_memcg(old_memcg);
     return head;
 /*
  * In case anything failed, we just free everything we got.
  */
 no_grow:
     if (head) {
         do {
             bh = head;
             head = head->b_this_page;
             free_buffer_head(bh);
         } while (head);
     }
 
     goto out;
 }
 EXPORT_SYMBOL_GPL(alloc_page_buffers);
 
 static inline void
 link_dev_buffers(struct page *page, struct buffer_head *head)
 {
     struct buffer_head *bh, *tail;
 
     bh = head;
     do {
         tail = bh;
         bh = bh->b_this_page;
     } while (bh);
     tail->b_this_page = head;
     attach_page_private(page, head);
 }
 
 static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
 {
     sector_t retval = ~((sector_t)0);
     loff_t sz = bdev_nr_bytes(bdev);
 
     if (sz) {
         unsigned int sizebits = blksize_bits(size);
         retval = (sz >> sizebits);
     }
     return retval;
 }
 
 /*
  * Initialise the state of a blockdev page's buffers.
  */ 
 static sector_t
 init_page_buffers(struct page *page, struct block_device *bdev,
             sector_t block, int size)
 {
     struct buffer_head *head = page_buffers(page);
     struct buffer_head *bh = head;
     int uptodate = PageUptodate(page);
     sector_t end_block = blkdev_max_block(bdev, size);
 
     do {
         if (!buffer_mapped(bh)) {
             bh->b_end_io = NULL;
             bh->b_private = NULL;
             bh->b_bdev = bdev;
             bh->b_blocknr = block;
             if (uptodate)
                 set_buffer_uptodate(bh);
             if (block < end_block)
                 set_buffer_mapped(bh);
         }
         block++;
         bh = bh->b_this_page;
     } while (bh != head);
 
     /*
      * Caller needs to validate requested block against end of device.
      */
     return end_block;
 }
 
 /*
  * Create the page-cache page that contains the requested block.
  *
  * This is used purely for blockdev mappings.
  */
 static int
 grow_dev_page(struct block_device *bdev, sector_t block,
           pgoff_t index, int size, int sizebits, gfp_t gfp)
 {
     struct inode *inode = bdev->bd_inode;
     struct page *page;
     struct buffer_head *bh;
     sector_t end_block;
     int ret = 0;
     gfp_t gfp_mask;
 
     gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
 
     /*
      * XXX: __getblk_slow() can not really deal with failure and
      * will endlessly loop on improvised global reclaim.  Prefer
      * looping in the allocator rather than here, at least that
      * code knows what it's doing.
      */
     gfp_mask |= __GFP_NOFAIL;
 
     page = find_or_create_page(inode->i_mapping, index, gfp_mask);
 
     BUG_ON(!PageLocked(page));
 
     if (page_has_buffers(page)) {
         bh = page_buffers(page);
         if (bh->b_size == size) {
             end_block = init_page_buffers(page, bdev,
                         (sector_t)index << sizebits,
                         size);
             goto done;
         }
         if (!try_to_free_buffers(page_folio(page)))
             goto failed;
     }
 
     /*
      * Allocate some buffers for this page
      */
     bh = alloc_page_buffers(page, size, true);
 
     /*
      * Link the page to the buffers and initialise them.  Take the
      * lock to be atomic wrt __find_get_block(), which does not
      * run under the page lock.
      */
     spin_lock(&inode->i_mapping->private_lock);
     link_dev_buffers(page, bh);
     end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
             size);
     spin_unlock(&inode->i_mapping->private_lock);
 done:
     ret = (block < end_block) ? 1 : -ENXIO;
 failed:
     unlock_page(page);
     put_page(page);
     return ret;
 }
 
 /*
  * Create buffers for the specified block device block's page.  If
  * that page was dirty, the buffers are set dirty also.
  */
 static int
 grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
 {
     pgoff_t index;
     int sizebits;
 
     sizebits = PAGE_SHIFT - __ffs(size);
     index = block >> sizebits;
 
     /*
      * Check for a block which wants to lie outside our maximum possible
      * pagecache index.  (this comparison is done using sector_t types).
      */
     if (unlikely(index != block >> sizebits)) {
         printk(KERN_ERR "%s: requested out-of-range block %llu for "
             "device %pg\n",
             __func__, (unsigned long long)block,
             bdev);
         return -EIO;
     }
 
     /* Create a page with the proper size buffers.. */
     return grow_dev_page(bdev, block, index, size, sizebits, gfp);
 }
 
 static struct buffer_head *
 __getblk_slow(struct block_device *bdev, sector_t block,
          unsigned size, gfp_t gfp)
 {
     /* Size must be multiple of hard sectorsize */
     if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
             (size < 512 || size > PAGE_SIZE))) {
         printk(KERN_ERR "getblk(): invalid block size %d requested\n",
                     size);
         printk(KERN_ERR "logical block size: %d\n",
                     bdev_logical_block_size(bdev));
 
         dump_stack();
         return NULL;
     }
 
     for (;;) {
         struct buffer_head *bh;
         int ret;
 
         bh = __find_get_block(bdev, block, size);
         if (bh)
             return bh;
 
         ret = grow_buffers(bdev, block, size, gfp);
         if (ret < 0)
             return NULL;
     }
 }
 
 /*
  * The relationship between dirty buffers and dirty pages:
  *
  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
  * the page is tagged dirty in the page cache.
  *
  * At all times, the dirtiness of the buffers represents the dirtiness of
  * subsections of the page.  If the page has buffers, the page dirty bit is
  * merely a hint about the true dirty state.
  *
  * When a page is set dirty in its entirety, all its buffers are marked dirty
  * (if the page has buffers).
  *
  * When a buffer is marked dirty, its page is dirtied, but the page's other
  * buffers are not.
  *
  * Also.  When blockdev buffers are explicitly read with bread(), they
  * individually become uptodate.  But their backing page remains not
  * uptodate - even if all of its buffers are uptodate.  A subsequent
  * block_read_full_folio() against that folio will discover all the uptodate
  * buffers, will set the folio uptodate and will perform no I/O.
  */
 
 /**
  * mark_buffer_dirty - mark a buffer_head as needing writeout
  * @bh: the buffer_head to mark dirty
  *
  * mark_buffer_dirty() will set the dirty bit against the buffer, then set
  * its backing page dirty, then tag the page as dirty in the page cache
  * and then attach the address_space's inode to its superblock's dirty
  * inode list.
  *
  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
  * i_pages lock and mapping->host->i_lock.
  */
 void mark_buffer_dirty(struct buffer_head *bh)
 {
     WARN_ON_ONCE(!buffer_uptodate(bh));
 
     trace_block_dirty_buffer(bh);
 
     /*
      * Very *carefully* optimize the it-is-already-dirty case.
      *
      * Don't let the final "is it dirty" escape to before we
      * perhaps modified the buffer.
      */
     if (buffer_dirty(bh)) {
         smp_mb();
         if (buffer_dirty(bh))
             return;
     }
 
     if (!test_set_buffer_dirty(bh)) {
         struct page *page = bh->b_page;
         struct address_space *mapping = NULL;
 
         lock_page_memcg(page);
         if (!TestSetPageDirty(page)) {
             mapping = page_mapping(page);
             if (mapping)
                 __set_page_dirty(page, mapping, 0);
         }
         unlock_page_memcg(page);
         if (mapping)
             __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
     }
 }
 EXPORT_SYMBOL(mark_buffer_dirty);
 
 void mark_buffer_write_io_error(struct buffer_head *bh)
 {
     struct super_block *sb;
 
     set_buffer_write_io_error(bh);
     /* FIXME: do we need to set this in both places? */
     if (bh->b_page && bh->b_page->mapping)
         mapping_set_error(bh->b_page->mapping, -EIO);
     if (bh->b_assoc_map)
         mapping_set_error(bh->b_assoc_map, -EIO);
     rcu_read_lock();
     sb = READ_ONCE(bh->b_bdev->bd_super);
     if (sb)
         errseq_set(&sb->s_wb_err, -EIO);
     rcu_read_unlock();
 }
 EXPORT_SYMBOL(mark_buffer_write_io_error);
 
