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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  fs/libfs.c
  *  Library for filesystems writers.
  */
 
 #include <linux/blkdev.h>
 #include <linux/export.h>
 #include <linux/pagemap.h>
 #include <linux/slab.h>
 #include <linux/cred.h>
 #include <linux/mount.h>
 #include <linux/vfs.h>
 #include <linux/quotaops.h>
 #include <linux/mutex.h>
 #include <linux/namei.h>
 #include <linux/exportfs.h>
 #include <linux/writeback.h>
 #include <linux/buffer_head.h> /* sync_mapping_buffers */
 #include <linux/fs_context.h>
 #include <linux/pseudo_fs.h>
 #include <linux/fsnotify.h>
 #include <linux/unicode.h>
 #include <linux/fscrypt.h>
 
 #include <linux/uaccess.h>
 
 #include "internal.h"
 
 int simple_getattr(struct user_namespace *mnt_userns, const struct path *path,
            struct kstat *stat, u32 request_mask,
            unsigned int query_flags)
 {
     struct inode *inode = d_inode(path->dentry);
     generic_fillattr(&init_user_ns, inode, stat);
     stat->blocks = inode->i_mapping->nrpages << (PAGE_SHIFT - 9);
     return 0;
 }
 EXPORT_SYMBOL(simple_getattr);
 
 int simple_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
     buf->f_type = dentry->d_sb->s_magic;
     buf->f_bsize = PAGE_SIZE;
     buf->f_namelen = NAME_MAX;
     return 0;
 }
 EXPORT_SYMBOL(simple_statfs);
 
 /*
  * Retaining negative dentries for an in-memory filesystem just wastes
  * memory and lookup time: arrange for them to be deleted immediately.
  */
 int always_delete_dentry(const struct dentry *dentry)
 {
     return 1;
 }
 EXPORT_SYMBOL(always_delete_dentry);
 
 const struct dentry_operations simple_dentry_operations = {
     .d_delete = always_delete_dentry,
 };
 EXPORT_SYMBOL(simple_dentry_operations);
 
 /*
  * Lookup the data. This is trivial - if the dentry didn't already
  * exist, we know it is negative.  Set d_op to delete negative dentries.
  */
 struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 {
     if (dentry->d_name.len > NAME_MAX)
         return ERR_PTR(-ENAMETOOLONG);
     if (!dentry->d_sb->s_d_op)
         d_set_d_op(dentry, &simple_dentry_operations);
     d_add(dentry, NULL);
     return NULL;
 }
 EXPORT_SYMBOL(simple_lookup);
 
 int dcache_dir_open(struct inode *inode, struct file *file)
 {
     file->private_data = d_alloc_cursor(file->f_path.dentry);
 
     return file->private_data ? 0 : -ENOMEM;
 }
 EXPORT_SYMBOL(dcache_dir_open);
 
 int dcache_dir_close(struct inode *inode, struct file *file)
 {
     dput(file->private_data);
     return 0;
 }
 EXPORT_SYMBOL(dcache_dir_close);
 
 /* parent is locked at least shared */
 /*
  * Returns an element of siblings' list.
  * We are looking for <count>th positive after <p>; if
  * found, dentry is grabbed and returned to caller.
  * If no such element exists, NULL is returned.
  */
 static struct dentry *scan_positives(struct dentry *cursor,
                     struct list_head *p,
                     loff_t count,
                     struct dentry *last)
 {
     struct dentry *dentry = cursor->d_parent, *found = NULL;
 
     spin_lock(&dentry->d_lock);
     while ((p = p->next) != &dentry->d_subdirs) {
         struct dentry *d = list_entry(p, struct dentry, d_child);
         // we must at least skip cursors, to avoid livelocks
         if (d->d_flags & DCACHE_DENTRY_CURSOR)
             continue;
         if (simple_positive(d) && !--count) {
             spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
             if (simple_positive(d))
                 found = dget_dlock(d);
             spin_unlock(&d->d_lock);
             if (likely(found))
                 break;
             count = 1;
         }
         if (need_resched()) {
             list_move(&cursor->d_child, p);
             p = &cursor->d_child;
             spin_unlock(&dentry->d_lock);
             cond_resched();
             spin_lock(&dentry->d_lock);
         }
     }
     spin_unlock(&dentry->d_lock);
     dput(last);
     return found;
 }
 
 loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
 {
     struct dentry *dentry = file->f_path.dentry;
     switch (whence) {
         case 1:
             offset += file->f_pos;
             fallthrough;
         case 0:
             if (offset >= 0)
                 break;
             fallthrough;
         default:
             return -EINVAL;
     }
     if (offset != file->f_pos) {
         struct dentry *cursor = file->private_data;
         struct dentry *to = NULL;
 
         inode_lock_shared(dentry->d_inode);
 
         if (offset > 2)
             to = scan_positives(cursor, &dentry->d_subdirs,
                         offset - 2, NULL);
         spin_lock(&dentry->d_lock);
         if (to)
             list_move(&cursor->d_child, &to->d_child);
         else
             list_del_init(&cursor->d_child);
         spin_unlock(&dentry->d_lock);
         dput(to);
 
         file->f_pos = offset;
 
         inode_unlock_shared(dentry->d_inode);
     }
     return offset;
 }
 EXPORT_SYMBOL(dcache_dir_lseek);
 
 /* Relationship between i_mode and the DT_xxx types */
 static inline unsigned char dt_type(struct inode *inode)
 {
     return (inode->i_mode >> 12) & 15;
 }
 