 /*
  * Decrement a buffer_head's reference count.  If all buffers against a page
  * have zero reference count, are clean and unlocked, and if the page is clean
  * and unlocked then try_to_free_buffers() may strip the buffers from the page
  * in preparation for freeing it (sometimes, rarely, buffers are removed from
  * a page but it ends up not being freed, and buffers may later be reattached).
  */
 void __brelse(struct buffer_head * buf)
 {
     if (atomic_read(&buf->b_count)) {
         put_bh(buf);
         return;
     }
     WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
 }
 EXPORT_SYMBOL(__brelse);
 
 /*
  * bforget() is like brelse(), except it discards any
  * potentially dirty data.
  */
 void __bforget(struct buffer_head *bh)
 {
     clear_buffer_dirty(bh);
     if (bh->b_assoc_map) {
         struct address_space *buffer_mapping = bh->b_page->mapping;
 
         spin_lock(&buffer_mapping->private_lock);
         list_del_init(&bh->b_assoc_buffers);
         bh->b_assoc_map = NULL;
         spin_unlock(&buffer_mapping->private_lock);
     }
     __brelse(bh);
 }
 EXPORT_SYMBOL(__bforget);
 
 static struct buffer_head *__bread_slow(struct buffer_head *bh)
 {
     lock_buffer(bh);
     if (buffer_uptodate(bh)) {
         unlock_buffer(bh);
         return bh;
     } else {
         get_bh(bh);
         bh->b_end_io = end_buffer_read_sync;
         submit_bh(REQ_OP_READ, bh);
         wait_on_buffer(bh);
         if (buffer_uptodate(bh))
             return bh;
     }
     brelse(bh);
     return NULL;
 }
 
 /*
  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
  * refcount elevated by one when they're in an LRU.  A buffer can only appear
  * once in a particular CPU's LRU.  A single buffer can be present in multiple
  * CPU's LRUs at the same time.
  *
  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
  * sb_find_get_block().
  *
  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
  * a local interrupt disable for that.
  */
 
 #define BH_LRU_SIZE 16
 
 struct bh_lru {
     struct buffer_head *bhs[BH_LRU_SIZE];
 };
 
 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
 
 #ifdef CONFIG_SMP
 #define bh_lru_lock()   local_irq_disable()
 #define bh_lru_unlock() local_irq_enable()
 #else
 #define bh_lru_lock()   preempt_disable()
 #define bh_lru_unlock() preempt_enable()
 #endif
 
 static inline void check_irqs_on(void)
 {
 #ifdef irqs_disabled
     BUG_ON(irqs_disabled());
 #endif
 }
 
 /*
  * Install a buffer_head into this cpu's LRU.  If not already in the LRU, it is
  * inserted at the front, and the buffer_head at the back if any is evicted.
  * Or, if already in the LRU it is moved to the front.
  */
 static void bh_lru_install(struct buffer_head *bh)
 {
     struct buffer_head *evictee = bh;
     struct bh_lru *b;
     int i;
 
     check_irqs_on();
     bh_lru_lock();
 
     /*
      * the refcount of buffer_head in bh_lru prevents dropping the
      * attached page(i.e., try_to_free_buffers) so it could cause
      * failing page migration.
      * Skip putting upcoming bh into bh_lru until migration is done.
      */
     if (lru_cache_disabled()) {
         bh_lru_unlock();
         return;
     }
 
     b = this_cpu_ptr(&bh_lrus);
     for (i = 0; i < BH_LRU_SIZE; i++) {
         swap(evictee, b->bhs[i]);
         if (evictee == bh) {
             bh_lru_unlock();
             return;
         }
     }
 
     get_bh(bh);
     bh_lru_unlock();
     brelse(evictee);
 }
 
 /*
  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
  */
 static struct buffer_head *
 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
 {
     struct buffer_head *ret = NULL;
     unsigned int i;
 
     check_irqs_on();
     bh_lru_lock();
     for (i = 0; i < BH_LRU_SIZE; i++) {
         struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
 
         if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
             bh->b_size == size) {
             if (i) {
                 while (i) {
                     __this_cpu_write(bh_lrus.bhs[i],
                         __this_cpu_read(bh_lrus.bhs[i - 1]));
                     i--;
                 }
                 __this_cpu_write(bh_lrus.bhs[0], bh);
             }
             get_bh(bh);
             ret = bh;
             break;
         }
     }
     bh_lru_unlock();
     return ret;
 }
 
 /*
  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
  * it in the LRU and mark it as accessed.  If it is not present then return
  * NULL
  */
 struct buffer_head *
 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
 {
     struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
 
     if (bh == NULL) {
         /* __find_get_block_slow will mark the page accessed */
         bh = __find_get_block_slow(bdev, block);
         if (bh)
             bh_lru_install(bh);
     } else
         touch_buffer(bh);
 
     return bh;
 }
 EXPORT_SYMBOL(__find_get_block);
 
 /*
  * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
  * which corresponds to the passed block_device, block and size. The
  * returned buffer has its reference count incremented.
  *
  * __getblk_gfp() will lock up the machine if grow_dev_page's
  * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
  */
 struct buffer_head *
 __getblk_gfp(struct block_device *bdev, sector_t block,
          unsigned size, gfp_t gfp)
 {
     struct buffer_head *bh = __find_get_block(bdev, block, size);
 
     might_sleep();
     if (bh == NULL)
         bh = __getblk_slow(bdev, block, size, gfp);
     return bh;
 }
 EXPORT_SYMBOL(__getblk_gfp);
 
 /*
  * Do async read-ahead on a buffer..
  */
 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
 {
     struct buffer_head *bh = __getblk(bdev, block, size);
     if (likely(bh)) {
         ll_rw_block(REQ_OP_READ | REQ_RAHEAD, 1, &bh);
         brelse(bh);
     }
 }
 EXPORT_SYMBOL(__breadahead);
 
 void __breadahead_gfp(struct block_device *bdev, sector_t block, unsigned size,
               gfp_t gfp)
 {
     struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
     if (likely(bh)) {
         ll_rw_block(REQ_OP_READ | REQ_RAHEAD, 1, &bh);
         brelse(bh);
     }
 }
 EXPORT_SYMBOL(__breadahead_gfp);
 
 /**
  *  __bread_gfp() - reads a specified block and returns the bh
  *  @bdev: the block_device to read from
  *  @block: number of block
  *  @size: size (in bytes) to read
  *  @gfp: page allocation flag
  *
  *  Reads a specified block, and returns buffer head that contains it.
  *  The page cache can be allocated from non-movable area
  *  not to prevent page migration if you set gfp to zero.
  *  It returns NULL if the block was unreadable.
  */
 struct buffer_head *
 __bread_gfp(struct block_device *bdev, sector_t block,
            unsigned size, gfp_t gfp)
 {
     struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
 
     if (likely(bh) && !buffer_uptodate(bh))
         bh = __bread_slow(bh);
     return bh;
 }
 EXPORT_SYMBOL(__bread_gfp);
 
 static void __invalidate_bh_lrus(struct bh_lru *b)
 {
     int i;
 
     for (i = 0; i < BH_LRU_SIZE; i++) {
         brelse(b->bhs[i]);
         b->bhs[i] = NULL;
     }
 }
 /*
  * invalidate_bh_lrus() is called rarely - but not only at unmount.
  * This doesn't race because it runs in each cpu either in irq
  * or with preempt disabled.
  */
 static void invalidate_bh_lru(void *arg)
 {
     struct bh_lru *b = &get_cpu_var(bh_lrus);
 
     __invalidate_bh_lrus(b);
     put_cpu_var(bh_lrus);
 }
 
 bool has_bh_in_lru(int cpu, void *dummy)
 {
     struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
     int i;
     
     for (i = 0; i < BH_LRU_SIZE; i++) {
         if (b->bhs[i])
             return true;
     }
 
     return false;
 }
 
 void invalidate_bh_lrus(void)
 {
     on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1);
 }
 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
 