 /*
  * Directory is locked and all positive dentries in it are safe, since
  * for ramfs-type trees they can't go away without unlink() or rmdir(),
  * both impossible due to the lock on directory.
  */
 
 int dcache_readdir(struct file *file, struct dir_context *ctx)
 {
     struct dentry *dentry = file->f_path.dentry;
     struct dentry *cursor = file->private_data;
     struct list_head *anchor = &dentry->d_subdirs;
     struct dentry *next = NULL;
     struct list_head *p;
 
     if (!dir_emit_dots(file, ctx))
         return 0;
 
     if (ctx->pos == 2)
         p = anchor;
     else if (!list_empty(&cursor->d_child))
         p = &cursor->d_child;
     else
         return 0;
 
     while ((next = scan_positives(cursor, p, 1, next)) != NULL) {
         if (!dir_emit(ctx, next->d_name.name, next->d_name.len,
                   d_inode(next)->i_ino, dt_type(d_inode(next))))
             break;
         ctx->pos++;
         p = &next->d_child;
     }
     spin_lock(&dentry->d_lock);
     if (next)
         list_move_tail(&cursor->d_child, &next->d_child);
     else
         list_del_init(&cursor->d_child);
     spin_unlock(&dentry->d_lock);
     dput(next);
 
     return 0;
 }
 EXPORT_SYMBOL(dcache_readdir);
 
 ssize_t generic_read_dir(struct file *filp, char __user *buf, size_t siz, loff_t *ppos)
 {
     return -EISDIR;
 }
 EXPORT_SYMBOL(generic_read_dir);
 
 const struct file_operations simple_dir_operations = {
     .open       = dcache_dir_open,
     .release    = dcache_dir_close,
     .llseek     = dcache_dir_lseek,
     .read       = generic_read_dir,
     .iterate_shared = dcache_readdir,
     .fsync      = noop_fsync,
 };
 EXPORT_SYMBOL(simple_dir_operations);
 
 const struct inode_operations simple_dir_inode_operations = {
     .lookup     = simple_lookup,
 };
 EXPORT_SYMBOL(simple_dir_inode_operations);
 
 static struct dentry *find_next_child(struct dentry *parent, struct dentry *prev)
 {
     struct dentry *child = NULL;
     struct list_head *p = prev ? &prev->d_child : &parent->d_subdirs;
 
     spin_lock(&parent->d_lock);
     while ((p = p->next) != &parent->d_subdirs) {
         struct dentry *d = container_of(p, struct dentry, d_child);
         if (simple_positive(d)) {
             spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
             if (simple_positive(d))
                 child = dget_dlock(d);
             spin_unlock(&d->d_lock);
             if (likely(child))
                 break;
         }
     }
     spin_unlock(&parent->d_lock);
     dput(prev);
     return child;
 }
 
 void simple_recursive_removal(struct dentry *dentry,
                               void (*callback)(struct dentry *))
 {
     struct dentry *this = dget(dentry);
     while (true) {
         struct dentry *victim = NULL, *child;
         struct inode *inode = this->d_inode;
 
         inode_lock(inode);
         if (d_is_dir(this))
             inode->i_flags |= S_DEAD;
         while ((child = find_next_child(this, victim)) == NULL) {
             // kill and ascend
             // update metadata while it's still locked
             inode->i_ctime = current_time(inode);
             clear_nlink(inode);
             inode_unlock(inode);
             victim = this;
             this = this->d_parent;
             inode = this->d_inode;
             inode_lock(inode);
             if (simple_positive(victim)) {
                 d_invalidate(victim);   // avoid lost mounts
                 if (d_is_dir(victim))
                     fsnotify_rmdir(inode, victim);
                 else
                     fsnotify_unlink(inode, victim);
                 if (callback)
                     callback(victim);
                 dput(victim);       // unpin it
             }
             if (victim == dentry) {
                 inode->i_ctime = inode->i_mtime =
                     current_time(inode);
                 if (d_is_dir(dentry))
                     drop_nlink(inode);
                 inode_unlock(inode);
                 dput(dentry);
                 return;
             }
         }
         inode_unlock(inode);
         this = child;
     }
 }
 EXPORT_SYMBOL(simple_recursive_removal);
 
 static const struct super_operations simple_super_operations = {
     .statfs     = simple_statfs,
 };
 
 static int pseudo_fs_fill_super(struct super_block *s, struct fs_context *fc)
 {
     struct pseudo_fs_context *ctx = fc->fs_private;
     struct inode *root;
 
     s->s_maxbytes = MAX_LFS_FILESIZE;
     s->s_blocksize = PAGE_SIZE;
     s->s_blocksize_bits = PAGE_SHIFT;
     s->s_magic = ctx->magic;
     s->s_op = ctx->ops ?: &simple_super_operations;
     s->s_xattr = ctx->xattr;
     s->s_time_gran = 1;
     root = new_inode(s);
     if (!root)
         return -ENOMEM;
 
     /*
      * since this is the first inode, make it number 1. New inodes created
      * after this must take care not to collide with it (by passing
      * max_reserved of 1 to iunique).
      */
     root->i_ino = 1;
     root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
     root->i_atime = root->i_mtime = root->i_ctime = current_time(root);
     s->s_root = d_make_root(root);
     if (!s->s_root)
         return -ENOMEM;
     s->s_d_op = ctx->dops;
     return 0;
 }
 
 static int pseudo_fs_get_tree(struct fs_context *fc)
 {
     return get_tree_nodev(fc, pseudo_fs_fill_super);
 }
 
 static void pseudo_fs_free(struct fs_context *fc)
 {
     kfree(fc->fs_private);
 }
 
 static const struct fs_context_operations pseudo_fs_context_ops = {
     .free       = pseudo_fs_free,
     .get_tree   = pseudo_fs_get_tree,
 };
 