 /*
  * It's called from workqueue context so we need a bh_lru_lock to close
  * the race with preemption/irq.
  */
 void invalidate_bh_lrus_cpu(void)
 {
     struct bh_lru *b;
 
     bh_lru_lock();
     b = this_cpu_ptr(&bh_lrus);
     __invalidate_bh_lrus(b);
     bh_lru_unlock();
 }
 
 void set_bh_page(struct buffer_head *bh,
         struct page *page, unsigned long offset)
 {
     bh->b_page = page;
     BUG_ON(offset >= PAGE_SIZE);
     if (PageHighMem(page))
         /*
          * This catches illegal uses and preserves the offset:
          */
         bh->b_data = (char *)(0 + offset);
     else
         bh->b_data = page_address(page) + offset;
 }
 EXPORT_SYMBOL(set_bh_page);
 
 /*
  * Called when truncating a buffer on a page completely.
  */
 
 /* Bits that are cleared during an invalidate */
 #define BUFFER_FLAGS_DISCARD \
     (1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
      1 << BH_Delay | 1 << BH_Unwritten)
 
 static void discard_buffer(struct buffer_head * bh)
 {
     unsigned long b_state, b_state_old;
 
     lock_buffer(bh);
     clear_buffer_dirty(bh);
     bh->b_bdev = NULL;
     b_state = bh->b_state;
     for (;;) {
         b_state_old = cmpxchg(&bh->b_state, b_state,
                       (b_state & ~BUFFER_FLAGS_DISCARD));
         if (b_state_old == b_state)
             break;
         b_state = b_state_old;
     }
     unlock_buffer(bh);
 }
 
 /**
  * block_invalidate_folio - Invalidate part or all of a buffer-backed folio.
  * @folio: The folio which is affected.
  * @offset: start of the range to invalidate
  * @length: length of the range to invalidate
  *
  * block_invalidate_folio() is called when all or part of the folio has been
  * invalidated by a truncate operation.
  *
  * block_invalidate_folio() does not have to release all buffers, but it must
  * ensure that no dirty buffer is left outside @offset and that no I/O
  * is underway against any of the blocks which are outside the truncation
  * point.  Because the caller is about to free (and possibly reuse) those
  * blocks on-disk.
  */
 void block_invalidate_folio(struct folio *folio, size_t offset, size_t length)
 {
     struct buffer_head *head, *bh, *next;
     size_t curr_off = 0;
     size_t stop = length + offset;
 
     BUG_ON(!folio_test_locked(folio));
 
     /*
      * Check for overflow
      */
     BUG_ON(stop > folio_size(folio) || stop < length);
 
     head = folio_buffers(folio);
     if (!head)
         return;
 
     bh = head;
     do {
         size_t next_off = curr_off + bh->b_size;
         next = bh->b_this_page;
 
         /*
          * Are we still fully in range ?
          */
         if (next_off > stop)
             goto out;
 
         /*
          * is this block fully invalidated?
          */
         if (offset <= curr_off)
             discard_buffer(bh);
         curr_off = next_off;
         bh = next;
     } while (bh != head);
 
     /*
      * We release buffers only if the entire folio is being invalidated.
      * The get_block cached value has been unconditionally invalidated,
      * so real IO is not possible anymore.
      */
     if (length == folio_size(folio))
         filemap_release_folio(folio, 0);
 out:
     return;
 }
 EXPORT_SYMBOL(block_invalidate_folio);
 
 
 /*
  * We attach and possibly dirty the buffers atomically wrt
  * block_dirty_folio() via private_lock.  try_to_free_buffers
  * is already excluded via the page lock.
  */
 void create_empty_buffers(struct page *page,
             unsigned long blocksize, unsigned long b_state)
 {
     struct buffer_head *bh, *head, *tail;
 
     head = alloc_page_buffers(page, blocksize, true);
     bh = head;
     do {
         bh->b_state |= b_state;
         tail = bh;
         bh = bh->b_this_page;
     } while (bh);
     tail->b_this_page = head;
 
     spin_lock(&page->mapping->private_lock);
     if (PageUptodate(page) || PageDirty(page)) {
         bh = head;
         do {
             if (PageDirty(page))
                 set_buffer_dirty(bh);
             if (PageUptodate(page))
                 set_buffer_uptodate(bh);
             bh = bh->b_this_page;
         } while (bh != head);
     }
     attach_page_private(page, head);
     spin_unlock(&page->mapping->private_lock);
 }
 EXPORT_SYMBOL(create_empty_buffers);
 
 /**
  * clean_bdev_aliases: clean a range of buffers in block device
  * @bdev: Block device to clean buffers in
  * @block: Start of a range of blocks to clean
  * @len: Number of blocks to clean
  *
  * We are taking a range of blocks for data and we don't want writeback of any
  * buffer-cache aliases starting from return from this function and until the
  * moment when something will explicitly mark the buffer dirty (hopefully that
  * will not happen until we will free that block ;-) We don't even need to mark
  * it not-uptodate - nobody can expect anything from a newly allocated buffer
  * anyway. We used to use unmap_buffer() for such invalidation, but that was
  * wrong. We definitely don't want to mark the alias unmapped, for example - it
  * would confuse anyone who might pick it with bread() afterwards...
  *
  * Also..  Note that bforget() doesn't lock the buffer.  So there can be
  * writeout I/O going on against recently-freed buffers.  We don't wait on that
  * I/O in bforget() - it's more efficient to wait on the I/O only if we really
  * need to.  That happens here.
  */
 void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
 {
     struct inode *bd_inode = bdev->bd_inode;
     struct address_space *bd_mapping = bd_inode->i_mapping;
     struct folio_batch fbatch;
     pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
     pgoff_t end;
     int i, count;
     struct buffer_head *bh;
     struct buffer_head *head;
 
     end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
     folio_batch_init(&fbatch);
     while (filemap_get_folios(bd_mapping, &index, end, &fbatch)) {
         count = folio_batch_count(&fbatch);
         for (i = 0; i < count; i++) {
             struct folio *folio = fbatch.folios[i];
 
             if (!folio_buffers(folio))
                 continue;
             /*
              * We use folio lock instead of bd_mapping->private_lock
              * to pin buffers here since we can afford to sleep and
              * it scales better than a global spinlock lock.
              */
             folio_lock(folio);
             /* Recheck when the folio is locked which pins bhs */
             head = folio_buffers(folio);
             if (!head)
                 goto unlock_page;
             bh = head;
             do {
                 if (!buffer_mapped(bh) || (bh->b_blocknr < block))
                     goto next;
                 if (bh->b_blocknr >= block + len)
                     break;
                 clear_buffer_dirty(bh);
                 wait_on_buffer(bh);
                 clear_buffer_req(bh);
 next:
                 bh = bh->b_this_page;
             } while (bh != head);
 unlock_page:
             folio_unlock(folio);
         }
         folio_batch_release(&fbatch);
         cond_resched();
         /* End of range already reached? */
         if (index > end || !index)
             break;
     }
 }
 EXPORT_SYMBOL(clean_bdev_aliases);
 
 /*
  * Size is a power-of-two in the range 512..PAGE_SIZE,
  * and the case we care about most is PAGE_SIZE.
  *
  * So this *could* possibly be written with those
  * constraints in mind (relevant mostly if some
  * architecture has a slow bit-scan instruction)
  */
 static inline int block_size_bits(unsigned int blocksize)
 {
     return ilog2(blocksize);
 }
 
 static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
 {
     BUG_ON(!PageLocked(page));
 
     if (!page_has_buffers(page))
         create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
                      b_state);
     return page_buffers(page);
 }
 
 /*
  * NOTE! All mapped/uptodate combinations are valid:
  *
  *  Mapped  Uptodate    Meaning
  *
  *  No  No      "unknown" - must do get_block()
  *  No  Yes     "hole" - zero-filled
  *  Yes No      "allocated" - allocated on disk, not read in
  *  Yes Yes     "valid" - allocated and up-to-date in memory.
  *
  * "Dirty" is valid only with the last case (mapped+uptodate).
  */
 