 /*
  * Common helper for pseudo-filesystems (sockfs, pipefs, bdev - stuff that
  * will never be mountable)
  */
 struct pseudo_fs_context *init_pseudo(struct fs_context *fc,
                     unsigned long magic)
 {
     struct pseudo_fs_context *ctx;
 
     ctx = kzalloc(sizeof(struct pseudo_fs_context), GFP_KERNEL);
     if (likely(ctx)) {
         ctx->magic = magic;
         fc->fs_private = ctx;
         fc->ops = &pseudo_fs_context_ops;
         fc->sb_flags |= SB_NOUSER;
         fc->global = true;
     }
     return ctx;
 }
 EXPORT_SYMBOL(init_pseudo);
 
 int simple_open(struct inode *inode, struct file *file)
 {
     if (inode->i_private)
         file->private_data = inode->i_private;
     return 0;
 }
 EXPORT_SYMBOL(simple_open);
 
 int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
 {
     struct inode *inode = d_inode(old_dentry);
 
     inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
     inc_nlink(inode);
     ihold(inode);
     dget(dentry);
     d_instantiate(dentry, inode);
     return 0;
 }
 EXPORT_SYMBOL(simple_link);
 
 int simple_empty(struct dentry *dentry)
 {
     struct dentry *child;
     int ret = 0;
 
     spin_lock(&dentry->d_lock);
     list_for_each_entry(child, &dentry->d_subdirs, d_child) {
         spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
         if (simple_positive(child)) {
             spin_unlock(&child->d_lock);
             goto out;
         }
         spin_unlock(&child->d_lock);
     }
     ret = 1;
 out:
     spin_unlock(&dentry->d_lock);
     return ret;
 }
 EXPORT_SYMBOL(simple_empty);
 
 int simple_unlink(struct inode *dir, struct dentry *dentry)
 {
     struct inode *inode = d_inode(dentry);
 
     inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
     drop_nlink(inode);
     dput(dentry);
     return 0;
 }
 EXPORT_SYMBOL(simple_unlink);
 
 int simple_rmdir(struct inode *dir, struct dentry *dentry)
 {
     if (!simple_empty(dentry))
         return -ENOTEMPTY;
 
     drop_nlink(d_inode(dentry));
     simple_unlink(dir, dentry);
     drop_nlink(dir);
     return 0;
 }
 EXPORT_SYMBOL(simple_rmdir);
 
 int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
                struct inode *new_dir, struct dentry *new_dentry)
 {
     bool old_is_dir = d_is_dir(old_dentry);
     bool new_is_dir = d_is_dir(new_dentry);
 
     if (old_dir != new_dir && old_is_dir != new_is_dir) {
         if (old_is_dir) {
             drop_nlink(old_dir);
             inc_nlink(new_dir);
         } else {
             drop_nlink(new_dir);
             inc_nlink(old_dir);
         }
     }
     old_dir->i_ctime = old_dir->i_mtime =
     new_dir->i_ctime = new_dir->i_mtime =
     d_inode(old_dentry)->i_ctime =
     d_inode(new_dentry)->i_ctime = current_time(old_dir);
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(simple_rename_exchange);
 
 int simple_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
           struct dentry *old_dentry, struct inode *new_dir,
           struct dentry *new_dentry, unsigned int flags)
 {
     struct inode *inode = d_inode(old_dentry);
     int they_are_dirs = d_is_dir(old_dentry);
 
     if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
         return -EINVAL;
 
     if (flags & RENAME_EXCHANGE)
         return simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
 
     if (!simple_empty(new_dentry))
         return -ENOTEMPTY;
 
     if (d_really_is_positive(new_dentry)) {
         simple_unlink(new_dir, new_dentry);
         if (they_are_dirs) {
             drop_nlink(d_inode(new_dentry));
             drop_nlink(old_dir);
         }
     } else if (they_are_dirs) {
         drop_nlink(old_dir);
         inc_nlink(new_dir);
     }
 
     old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
         new_dir->i_mtime = inode->i_ctime = current_time(old_dir);
 
     return 0;
 }
 EXPORT_SYMBOL(simple_rename);
 
 /**
  * simple_setattr - setattr for simple filesystem
  * @mnt_userns: user namespace of the target mount
  * @dentry: dentry
  * @iattr: iattr structure
  *
  * Returns 0 on success, -error on failure.
  *
  * simple_setattr is a simple ->setattr implementation without a proper
  * implementation of size changes.
  *
  * It can either be used for in-memory filesystems or special files
  * on simple regular filesystems.  Anything that needs to change on-disk
  * or wire state on size changes needs its own setattr method.
  */
 int simple_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
            struct iattr *iattr)
 {
     struct inode *inode = d_inode(dentry);
     int error;
 
     error = setattr_prepare(mnt_userns, dentry, iattr);
     if (error)
         return error;
 
     if (iattr->ia_valid & ATTR_SIZE)
         truncate_setsize(inode, iattr->ia_size);
     setattr_copy(mnt_userns, inode, iattr);
     mark_inode_dirty(inode);
     return 0;
 }
 EXPORT_SYMBOL(simple_setattr);
 
 static int simple_read_folio(struct file *file, struct folio *folio)
 {
     folio_zero_range(folio, 0, folio_size(folio));
     flush_dcache_folio(folio);
     folio_mark_uptodate(folio);
     folio_unlock(folio);
     return 0;
 }
 
 int simple_write_begin(struct file *file, struct address_space *mapping,
             loff_t pos, unsigned len,
             struct page **pagep, void **fsdata)
 {
     struct page *page;
     pgoff_t index;
 
     index = pos >> PAGE_SHIFT;
 
     page = grab_cache_page_write_begin(mapping, index);
     if (!page)
         return -ENOMEM;
 
     *pagep = page;
 
     if (!PageUptodate(page) && (len != PAGE_SIZE)) {
         unsigned from = pos & (PAGE_SIZE - 1);
 
         zero_user_segments(page, 0, from, from + len, PAGE_SIZE);
     }
     return 0;
 }
 EXPORT_SYMBOL(simple_write_begin);
 
 /**
  * simple_write_end - .write_end helper for non-block-device FSes
  * @file: See .write_end of address_space_operations
  * @mapping:        "
  * @pos:        "
  * @len:        "
  * @copied:         "
  * @page:       "
  * @fsdata:         "
  *
  * simple_write_end does the minimum needed for updating a page after writing is
  * done. It has the same API signature as the .write_end of
  * address_space_operations vector. So it can just be set onto .write_end for
  * FSes that don't need any other processing. i_mutex is assumed to be held.
  * Block based filesystems should use generic_write_end().
  * NOTE: Even though i_size might get updated by this function, mark_inode_dirty
  * is not called, so a filesystem that actually does store data in .write_inode
  * should extend on what's done here with a call to mark_inode_dirty() in the
  * case that i_size has changed.
  *
  * Use *ONLY* with simple_read_folio()
  */
 static int simple_write_end(struct file *file, struct address_space *mapping,
             loff_t pos, unsigned len, unsigned copied,
             struct page *page, void *fsdata)
 {
     struct inode *inode = page->mapping->host;
     loff_t last_pos = pos + copied;
 
     /* zero the stale part of the page if we did a short copy */
     if (!PageUptodate(page)) {
         if (copied < len) {
             unsigned from = pos & (PAGE_SIZE - 1);
 
             zero_user(page, from + copied, len - copied);
         }
         SetPageUptodate(page);
     }
     /*
      * No need to use i_size_read() here, the i_size
      * cannot change under us because we hold the i_mutex.
      */
     if (last_pos > inode->i_size)
         i_size_write(inode, last_pos);
 
     set_page_dirty(page);
     unlock_page(page);
     put_page(page);
 
     return copied;
 }
 
 /*
  * Provides ramfs-style behavior: data in the pagecache, but no writeback.
  */
 const struct address_space_operations ram_aops = {
     .read_folio = simple_read_folio,
     .write_begin    = simple_write_begin,
     .write_end  = simple_write_end,
     .dirty_folio    = noop_dirty_folio,
 };
 EXPORT_SYMBOL(ram_aops);
 
 /*
  * the inodes created here are not hashed. If you use iunique to generate
  * unique inode values later for this filesystem, then you must take care
  * to pass it an appropriate max_reserved value to avoid collisions.
  */
 int simple_fill_super(struct super_block *s, unsigned long magic,
               const struct tree_descr *files)
 {
     struct inode *inode;
     struct dentry *root;
     struct dentry *dentry;
     int i;
 
     s->s_blocksize = PAGE_SIZE;
     s->s_blocksize_bits = PAGE_SHIFT;
     s->s_magic = magic;
     s->s_op = &simple_super_operations;
     s->s_time_gran = 1;
 
     inode = new_inode(s);
     if (!inode)
         return -ENOMEM;
     /*
      * because the root inode is 1, the files array must not contain an
      * entry at index 1
      */
     inode->i_ino = 1;
     inode->i_mode = S_IFDIR | 0755;
     inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
     inode->i_op = &simple_dir_inode_operations;
     inode->i_fop = &simple_dir_operations;
     set_nlink(inode, 2);
     root = d_make_root(inode);
     if (!root)
         return -ENOMEM;
     for (i = 0; !files->name || files->name[0]; i++, files++) {
         if (!files->name)
             continue;
 
         /* warn if it tries to conflict with the root inode */
         if (unlikely(i == 1))
             printk(KERN_WARNING "%s: %s passed in a files array"
                 "with an index of 1!\n", __func__,
                 s->s_type->name);
 
         dentry = d_alloc_name(root, files->name);
         if (!dentry)
             goto out;
         inode = new_inode(s);
         if (!inode) {
             dput(dentry);
             goto out;
         }
         inode->i_mode = S_IFREG | files->mode;
         inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
         inode->i_fop = files->ops;
         inode->i_ino = i;
         d_add(dentry, inode);
     }
     s->s_root = root;
     return 0;
 out:
     d_genocide(root);
     shrink_dcache_parent(root);
     dput(root);
     return -ENOMEM;
 }
 EXPORT_SYMBOL(simple_fill_super);
 
 static DEFINE_SPINLOCK(pin_fs_lock);
 
 int simple_pin_fs(struct file_system_type *type, struct vfsmount **mount, int *count)
 {
     struct vfsmount *mnt = NULL;
     spin_lock(&pin_fs_lock);
     if (unlikely(!*mount)) {
         spin_unlock(&pin_fs_lock);
         mnt = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL);
         if (IS_ERR(mnt))
             return PTR_ERR(mnt);
         spin_lock(&pin_fs_lock);
         if (!*mount)
             *mount = mnt;
     }
     mntget(*mount);
     ++*count;
     spin_unlock(&pin_fs_lock);
     mntput(mnt);
     return 0;
 }
 EXPORT_SYMBOL(simple_pin_fs);
 
 void simple_release_fs(struct vfsmount **mount, int *count)
 {
     struct vfsmount *mnt;
     spin_lock(&pin_fs_lock);
     mnt = *mount;
     if (!--*count)
         *mount = NULL;
     spin_unlock(&pin_fs_lock);
     mntput(mnt);
 }
 EXPORT_SYMBOL(simple_release_fs);
 