 /*
  * While block_write_full_page is writing back the dirty buffers under
  * the page lock, whoever dirtied the buffers may decide to clean them
  * again at any time.  We handle that by only looking at the buffer
  * state inside lock_buffer().
  *
  * If block_write_full_page() is called for regular writeback
  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
  * locked buffer.   This only can happen if someone has written the buffer
  * directly, with submit_bh().  At the address_space level PageWriteback
  * prevents this contention from occurring.
  *
  * If block_write_full_page() is called with wbc->sync_mode ==
  * WB_SYNC_ALL, the writes are posted using REQ_SYNC; this
  * causes the writes to be flagged as synchronous writes.
  */
 int __block_write_full_page(struct inode *inode, struct page *page,
             get_block_t *get_block, struct writeback_control *wbc,
             bh_end_io_t *handler)
 {
     int err;
     sector_t block;
     sector_t last_block;
     struct buffer_head *bh, *head;
     unsigned int blocksize, bbits;
     int nr_underway = 0;
     blk_opf_t write_flags = wbc_to_write_flags(wbc);
 
     head = create_page_buffers(page, inode,
                     (1 << BH_Dirty)|(1 << BH_Uptodate));
 
     /*
      * Be very careful.  We have no exclusion from block_dirty_folio
      * here, and the (potentially unmapped) buffers may become dirty at
      * any time.  If a buffer becomes dirty here after we've inspected it
      * then we just miss that fact, and the page stays dirty.
      *
      * Buffers outside i_size may be dirtied by block_dirty_folio;
      * handle that here by just cleaning them.
      */
 
     bh = head;
     blocksize = bh->b_size;
     bbits = block_size_bits(blocksize);
 
     block = (sector_t)page->index << (PAGE_SHIFT - bbits);
     last_block = (i_size_read(inode) - 1) >> bbits;
 
     /*
      * Get all the dirty buffers mapped to disk addresses and
      * handle any aliases from the underlying blockdev's mapping.
      */
     do {
         if (block > last_block) {
             /*
              * mapped buffers outside i_size will occur, because
              * this page can be outside i_size when there is a
              * truncate in progress.
              */
             /*
              * The buffer was zeroed by block_write_full_page()
              */
             clear_buffer_dirty(bh);
             set_buffer_uptodate(bh);
         } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
                buffer_dirty(bh)) {
             WARN_ON(bh->b_size != blocksize);
             err = get_block(inode, block, bh, 1);
             if (err)
                 goto recover;
             clear_buffer_delay(bh);
             if (buffer_new(bh)) {
                 /* blockdev mappings never come here */
                 clear_buffer_new(bh);
                 clean_bdev_bh_alias(bh);
             }
         }
         bh = bh->b_this_page;
         block++;
     } while (bh != head);
 
     do {
         if (!buffer_mapped(bh))
             continue;
         /*
          * If it's a fully non-blocking write attempt and we cannot
          * lock the buffer then redirty the page.  Note that this can
          * potentially cause a busy-wait loop from writeback threads
          * and kswapd activity, but those code paths have their own
          * higher-level throttling.
          */
         if (wbc->sync_mode != WB_SYNC_NONE) {
             lock_buffer(bh);
         } else if (!trylock_buffer(bh)) {
             redirty_page_for_writepage(wbc, page);
             continue;
         }
         if (test_clear_buffer_dirty(bh)) {
             mark_buffer_async_write_endio(bh, handler);
         } else {
             unlock_buffer(bh);
         }
     } while ((bh = bh->b_this_page) != head);
 
     /*
      * The page and its buffers are protected by PageWriteback(), so we can
      * drop the bh refcounts early.
      */
     BUG_ON(PageWriteback(page));
     set_page_writeback(page);
 
     do {
         struct buffer_head *next = bh->b_this_page;
         if (buffer_async_write(bh)) {
             submit_bh_wbc(REQ_OP_WRITE | write_flags, bh, wbc);
             nr_underway++;
         }
         bh = next;
     } while (bh != head);
     unlock_page(page);
 
     err = 0;
 done:
     if (nr_underway == 0) {
         /*
          * The page was marked dirty, but the buffers were
          * clean.  Someone wrote them back by hand with
          * ll_rw_block/submit_bh.  A rare case.
          */
         end_page_writeback(page);
 
         /*
          * The page and buffer_heads can be released at any time from
          * here on.
          */
     }
     return err;
 
 recover:
     /*
      * ENOSPC, or some other error.  We may already have added some
      * blocks to the file, so we need to write these out to avoid
      * exposing stale data.
      * The page is currently locked and not marked for writeback
      */
     bh = head;
     /* Recovery: lock and submit the mapped buffers */
     do {
         if (buffer_mapped(bh) && buffer_dirty(bh) &&
             !buffer_delay(bh)) {
             lock_buffer(bh);
             mark_buffer_async_write_endio(bh, handler);
         } else {
             /*
              * The buffer may have been set dirty during
              * attachment to a dirty page.
              */
             clear_buffer_dirty(bh);
         }
     } while ((bh = bh->b_this_page) != head);
     SetPageError(page);
     BUG_ON(PageWriteback(page));
     mapping_set_error(page->mapping, err);
     set_page_writeback(page);
     do {
         struct buffer_head *next = bh->b_this_page;
         if (buffer_async_write(bh)) {
             clear_buffer_dirty(bh);
             submit_bh_wbc(REQ_OP_WRITE | write_flags, bh, wbc);
             nr_underway++;
         }
         bh = next;
     } while (bh != head);
     unlock_page(page);
     goto done;
 }
 EXPORT_SYMBOL(__block_write_full_page);
 
 /*
  * If a page has any new buffers, zero them out here, and mark them uptodate
  * and dirty so they'll be written out (in order to prevent uninitialised
  * block data from leaking). And clear the new bit.
  */
 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
 {
     unsigned int block_start, block_end;
     struct buffer_head *head, *bh;
 
     BUG_ON(!PageLocked(page));
     if (!page_has_buffers(page))
         return;
 
     bh = head = page_buffers(page);
     block_start = 0;
     do {
         block_end = block_start + bh->b_size;
 
         if (buffer_new(bh)) {
             if (block_end > from && block_start < to) {
                 if (!PageUptodate(page)) {
                     unsigned start, size;
 
                     start = max(from, block_start);
                     size = min(to, block_end) - start;
 
                     zero_user(page, start, size);
                     set_buffer_uptodate(bh);
                 }
 
                 clear_buffer_new(bh);
                 mark_buffer_dirty(bh);
             }
         }
 
         block_start = block_end;
         bh = bh->b_this_page;
     } while (bh != head);
 }
 EXPORT_SYMBOL(page_zero_new_buffers);
 
 static void
 iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
         const struct iomap *iomap)
 {
     loff_t offset = block << inode->i_blkbits;
 
     bh->b_bdev = iomap->bdev;
 
     /*
      * Block points to offset in file we need to map, iomap contains
      * the offset at which the map starts. If the map ends before the
      * current block, then do not map the buffer and let the caller
      * handle it.
      */
     BUG_ON(offset >= iomap->offset + iomap->length);
 
     switch (iomap->type) {
     case IOMAP_HOLE:
         /*
          * If the buffer is not up to date or beyond the current EOF,
          * we need to mark it as new to ensure sub-block zeroing is
          * executed if necessary.
          */
         if (!buffer_uptodate(bh) ||
             (offset >= i_size_read(inode)))
             set_buffer_new(bh);
         break;
     case IOMAP_DELALLOC:
         if (!buffer_uptodate(bh) ||
             (offset >= i_size_read(inode)))
             set_buffer_new(bh);
         set_buffer_uptodate(bh);
         set_buffer_mapped(bh);
         set_buffer_delay(bh);
         break;
     case IOMAP_UNWRITTEN:
         /*
          * For unwritten regions, we always need to ensure that regions
          * in the block we are not writing to are zeroed. Mark the
          * buffer as new to ensure this.
          */
         set_buffer_new(bh);
         set_buffer_unwritten(bh);
         fallthrough;
     case IOMAP_MAPPED:
         if ((iomap->flags & IOMAP_F_NEW) ||
             offset >= i_size_read(inode))
             set_buffer_new(bh);
         bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
                 inode->i_blkbits;
         set_buffer_mapped(bh);
         break;
     }
 }
 
 int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
         get_block_t *get_block, const struct iomap *iomap)
 {
     unsigned from = pos & (PAGE_SIZE - 1);
     unsigned to = from + len;
     struct inode *inode = folio->mapping->host;
     unsigned block_start, block_end;
     sector_t block;
     int err = 0;
     unsigned blocksize, bbits;
     struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
 