 /**
  * simple_read_from_buffer - copy data from the buffer to user space
  * @to: the user space buffer to read to
  * @count: the maximum number of bytes to read
  * @ppos: the current position in the buffer
  * @from: the buffer to read from
  * @available: the size of the buffer
  *
  * The simple_read_from_buffer() function reads up to @count bytes from the
  * buffer @from at offset @ppos into the user space address starting at @to.
  *
  * On success, the number of bytes read is returned and the offset @ppos is
  * advanced by this number, or negative value is returned on error.
  **/
 ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
                 const void *from, size_t available)
 {
     loff_t pos = *ppos;
     size_t ret;
 
     if (pos < 0)
         return -EINVAL;
     if (pos >= available || !count)
         return 0;
     if (count > available - pos)
         count = available - pos;
     ret = copy_to_user(to, from + pos, count);
     if (ret == count)
         return -EFAULT;
     count -= ret;
     *ppos = pos + count;
     return count;
 }
 EXPORT_SYMBOL(simple_read_from_buffer);
 
 /**
  * simple_write_to_buffer - copy data from user space to the buffer
  * @to: the buffer to write to
  * @available: the size of the buffer
  * @ppos: the current position in the buffer
  * @from: the user space buffer to read from
  * @count: the maximum number of bytes to read
  *
  * The simple_write_to_buffer() function reads up to @count bytes from the user
  * space address starting at @from into the buffer @to at offset @ppos.
  *
  * On success, the number of bytes written is returned and the offset @ppos is
  * advanced by this number, or negative value is returned on error.
  **/
 ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
         const void __user *from, size_t count)
 {
     loff_t pos = *ppos;
     size_t res;
 
     if (pos < 0)
         return -EINVAL;
     if (pos >= available || !count)
         return 0;
     if (count > available - pos)
         count = available - pos;
     res = copy_from_user(to + pos, from, count);
     if (res == count)
         return -EFAULT;
     count -= res;
     *ppos = pos + count;
     return count;
 }
 EXPORT_SYMBOL(simple_write_to_buffer);
 
 /**
  * memory_read_from_buffer - copy data from the buffer
  * @to: the kernel space buffer to read to
  * @count: the maximum number of bytes to read
  * @ppos: the current position in the buffer
  * @from: the buffer to read from
  * @available: the size of the buffer
  *
  * The memory_read_from_buffer() function reads up to @count bytes from the
  * buffer @from at offset @ppos into the kernel space address starting at @to.
  *
  * On success, the number of bytes read is returned and the offset @ppos is
  * advanced by this number, or negative value is returned on error.
  **/
 ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
                 const void *from, size_t available)
 {
     loff_t pos = *ppos;
 
     if (pos < 0)
         return -EINVAL;
     if (pos >= available)
         return 0;
     if (count > available - pos)
         count = available - pos;
     memcpy(to, from + pos, count);
     *ppos = pos + count;
 
     return count;
 }
 EXPORT_SYMBOL(memory_read_from_buffer);
 
 /*
  * Transaction based IO.
  * The file expects a single write which triggers the transaction, and then
  * possibly a read which collects the result - which is stored in a
  * file-local buffer.
  */
 
 void simple_transaction_set(struct file *file, size_t n)
 {
     struct simple_transaction_argresp *ar = file->private_data;
 
     BUG_ON(n > SIMPLE_TRANSACTION_LIMIT);
 
     /*
      * The barrier ensures that ar->size will really remain zero until
      * ar->data is ready for reading.
      */
     smp_mb();
     ar->size = n;
 }
 EXPORT_SYMBOL(simple_transaction_set);
 
 char *simple_transaction_get(struct file *file, const char __user *buf, size_t size)
 {
     struct simple_transaction_argresp *ar;
     static DEFINE_SPINLOCK(simple_transaction_lock);
 
     if (size > SIMPLE_TRANSACTION_LIMIT - 1)
         return ERR_PTR(-EFBIG);
 
     ar = (struct simple_transaction_argresp *)get_zeroed_page(GFP_KERNEL);
     if (!ar)
         return ERR_PTR(-ENOMEM);
 
     spin_lock(&simple_transaction_lock);
 
     /* only one write allowed per open */
     if (file->private_data) {
         spin_unlock(&simple_transaction_lock);
         free_page((unsigned long)ar);
         return ERR_PTR(-EBUSY);
     }
 
     file->private_data = ar;
 
     spin_unlock(&simple_transaction_lock);
 
     if (copy_from_user(ar->data, buf, size))
         return ERR_PTR(-EFAULT);
 
     return ar->data;
 }
 EXPORT_SYMBOL(simple_transaction_get);
 
 ssize_t simple_transaction_read(struct file *file, char __user *buf, size_t size, loff_t *pos)
 {
     struct simple_transaction_argresp *ar = file->private_data;
 
     if (!ar)
         return 0;
     return simple_read_from_buffer(buf, size, pos, ar->data, ar->size);
 }
 EXPORT_SYMBOL(simple_transaction_read);
 
 int simple_transaction_release(struct inode *inode, struct file *file)
 {
     free_page((unsigned long)file->private_data);
     return 0;
 }
 EXPORT_SYMBOL(simple_transaction_release);
 
 /* Simple attribute files */
 
 struct simple_attr {
     int (*get)(void *, u64 *);
     int (*set)(void *, u64);
     char get_buf[24];   /* enough to store a u64 and "\n\0" */
     char set_buf[24];
     void *data;
     const char *fmt;    /* format for read operation */
     struct mutex mutex; /* protects access to these buffers */
 };
 