     BUG_ON(!folio_test_locked(folio));
     BUG_ON(from > PAGE_SIZE);
     BUG_ON(to > PAGE_SIZE);
     BUG_ON(from > to);
 
     head = create_page_buffers(&folio->page, inode, 0);
     blocksize = head->b_size;
     bbits = block_size_bits(blocksize);
 
     block = (sector_t)folio->index << (PAGE_SHIFT - bbits);
 
     for(bh = head, block_start = 0; bh != head || !block_start;
         block++, block_start=block_end, bh = bh->b_this_page) {
         block_end = block_start + blocksize;
         if (block_end <= from || block_start >= to) {
             if (folio_test_uptodate(folio)) {
                 if (!buffer_uptodate(bh))
                     set_buffer_uptodate(bh);
             }
             continue;
         }
         if (buffer_new(bh))
             clear_buffer_new(bh);
         if (!buffer_mapped(bh)) {
             WARN_ON(bh->b_size != blocksize);
             if (get_block) {
                 err = get_block(inode, block, bh, 1);
                 if (err)
                     break;
             } else {
                 iomap_to_bh(inode, block, bh, iomap);
             }
 
             if (buffer_new(bh)) {
                 clean_bdev_bh_alias(bh);
                 if (folio_test_uptodate(folio)) {
                     clear_buffer_new(bh);
                     set_buffer_uptodate(bh);
                     mark_buffer_dirty(bh);
                     continue;
                 }
                 if (block_end > to || block_start < from)
                     folio_zero_segments(folio,
                         to, block_end,
                         block_start, from);
                 continue;
             }
         }
         if (folio_test_uptodate(folio)) {
             if (!buffer_uptodate(bh))
                 set_buffer_uptodate(bh);
             continue; 
         }
         if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
             !buffer_unwritten(bh) &&
              (block_start < from || block_end > to)) {
             ll_rw_block(REQ_OP_READ, 1, &bh);
             *wait_bh++=bh;
         }
     }
     /*
      * If we issued read requests - let them complete.
      */
     while(wait_bh > wait) {
         wait_on_buffer(*--wait_bh);
         if (!buffer_uptodate(*wait_bh))
             err = -EIO;
     }
     if (unlikely(err))
         page_zero_new_buffers(&folio->page, from, to);
     return err;
 }
 
 int __block_write_begin(struct page *page, loff_t pos, unsigned len,
         get_block_t *get_block)
 {
     return __block_write_begin_int(page_folio(page), pos, len, get_block,
                        NULL);
 }
 EXPORT_SYMBOL(__block_write_begin);
 
 static int __block_commit_write(struct inode *inode, struct page *page,
         unsigned from, unsigned to)
 {
     unsigned block_start, block_end;
     int partial = 0;
     unsigned blocksize;
     struct buffer_head *bh, *head;
 
     bh = head = page_buffers(page);
     blocksize = bh->b_size;
 
     block_start = 0;
     do {
         block_end = block_start + blocksize;
         if (block_end <= from || block_start >= to) {
             if (!buffer_uptodate(bh))
                 partial = 1;
         } else {
             set_buffer_uptodate(bh);
             mark_buffer_dirty(bh);
         }
         if (buffer_new(bh))
             clear_buffer_new(bh);
 
         block_start = block_end;
         bh = bh->b_this_page;
     } while (bh != head);
 
     /*
      * If this is a partial write which happened to make all buffers
      * uptodate then we can optimize away a bogus read_folio() for
      * the next read(). Here we 'discover' whether the page went
      * uptodate as a result of this (potentially partial) write.
      */
     if (!partial)
         SetPageUptodate(page);
     return 0;
 }
 
 /*
  * block_write_begin takes care of the basic task of block allocation and
  * bringing partial write blocks uptodate first.
  *
  * The filesystem needs to handle block truncation upon failure.
  */
 int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
         struct page **pagep, get_block_t *get_block)
 {
     pgoff_t index = pos >> PAGE_SHIFT;
     struct page *page;
     int status;
 
     page = grab_cache_page_write_begin(mapping, index);
     if (!page)
         return -ENOMEM;
 
     status = __block_write_begin(page, pos, len, get_block);
     if (unlikely(status)) {
         unlock_page(page);
         put_page(page);
         page = NULL;
     }
 
     *pagep = page;
     return status;
 }
 EXPORT_SYMBOL(block_write_begin);
 
 int block_write_end(struct file *file, struct address_space *mapping,
             loff_t pos, unsigned len, unsigned copied,
             struct page *page, void *fsdata)
 {
     struct inode *inode = mapping->host;
     unsigned start;
 
     start = pos & (PAGE_SIZE - 1);
 
     if (unlikely(copied < len)) {
         /*
          * The buffers that were written will now be uptodate, so
          * we don't have to worry about a read_folio reading them
          * and overwriting a partial write. However if we have
          * encountered a short write and only partially written
          * into a buffer, it will not be marked uptodate, so a
          * read_folio might come in and destroy our partial write.
          *
          * Do the simplest thing, and just treat any short write to a
          * non uptodate page as a zero-length write, and force the
          * caller to redo the whole thing.
          */
         if (!PageUptodate(page))
             copied = 0;
 
         page_zero_new_buffers(page, start+copied, start+len);
     }
     flush_dcache_page(page);
 
     /* This could be a short (even 0-length) commit */
     __block_commit_write(inode, page, start, start+copied);
 
     return copied;
 }
 EXPORT_SYMBOL(block_write_end);
 
 int generic_write_end(struct file *file, struct address_space *mapping,
             loff_t pos, unsigned len, unsigned copied,
             struct page *page, void *fsdata)
 {
     struct inode *inode = mapping->host;
     loff_t old_size = inode->i_size;
     bool i_size_changed = false;
 
     copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
 
     /*
      * No need to use i_size_read() here, the i_size cannot change under us
      * because we hold i_rwsem.
      *
      * But it's important to update i_size while still holding page lock:
      * page writeout could otherwise come in and zero beyond i_size.
      */
     if (pos + copied > inode->i_size) {
         i_size_write(inode, pos + copied);
         i_size_changed = true;
     }
 
     unlock_page(page);
     put_page(page);
 
     if (old_size < pos)
         pagecache_isize_extended(inode, old_size, pos);
     /*
      * Don't mark the inode dirty under page lock. First, it unnecessarily
      * makes the holding time of page lock longer. Second, it forces lock
      * ordering of page lock and transaction start for journaling
      * filesystems.
      */
     if (i_size_changed)
         mark_inode_dirty(inode);
     return copied;
 }
 EXPORT_SYMBOL(generic_write_end);
 
 /*
  * block_is_partially_uptodate checks whether buffers within a folio are
  * uptodate or not.
  *
  * Returns true if all buffers which correspond to the specified part
  * of the folio are uptodate.
  */
 bool block_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
 {
     unsigned block_start, block_end, blocksize;
     unsigned to;
     struct buffer_head *bh, *head;
     bool ret = true;
 
     head = folio_buffers(folio);
     if (!head)
         return false;
     blocksize = head->b_size;
     to = min_t(unsigned, folio_size(folio) - from, count);
     to = from + to;
     if (from < blocksize && to > folio_size(folio) - blocksize)
         return false;
 
     bh = head;
     block_start = 0;
     do {
         block_end = block_start + blocksize;
         if (block_end > from && block_start < to) {
             if (!buffer_uptodate(bh)) {
                 ret = false;
                 break;
             }
             if (block_end >= to)
                 break;
         }
         block_start = block_end;
         bh = bh->b_this_page;
     } while (bh != head);
 
     return ret;
 }
 EXPORT_SYMBOL(block_is_partially_uptodate);
 
 /*
  * Generic "read_folio" function for block devices that have the normal
  * get_block functionality. This is most of the block device filesystems.
  * Reads the folio asynchronously --- the unlock_buffer() and
  * set/clear_buffer_uptodate() functions propagate buffer state into the
  * folio once IO has completed.
  */
 int block_read_full_folio(struct folio *folio, get_block_t *get_block)
 {
     struct inode *inode = folio->mapping->host;
     sector_t iblock, lblock;
     struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
     unsigned int blocksize, bbits;
     int nr, i;
     int fully_mapped = 1;
     bool page_error = false;
 
     VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
 
     head = create_page_buffers(&folio->page, inode, 0);
     blocksize = head->b_size;
     bbits = block_size_bits(blocksize);
 
     iblock = (sector_t)folio->index << (PAGE_SHIFT - bbits);
     lblock = (i_size_read(inode)+blocksize-1) >> bbits;
     bh = head;
     nr = 0;
     i = 0;
 
     do {
         if (buffer_uptodate(bh))
             continue;
 
         if (!buffer_mapped(bh)) {
             int err = 0;
 
             fully_mapped = 0;
             if (iblock < lblock) {
                 WARN_ON(bh->b_size != blocksize);
                 err = get_block(inode, iblock, bh, 0);
                 if (err) {
                     folio_set_error(folio);
                     page_error = true;
                 }
             }
             if (!buffer_mapped(bh)) {
                 folio_zero_range(folio, i * blocksize,
                         blocksize);
                 if (!err)
                     set_buffer_uptodate(bh);
                 continue;
             }
             /*
              * get_block() might have updated the buffer
              * synchronously
              */
             if (buffer_uptodate(bh))
                 continue;
         }
         arr[nr++] = bh;
     } while (i++, iblock++, (bh = bh->b_this_page) != head);
 
     if (fully_mapped)
         folio_set_mappedtodisk(folio);
 
     if (!nr) {
         /*
          * All buffers are uptodate - we can set the folio uptodate
          * as well. But not if get_block() returned an error.
          */
         if (!page_error)
             folio_mark_uptodate(folio);
         folio_unlock(folio);
         return 0;
     }
 
     /* Stage two: lock the buffers */
     for (i = 0; i < nr; i++) {
         bh = arr[i];
         lock_buffer(bh);
         mark_buffer_async_read(bh);
     }
 
     /*
      * Stage 3: start the IO.  Check for uptodateness
      * inside the buffer lock in case another process reading
      * the underlying blockdev brought it uptodate (the sct fix).
      */
     for (i = 0; i < nr; i++) {
         bh = arr[i];
         if (buffer_uptodate(bh))
             end_buffer_async_read(bh, 1);
         else
             submit_bh(REQ_OP_READ, bh);
     }
     return 0;
 }
 EXPORT_SYMBOL(block_read_full_folio);
 
 /* utility function for filesystems that need to do work on expanding
  * truncates.  Uses filesystem pagecache writes to allow the filesystem to
  * deal with the hole.  
  */
 int generic_cont_expand_simple(struct inode *inode, loff_t size)
 {
     struct address_space *mapping = inode->i_mapping;
     const struct address_space_operations *aops = mapping->a_ops;
     struct page *page;
     void *fsdata;
     int err;
 
     err = inode_newsize_ok(inode, size);
     if (err)
         goto out;
 
     err = aops->write_begin(NULL, mapping, size, 0, &page, &fsdata);
     if (err)
         goto out;
 
     err = aops->write_end(NULL, mapping, size, 0, 0, page, fsdata);
     BUG_ON(err > 0);
 
 out:
     return err;
 }
 EXPORT_SYMBOL(generic_cont_expand_simple);
 
 static int cont_expand_zero(struct file *file, struct address_space *mapping,
                 loff_t pos, loff_t *bytes)
 {
     struct inode *inode = mapping->host;
     const struct address_space_operations *aops = mapping->a_ops;
     unsigned int blocksize = i_blocksize(inode);
     struct page *page;
     void *fsdata;
     pgoff_t index, curidx;
     loff_t curpos;
     unsigned zerofrom, offset, len;
     int err = 0;
 
     index = pos >> PAGE_SHIFT;
     offset = pos & ~PAGE_MASK;
 
     while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
         zerofrom = curpos & ~PAGE_MASK;
         if (zerofrom & (blocksize-1)) {
             *bytes |= (blocksize-1);
             (*bytes)++;
         }
         len = PAGE_SIZE - zerofrom;
 
         err = aops->write_begin(file, mapping, curpos, len,
                         &page, &fsdata);
         if (err)
             goto out;
         zero_user(page, zerofrom, len);
         err = aops->write_end(file, mapping, curpos, len, len,
                         page, fsdata);
         if (err < 0)
             goto out;
         BUG_ON(err != len);
         err = 0;
 
         balance_dirty_pages_ratelimited(mapping);
 
         if (fatal_signal_pending(current)) {
             err = -EINTR;
             goto out;
         }
     }
 
     /* page covers the boundary, find the boundary offset */
     if (index == curidx) {
         zerofrom = curpos & ~PAGE_MASK;
         /* if we will expand the thing last block will be filled */
         if (offset <= zerofrom) {
             goto out;
         }
         if (zerofrom & (blocksize-1)) {
             *bytes |= (blocksize-1);
             (*bytes)++;
         }
         len = offset - zerofrom;
 
         err = aops->write_begin(file, mapping, curpos, len,
                         &page, &fsdata);
         if (err)
             goto out;
         zero_user(page, zerofrom, len);
         err = aops->write_end(file, mapping, curpos, len, len,
                         page, fsdata);
         if (err < 0)
             goto out;
         BUG_ON(err != len);
         err = 0;
     }
 out:
     return err;
 }
 
 /*
  * For moronic filesystems that do not allow holes in file.
  * We may have to extend the file.
  */
 int cont_write_begin(struct file *file, struct address_space *mapping,
             loff_t pos, unsigned len,
             struct page **pagep, void **fsdata,
             get_block_t *get_block, loff_t *bytes)
 {
     struct inode *inode = mapping->host;
     unsigned int blocksize = i_blocksize(inode);
     unsigned int zerofrom;
     int err;
 
     err = cont_expand_zero(file, mapping, pos, bytes);
     if (err)
         return err;
 
     zerofrom = *bytes & ~PAGE_MASK;
     if (pos+len > *bytes && zerofrom & (blocksize-1)) {
         *bytes |= (blocksize-1);
         (*bytes)++;
     }
 
     return block_write_begin(mapping, pos, len, pagep, get_block);
 }
 EXPORT_SYMBOL(cont_write_begin);
 
 int block_commit_write(struct page *page, unsigned from, unsigned to)
 {
     struct inode *inode = page->mapping->host;
     __block_commit_write(inode,page,from,to);
     return 0;
 }
 EXPORT_SYMBOL(block_commit_write);
 
 /*
  * block_page_mkwrite() is not allowed to change the file size as it gets
  * called from a page fault handler when a page is first dirtied. Hence we must
  * be careful to check for EOF conditions here. We set the page up correctly
  * for a written page which means we get ENOSPC checking when writing into
  * holes and correct delalloc and unwritten extent mapping on filesystems that
  * support these features.
  *
  * We are not allowed to take the i_mutex here so we have to play games to
  * protect against truncate races as the page could now be beyond EOF.  Because
  * truncate writes the inode size before removing pages, once we have the
  * page lock we can determine safely if the page is beyond EOF. If it is not
  * beyond EOF, then the page is guaranteed safe against truncation until we
  * unlock the page.
  *
  * Direct callers of this function should protect against filesystem freezing
  * using sb_start_pagefault() - sb_end_pagefault() functions.
  */
 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
              get_block_t get_block)
 {
     struct page *page = vmf->page;
     struct inode *inode = file_inode(vma->vm_file);
     unsigned long end;
     loff_t size;
     int ret;
 
     lock_page(page);
     size = i_size_read(inode);
     if ((page->mapping != inode->i_mapping) ||
         (page_offset(page) > size)) {
         /* We overload EFAULT to mean page got truncated */
         ret = -EFAULT;
         goto out_unlock;
     }
 