 /* simple_attr_open is called by an actual attribute open file operation
  * to set the attribute specific access operations. */
 int simple_attr_open(struct inode *inode, struct file *file,
              int (*get)(void *, u64 *), int (*set)(void *, u64),
              const char *fmt)
 {
     struct simple_attr *attr;
 
     attr = kzalloc(sizeof(*attr), GFP_KERNEL);
     if (!attr)
         return -ENOMEM;
 
     attr->get = get;
     attr->set = set;
     attr->data = inode->i_private;
     attr->fmt = fmt;
     mutex_init(&attr->mutex);
 
     file->private_data = attr;
 
     return nonseekable_open(inode, file);
 }
 EXPORT_SYMBOL_GPL(simple_attr_open);
 
 int simple_attr_release(struct inode *inode, struct file *file)
 {
     kfree(file->private_data);
     return 0;
 }
 EXPORT_SYMBOL_GPL(simple_attr_release); /* GPL-only?  This?  Really? */
 
 /* read from the buffer that is filled with the get function */
 ssize_t simple_attr_read(struct file *file, char __user *buf,
              size_t len, loff_t *ppos)
 {
     struct simple_attr *attr;
     size_t size;
     ssize_t ret;
 
     attr = file->private_data;
 
     if (!attr->get)
         return -EACCES;
 
     ret = mutex_lock_interruptible(&attr->mutex);
     if (ret)
         return ret;
 
     if (*ppos && attr->get_buf[0]) {
         /* continued read */
         size = strlen(attr->get_buf);
     } else {
         /* first read */
         u64 val;
         ret = attr->get(attr->data, &val);
         if (ret)
             goto out;
 
         size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
                  attr->fmt, (unsigned long long)val);
     }
 
     ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
 out:
     mutex_unlock(&attr->mutex);
     return ret;
 }
 EXPORT_SYMBOL_GPL(simple_attr_read);
 
 /* interpret the buffer as a number to call the set function with */
 ssize_t simple_attr_write(struct file *file, const char __user *buf,
               size_t len, loff_t *ppos)
 {
     struct simple_attr *attr;
     unsigned long long val;
     size_t size;
     ssize_t ret;
 
     attr = file->private_data;
     if (!attr->set)
         return -EACCES;
 
     ret = mutex_lock_interruptible(&attr->mutex);
     if (ret)
         return ret;
 
     ret = -EFAULT;
     size = min(sizeof(attr->set_buf) - 1, len);
     if (copy_from_user(attr->set_buf, buf, size))
         goto out;
 
     attr->set_buf[size] = '\0';
     ret = kstrtoull(attr->set_buf, 0, &val);
     if (ret)
         goto out;
     ret = attr->set(attr->data, val);
     if (ret == 0)
         ret = len; /* on success, claim we got the whole input */
 out:
     mutex_unlock(&attr->mutex);
     return ret;
 }
 EXPORT_SYMBOL_GPL(simple_attr_write);
 
 /**
  * generic_fh_to_dentry - generic helper for the fh_to_dentry export operation
  * @sb:     filesystem to do the file handle conversion on
  * @fid:    file handle to convert
  * @fh_len: length of the file handle in bytes
  * @fh_type:    type of file handle
  * @get_inode:  filesystem callback to retrieve inode
  *
  * This function decodes @fid as long as it has one of the well-known
  * Linux filehandle types and calls @get_inode on it to retrieve the
  * inode for the object specified in the file handle.
  */
 struct dentry *generic_fh_to_dentry(struct super_block *sb, struct fid *fid,
         int fh_len, int fh_type, struct inode *(*get_inode)
             (struct super_block *sb, u64 ino, u32 gen))
 {
     struct inode *inode = NULL;
 
     if (fh_len < 2)
         return NULL;
 
     switch (fh_type) {
     case FILEID_INO32_GEN:
     case FILEID_INO32_GEN_PARENT:
         inode = get_inode(sb, fid->i32.ino, fid->i32.gen);
         break;
     }
 
     return d_obtain_alias(inode);
 }
 EXPORT_SYMBOL_GPL(generic_fh_to_dentry);
 
 /**
  * generic_fh_to_parent - generic helper for the fh_to_parent export operation
  * @sb:     filesystem to do the file handle conversion on
  * @fid:    file handle to convert
  * @fh_len: length of the file handle in bytes
  * @fh_type:    type of file handle
  * @get_inode:  filesystem callback to retrieve inode
  *
  * This function decodes @fid as long as it has one of the well-known
  * Linux filehandle types and calls @get_inode on it to retrieve the
  * inode for the _parent_ object specified in the file handle if it
  * is specified in the file handle, or NULL otherwise.
  */
 struct dentry *generic_fh_to_parent(struct super_block *sb, struct fid *fid,
         int fh_len, int fh_type, struct inode *(*get_inode)
             (struct super_block *sb, u64 ino, u32 gen))
 {
     struct inode *inode = NULL;
 
     if (fh_len <= 2)
         return NULL;
 
     switch (fh_type) {
     case FILEID_INO32_GEN_PARENT:
         inode = get_inode(sb, fid->i32.parent_ino,
                   (fh_len > 3 ? fid->i32.parent_gen : 0));
         break;
     }
 
     return d_obtain_alias(inode);
 }
 EXPORT_SYMBOL_GPL(generic_fh_to_parent);
 
 /**
  * __generic_file_fsync - generic fsync implementation for simple filesystems
  *
  * @file:   file to synchronize
  * @start:  start offset in bytes
  * @end:    end offset in bytes (inclusive)
  * @datasync:   only synchronize essential metadata if true
  *
  * This is a generic implementation of the fsync method for simple
  * filesystems which track all non-inode metadata in the buffers list
  * hanging off the address_space structure.
  */
 int __generic_file_fsync(struct file *file, loff_t start, loff_t end,
                  int datasync)
 {
     struct inode *inode = file->f_mapping->host;
     int err;
     int ret;
 
     err = file_write_and_wait_range(file, start, end);
     if (err)
         return err;
 
     inode_lock(inode);
     ret = sync_mapping_buffers(inode->i_mapping);
     if (!(inode->i_state & I_DIRTY_ALL))
         goto out;
     if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
         goto out;
 
     err = sync_inode_metadata(inode, 1);
     if (ret == 0)
         ret = err;
 
 out:
     inode_unlock(inode);
     /* check and advance again to catch errors after syncing out buffers */
     err = file_check_and_advance_wb_err(file);
     if (ret == 0)
         ret = err;
     return ret;
 }
 EXPORT_SYMBOL(__generic_file_fsync);
 
 /**
  * generic_file_fsync - generic fsync implementation for simple filesystems
  *          with flush
  * @file:   file to synchronize
  * @start:  start offset in bytes
  * @end:    end offset in bytes (inclusive)
  * @datasync:   only synchronize essential metadata if true
  *
  */
 
 int generic_file_fsync(struct file *file, loff_t start, loff_t end,
                int datasync)
 {
     struct inode *inode = file->f_mapping->host;
     int err;
 
     err = __generic_file_fsync(file, start, end, datasync);
     if (err)
         return err;
     return blkdev_issue_flush(inode->i_sb->s_bdev);
 }
 EXPORT_SYMBOL(generic_file_fsync);
 
 /**
  * generic_check_addressable - Check addressability of file system
  * @blocksize_bits: log of file system block size
  * @num_blocks:     number of blocks in file system
  *
  * Determine whether a file system with @num_blocks blocks (and a
  * block size of 2**@blocksize_bits) is addressable by the sector_t
  * and page cache of the system.  Return 0 if so and -EFBIG otherwise.
  */
 int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
 {
     u64 last_fs_block = num_blocks - 1;
     u64 last_fs_page =
         last_fs_block >> (PAGE_SHIFT - blocksize_bits);
 
     if (unlikely(num_blocks == 0))
         return 0;
 
     if ((blocksize_bits < 9) || (blocksize_bits > PAGE_SHIFT))
         return -EINVAL;
 
     if ((last_fs_block > (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
         (last_fs_page > (pgoff_t)(~0ULL))) {
         return -EFBIG;
     }
     return 0;
 }
 EXPORT_SYMBOL(generic_check_addressable);
 
 /*
  * No-op implementation of ->fsync for in-memory filesystems.
  */
 int noop_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 {
     return 0;
 }
 EXPORT_SYMBOL(noop_fsync);
 
 ssize_t noop_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 {
     /*
      * iomap based filesystems support direct I/O without need for
      * this callback. However, it still needs to be set in
      * inode->a_ops so that open/fcntl know that direct I/O is
      * generally supported.
      */
     return -EINVAL;
 }
 EXPORT_SYMBOL_GPL(noop_direct_IO);
 
 /* Because kfree isn't assignment-compatible with void(void*) ;-/ */
 void kfree_link(void *p)
 {
     kfree(p);
 }
 EXPORT_SYMBOL(kfree_link);
 
 struct inode *alloc_anon_inode(struct super_block *s)
 {
     static const struct address_space_operations anon_aops = {
         .dirty_folio    = noop_dirty_folio,
     };
     struct inode *inode = new_inode_pseudo(s);
 
     if (!inode)
         return ERR_PTR(-ENOMEM);
 
     inode->i_ino = get_next_ino();
     inode->i_mapping->a_ops = &anon_aops;
 
     /*
      * Mark the inode dirty from the very beginning,
      * that way it will never be moved to the dirty
      * list because mark_inode_dirty() will think
      * that it already _is_ on the dirty list.
      */
     inode->i_state = I_DIRTY;
     inode->i_mode = S_IRUSR | S_IWUSR;
     inode->i_uid = current_fsuid();
     inode->i_gid = current_fsgid();
     inode->i_flags |= S_PRIVATE;
     inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
     return inode;
 }
 EXPORT_SYMBOL(alloc_anon_inode);
 
 /**
  * simple_nosetlease - generic helper for prohibiting leases
  * @filp: file pointer
  * @arg: type of lease to obtain
  * @flp: new lease supplied for insertion
  * @priv: private data for lm_setup operation
  *
  * Generic helper for filesystems that do not wish to allow leases to be set.
  * All arguments are ignored and it just returns -EINVAL.
  */
 int
 simple_nosetlease(struct file *filp, long arg, struct file_lock **flp,
           void **priv)
 {
     return -EINVAL;
 }
 EXPORT_SYMBOL(simple_nosetlease);
 
 /**
  * simple_get_link - generic helper to get the target of "fast" symlinks
  * @dentry: not used here
  * @inode: the symlink inode
  * @done: not used here
  *
  * Generic helper for filesystems to use for symlink inodes where a pointer to
  * the symlink target is stored in ->i_link.  NOTE: this isn't normally called,
  * since as an optimization the path lookup code uses any non-NULL ->i_link
  * directly, without calling ->get_link().  But ->get_link() still must be set,
  * to mark the inode_operations as being for a symlink.
  *
  * Return: the symlink target
  */
 const char *simple_get_link(struct dentry *dentry, struct inode *inode,
                 struct delayed_call *done)
 {
     return inode->i_link;
 }
 EXPORT_SYMBOL(simple_get_link);
 
 const struct inode_operations simple_symlink_inode_operations = {
     .get_link = simple_get_link,
 };
 EXPORT_SYMBOL(simple_symlink_inode_operations);
 