     /* page is wholly or partially inside EOF */
     if (((page->index + 1) << PAGE_SHIFT) > size)
         end = size & ~PAGE_MASK;
     else
         end = PAGE_SIZE;
 
     ret = __block_write_begin(page, 0, end, get_block);
     if (!ret)
         ret = block_commit_write(page, 0, end);
 
     if (unlikely(ret < 0))
         goto out_unlock;
     set_page_dirty(page);
     wait_for_stable_page(page);
     return 0;
 out_unlock:
     unlock_page(page);
     return ret;
 }
 EXPORT_SYMBOL(block_page_mkwrite);
 
 int block_truncate_page(struct address_space *mapping,
             loff_t from, get_block_t *get_block)
 {
     pgoff_t index = from >> PAGE_SHIFT;
     unsigned offset = from & (PAGE_SIZE-1);
     unsigned blocksize;
     sector_t iblock;
     unsigned length, pos;
     struct inode *inode = mapping->host;
     struct page *page;
     struct buffer_head *bh;
     int err;
 
     blocksize = i_blocksize(inode);
     length = offset & (blocksize - 1);
 
     /* Block boundary? Nothing to do */
     if (!length)
         return 0;
 
     length = blocksize - length;
     iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
     
     page = grab_cache_page(mapping, index);
     err = -ENOMEM;
     if (!page)
         goto out;
 
     if (!page_has_buffers(page))
         create_empty_buffers(page, blocksize, 0);
 
     /* Find the buffer that contains "offset" */
     bh = page_buffers(page);
     pos = blocksize;
     while (offset >= pos) {
         bh = bh->b_this_page;
         iblock++;
         pos += blocksize;
     }
 
     err = 0;
     if (!buffer_mapped(bh)) {
         WARN_ON(bh->b_size != blocksize);
         err = get_block(inode, iblock, bh, 0);
         if (err)
             goto unlock;
         /* unmapped? It's a hole - nothing to do */
         if (!buffer_mapped(bh))
             goto unlock;
     }
 
     /* Ok, it's mapped. Make sure it's up-to-date */
     if (PageUptodate(page))
         set_buffer_uptodate(bh);
 
     if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
         err = -EIO;
         ll_rw_block(REQ_OP_READ, 1, &bh);
         wait_on_buffer(bh);
         /* Uhhuh. Read error. Complain and punt. */
         if (!buffer_uptodate(bh))
             goto unlock;
     }
 
     zero_user(page, offset, length);
     mark_buffer_dirty(bh);
     err = 0;
 
 unlock:
     unlock_page(page);
     put_page(page);
 out:
     return err;
 }
 EXPORT_SYMBOL(block_truncate_page);
 
 /*
  * The generic ->writepage function for buffer-backed address_spaces
  */
 int block_write_full_page(struct page *page, get_block_t *get_block,
             struct writeback_control *wbc)
 {
     struct inode * const inode = page->mapping->host;
     loff_t i_size = i_size_read(inode);
     const pgoff_t end_index = i_size >> PAGE_SHIFT;
     unsigned offset;
 
     /* Is the page fully inside i_size? */
     if (page->index < end_index)
         return __block_write_full_page(inode, page, get_block, wbc,
                            end_buffer_async_write);
 
     /* Is the page fully outside i_size? (truncate in progress) */
     offset = i_size & (PAGE_SIZE-1);
     if (page->index >= end_index+1 || !offset) {
         unlock_page(page);
         return 0; /* don't care */
     }
 
     /*
      * The page straddles i_size.  It must be zeroed out on each and every
      * writepage invocation because it may be mmapped.  "A file is mapped
      * in multiples of the page size.  For a file that is not a multiple of
      * the  page size, the remaining memory is zeroed when mapped, and
      * writes to that region are not written out to the file."
      */
     zero_user_segment(page, offset, PAGE_SIZE);
     return __block_write_full_page(inode, page, get_block, wbc,
                             end_buffer_async_write);
 }
 EXPORT_SYMBOL(block_write_full_page);
 
 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
                 get_block_t *get_block)
 {
     struct inode *inode = mapping->host;
     struct buffer_head tmp = {
         .b_size = i_blocksize(inode),
     };
 
     get_block(inode, block, &tmp, 0);
     return tmp.b_blocknr;
 }
 EXPORT_SYMBOL(generic_block_bmap);
 
 static void end_bio_bh_io_sync(struct bio *bio)
 {
     struct buffer_head *bh = bio->bi_private;
 
     if (unlikely(bio_flagged(bio, BIO_QUIET)))
         set_bit(BH_Quiet, &bh->b_state);
 
     bh->b_end_io(bh, !bio->bi_status);
     bio_put(bio);
 }
 
 static int submit_bh_wbc(blk_opf_t opf, struct buffer_head *bh,
              struct writeback_control *wbc)
 {
     const enum req_op op = opf & REQ_OP_MASK;
     struct bio *bio;
 
     BUG_ON(!buffer_locked(bh));
     BUG_ON(!buffer_mapped(bh));
     BUG_ON(!bh->b_end_io);
     BUG_ON(buffer_delay(bh));
     BUG_ON(buffer_unwritten(bh));
 
     /*
      * Only clear out a write error when rewriting
      */
     if (test_set_buffer_req(bh) && (op == REQ_OP_WRITE))
         clear_buffer_write_io_error(bh);
 
     if (buffer_meta(bh))
         opf |= REQ_META;
     if (buffer_prio(bh))
         opf |= REQ_PRIO;
 
     bio = bio_alloc(bh->b_bdev, 1, opf, GFP_NOIO);
 
     fscrypt_set_bio_crypt_ctx_bh(bio, bh, GFP_NOIO);
 
     bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
 
     bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
     BUG_ON(bio->bi_iter.bi_size != bh->b_size);
 
     bio->bi_end_io = end_bio_bh_io_sync;
     bio->bi_private = bh;
 
     /* Take care of bh's that straddle the end of the device */
     guard_bio_eod(bio);
 
     if (wbc) {
         wbc_init_bio(wbc, bio);
         wbc_account_cgroup_owner(wbc, bh->b_page, bh->b_size);
     }
 
     submit_bio(bio);
     return 0;
 }
 
 int submit_bh(blk_opf_t opf, struct buffer_head *bh)
 {
     return submit_bh_wbc(opf, bh, NULL);
 }
 EXPORT_SYMBOL(submit_bh);
 
 /**
  * ll_rw_block: low-level access to block devices (DEPRECATED)
  * @opf: block layer request operation and flags.
  * @nr: number of &struct buffer_heads in the array
  * @bhs: array of pointers to &struct buffer_head
  *
  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
  * requests an I/O operation on them, either a %REQ_OP_READ or a %REQ_OP_WRITE.
  * @opf contains flags modifying the detailed I/O behavior, most notably
  * %REQ_RAHEAD.
  *
  * This function drops any buffer that it cannot get a lock on (with the
  * BH_Lock state bit), any buffer that appears to be clean when doing a write
  * request, and any buffer that appears to be up-to-date when doing read
  * request.  Further it marks as clean buffers that are processed for
  * writing (the buffer cache won't assume that they are actually clean
  * until the buffer gets unlocked).
  *
  * ll_rw_block sets b_end_io to simple completion handler that marks
  * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
  * any waiters. 
  *
  * All of the buffers must be for the same device, and must also be a
  * multiple of the current approved size for the device.
  */
 void ll_rw_block(const blk_opf_t opf, int nr, struct buffer_head *bhs[])
 {
     const enum req_op op = opf & REQ_OP_MASK;
     int i;
 
     for (i = 0; i < nr; i++) {
         struct buffer_head *bh = bhs[i];
 
         if (!trylock_buffer(bh))
             continue;
         if (op == REQ_OP_WRITE) {
             if (test_clear_buffer_dirty(bh)) {
                 bh->b_end_io = end_buffer_write_sync;
                 get_bh(bh);
                 submit_bh(opf, bh);
                 continue;
             }
         } else {
             if (!buffer_uptodate(bh)) {
                 bh->b_end_io = end_buffer_read_sync;
                 get_bh(bh);
                 submit_bh(opf, bh);
                 continue;
             }
         }
         unlock_buffer(bh);
     }
 }
 EXPORT_SYMBOL(ll_rw_block);
 
 void write_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags)
 {
     lock_buffer(bh);
     if (!test_clear_buffer_dirty(bh)) {
         unlock_buffer(bh);
         return;
     }
     bh->b_end_io = end_buffer_write_sync;
     get_bh(bh);
     submit_bh(REQ_OP_WRITE | op_flags, bh);
 }
 EXPORT_SYMBOL(write_dirty_buffer);
 
 /*
  * For a data-integrity writeout, we need to wait upon any in-progress I/O
  * and then start new I/O and then wait upon it.  The caller must have a ref on
  * the buffer_head.
  */
 int __sync_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags)
 {
     int ret = 0;
 
     WARN_ON(atomic_read(&bh->b_count) < 1);
     lock_buffer(bh);
     if (test_clear_buffer_dirty(bh)) {
         /*
          * The bh should be mapped, but it might not be if the
          * device was hot-removed. Not much we can do but fail the I/O.
          */
         if (!buffer_mapped(bh)) {
             unlock_buffer(bh);
             return -EIO;
         }
 
         get_bh(bh);
         bh->b_end_io = end_buffer_write_sync;
         ret = submit_bh(REQ_OP_WRITE | op_flags, bh);
         wait_on_buffer(bh);
         if (!ret && !buffer_uptodate(bh))
             ret = -EIO;
     } else {
         unlock_buffer(bh);
     }
     return ret;
 }
 EXPORT_SYMBOL(__sync_dirty_buffer);
 
 int sync_dirty_buffer(struct buffer_head *bh)
 {
     return __sync_dirty_buffer(bh, REQ_SYNC);
 }
 EXPORT_SYMBOL(sync_dirty_buffer);
 
 /*
  * try_to_free_buffers() checks if all the buffers on this particular folio
  * are unused, and releases them if so.
  *
  * Exclusion against try_to_free_buffers may be obtained by either
  * locking the folio or by holding its mapping's private_lock.
  *
  * If the folio is dirty but all the buffers are clean then we need to
  * be sure to mark the folio clean as well.  This is because the folio
  * may be against a block device, and a later reattachment of buffers
  * to a dirty folio will set *all* buffers dirty.  Which would corrupt
  * filesystem data on the same device.
  *
  * The same applies to regular filesystem folios: if all the buffers are
  * clean then we set the folio clean and proceed.  To do that, we require
  * total exclusion from block_dirty_folio().  That is obtained with
  * private_lock.
  *
  * try_to_free_buffers() is non-blocking.
  */
 static inline int buffer_busy(struct buffer_head *bh)
 {
     return atomic_read(&bh->b_count) |
         (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
 }
 
 static bool
 drop_buffers(struct folio *folio, struct buffer_head **buffers_to_free)
 {
     struct buffer_head *head = folio_buffers(folio);
     struct buffer_head *bh;
 
     bh = head;
     do {
         if (buffer_busy(bh))
             goto failed;
         bh = bh->b_this_page;
     } while (bh != head);
 
     do {
         struct buffer_head *next = bh->b_this_page;
 
         if (bh->b_assoc_map)
             __remove_assoc_queue(bh);
         bh = next;
     } while (bh != head);
     *buffers_to_free = head;
     folio_detach_private(folio);
     return true;
 failed:
     return false;
 }
 
 bool try_to_free_buffers(struct folio *folio)
 {
     struct address_space * const mapping = folio->mapping;
     struct buffer_head *buffers_to_free = NULL;
     bool ret = 0;
 
     BUG_ON(!folio_test_locked(folio));
     if (folio_test_writeback(folio))
         return false;
 
     if (mapping == NULL) {      /* can this still happen? */
         ret = drop_buffers(folio, &buffers_to_free);
         goto out;
     }
 
     spin_lock(&mapping->private_lock);
     ret = drop_buffers(folio, &buffers_to_free);
 
     /*
      * If the filesystem writes its buffers by hand (eg ext3)
      * then we can have clean buffers against a dirty folio.  We
      * clean the folio here; otherwise the VM will never notice
      * that the filesystem did any IO at all.
      *
      * Also, during truncate, discard_buffer will have marked all
      * the folio's buffers clean.  We discover that here and clean
      * the folio also.
      *
      * private_lock must be held over this entire operation in order
      * to synchronise against block_dirty_folio and prevent the
      * dirty bit from being lost.
      */
     if (ret)
         folio_cancel_dirty(folio);
     spin_unlock(&mapping->private_lock);
 out:
     if (buffers_to_free) {
         struct buffer_head *bh = buffers_to_free;
 
         do {
             struct buffer_head *next = bh->b_this_page;
             free_buffer_head(bh);
             bh = next;
         } while (bh != buffers_to_free);
     }
     return ret;
 }
 EXPORT_SYMBOL(try_to_free_buffers);
 
 /*
  * Buffer-head allocation
  */
 static struct kmem_cache *bh_cachep __read_mostly;
 
 /*
  * Once the number of bh's in the machine exceeds this level, we start
  * stripping them in writeback.
  */
 static unsigned long max_buffer_heads;
 
 int buffer_heads_over_limit;
 
 struct bh_accounting {
     int nr;         /* Number of live bh's */
     int ratelimit;      /* Limit cacheline bouncing */
 };
 
 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
 
 static void recalc_bh_state(void)
 {
     int i;
     int tot = 0;
 
     if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
         return;
     __this_cpu_write(bh_accounting.ratelimit, 0);
     for_each_online_cpu(i)
         tot += per_cpu(bh_accounting, i).nr;
     buffer_heads_over_limit = (tot > max_buffer_heads);
 }
 
 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
 {
     struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
     if (ret) {
         INIT_LIST_HEAD(&ret->b_assoc_buffers);
         spin_lock_init(&ret->b_uptodate_lock);
         preempt_disable();
         __this_cpu_inc(bh_accounting.nr);
         recalc_bh_state();
         preempt_enable();
     }
     return ret;
 }
 EXPORT_SYMBOL(alloc_buffer_head);
 
 void free_buffer_head(struct buffer_head *bh)
 {
     BUG_ON(!list_empty(&bh->b_assoc_buffers));
     kmem_cache_free(bh_cachep, bh);
     preempt_disable();
     __this_cpu_dec(bh_accounting.nr);
     recalc_bh_state();
     preempt_enable();
 }
 EXPORT_SYMBOL(free_buffer_head);
 
 static int buffer_exit_cpu_dead(unsigned int cpu)
 {
     int i;
     struct bh_lru *b = &per_cpu(bh_lrus, cpu);
 
     for (i = 0; i < BH_LRU_SIZE; i++) {
         brelse(b->bhs[i]);
         b->bhs[i] = NULL;
     }
     this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
     per_cpu(bh_accounting, cpu).nr = 0;
     return 0;
 }
 
 /**
  * bh_uptodate_or_lock - Test whether the buffer is uptodate
  * @bh: struct buffer_head
  *
  * Return true if the buffer is up-to-date and false,
  * with the buffer locked, if not.
  */
 int bh_uptodate_or_lock(struct buffer_head *bh)
 {
     if (!buffer_uptodate(bh)) {
         lock_buffer(bh);
         if (!buffer_uptodate(bh))
             return 0;
         unlock_buffer(bh);
     }
     return 1;
 }
 EXPORT_SYMBOL(bh_uptodate_or_lock);
 
 /**
  * bh_submit_read - Submit a locked buffer for reading
  * @bh: struct buffer_head
  *
  * Returns zero on success and -EIO on error.
  */
 int bh_submit_read(struct buffer_head *bh)
 {
     BUG_ON(!buffer_locked(bh));
 
     if (buffer_uptodate(bh)) {
         unlock_buffer(bh);
         return 0;
     }
 
     get_bh(bh);
     bh->b_end_io = end_buffer_read_sync;
     submit_bh(REQ_OP_READ, bh);
     wait_on_buffer(bh);
     if (buffer_uptodate(bh))
         return 0;
     return -EIO;
 }
 EXPORT_SYMBOL(bh_submit_read);
 
 void __init buffer_init(void)
 {
     unsigned long nrpages;
     int ret;
 
     bh_cachep = kmem_cache_create("buffer_head",
             sizeof(struct buffer_head), 0,
                 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
                 SLAB_MEM_SPREAD),
                 NULL);
 
     /*
      * Limit the bh occupancy to 10% of ZONE_NORMAL
      */
     nrpages = (nr_free_buffer_pages() * 10) / 100;
     max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
     ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
                     NULL, buffer_exit_cpu_dead);
     WARN_ON(ret < 0);
 }