 /*
  * Operations for a permanently empty directory.
  */
 static struct dentry *empty_dir_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 {
     return ERR_PTR(-ENOENT);
 }
 
 static int empty_dir_getattr(struct user_namespace *mnt_userns,
                  const struct path *path, struct kstat *stat,
                  u32 request_mask, unsigned int query_flags)
 {
     struct inode *inode = d_inode(path->dentry);
     generic_fillattr(&init_user_ns, inode, stat);
     return 0;
 }
 
 static int empty_dir_setattr(struct user_namespace *mnt_userns,
                  struct dentry *dentry, struct iattr *attr)
 {
     return -EPERM;
 }
 
 static ssize_t empty_dir_listxattr(struct dentry *dentry, char *list, size_t size)
 {
     return -EOPNOTSUPP;
 }
 
 static const struct inode_operations empty_dir_inode_operations = {
     .lookup     = empty_dir_lookup,
     .permission = generic_permission,
     .setattr    = empty_dir_setattr,
     .getattr    = empty_dir_getattr,
     .listxattr  = empty_dir_listxattr,
 };
 
 static loff_t empty_dir_llseek(struct file *file, loff_t offset, int whence)
 {
     /* An empty directory has two entries . and .. at offsets 0 and 1 */
     return generic_file_llseek_size(file, offset, whence, 2, 2);
 }
 
 static int empty_dir_readdir(struct file *file, struct dir_context *ctx)
 {
     dir_emit_dots(file, ctx);
     return 0;
 }
 
 static const struct file_operations empty_dir_operations = {
     .llseek     = empty_dir_llseek,
     .read       = generic_read_dir,
     .iterate_shared = empty_dir_readdir,
     .fsync      = noop_fsync,
 };
 
 
 void make_empty_dir_inode(struct inode *inode)
 {
     set_nlink(inode, 2);
     inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO;
     inode->i_uid = GLOBAL_ROOT_UID;
     inode->i_gid = GLOBAL_ROOT_GID;
     inode->i_rdev = 0;
     inode->i_size = 0;
     inode->i_blkbits = PAGE_SHIFT;
     inode->i_blocks = 0;
 
     inode->i_op = &empty_dir_inode_operations;
     inode->i_opflags &= ~IOP_XATTR;
     inode->i_fop = &empty_dir_operations;
 }
 
 bool is_empty_dir_inode(struct inode *inode)
 {
     return (inode->i_fop == &empty_dir_operations) &&
         (inode->i_op == &empty_dir_inode_operations);
 }
 
 #if IS_ENABLED(CONFIG_UNICODE)
 /*
  * Determine if the name of a dentry should be casefolded.
  *
  * Return: if names will need casefolding
  */
 static bool needs_casefold(const struct inode *dir)
 {
     return IS_CASEFOLDED(dir) && dir->i_sb->s_encoding;
 }
 
 /**
  * generic_ci_d_compare - generic d_compare implementation for casefolding filesystems
  * @dentry: dentry whose name we are checking against
  * @len:    len of name of dentry
  * @str:    str pointer to name of dentry
  * @name:   Name to compare against
  *
  * Return: 0 if names match, 1 if mismatch, or -ERRNO
  */
 static int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
                 const char *str, const struct qstr *name)
 {
     const struct dentry *parent = READ_ONCE(dentry->d_parent);
     const struct inode *dir = READ_ONCE(parent->d_inode);
     const struct super_block *sb = dentry->d_sb;
     const struct unicode_map *um = sb->s_encoding;
     struct qstr qstr = QSTR_INIT(str, len);
     char strbuf[DNAME_INLINE_LEN];
     int ret;
 
     if (!dir || !needs_casefold(dir))
         goto fallback;
     /*
      * If the dentry name is stored in-line, then it may be concurrently
      * modified by a rename.  If this happens, the VFS will eventually retry
      * the lookup, so it doesn't matter what ->d_compare() returns.
      * However, it's unsafe to call utf8_strncasecmp() with an unstable
      * string.  Therefore, we have to copy the name into a temporary buffer.
      */
     if (len <= DNAME_INLINE_LEN - 1) {
         memcpy(strbuf, str, len);
         strbuf[len] = 0;
         qstr.name = strbuf;
         /* prevent compiler from optimizing out the temporary buffer */
         barrier();
     }
     ret = utf8_strncasecmp(um, name, &qstr);
     if (ret >= 0)
         return ret;
 
     if (sb_has_strict_encoding(sb))
         return -EINVAL;
 fallback:
     if (len != name->len)
         return 1;
     return !!memcmp(str, name->name, len);
 }
 
 /**
  * generic_ci_d_hash - generic d_hash implementation for casefolding filesystems
  * @dentry: dentry of the parent directory
  * @str:    qstr of name whose hash we should fill in
  *
  * Return: 0 if hash was successful or unchanged, and -EINVAL on error
  */
 static int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str)
 {
     const struct inode *dir = READ_ONCE(dentry->d_inode);
     struct super_block *sb = dentry->d_sb;
     const struct unicode_map *um = sb->s_encoding;
     int ret = 0;
 
     if (!dir || !needs_casefold(dir))
         return 0;
 
     ret = utf8_casefold_hash(um, dentry, str);
     if (ret < 0 && sb_has_strict_encoding(sb))
         return -EINVAL;
     return 0;
 }
 
 static const struct dentry_operations generic_ci_dentry_ops = {
     .d_hash = generic_ci_d_hash,
     .d_compare = generic_ci_d_compare,
 };
 #endif
 
 #ifdef CONFIG_FS_ENCRYPTION
 static const struct dentry_operations generic_encrypted_dentry_ops = {
     .d_revalidate = fscrypt_d_revalidate,
 };
 #endif
 
 #if defined(CONFIG_FS_ENCRYPTION) && IS_ENABLED(CONFIG_UNICODE)
 static const struct dentry_operations generic_encrypted_ci_dentry_ops = {
     .d_hash = generic_ci_d_hash,
     .d_compare = generic_ci_d_compare,
     .d_revalidate = fscrypt_d_revalidate,
 };
 #endif
 
 /**
  * generic_set_encrypted_ci_d_ops - helper for setting d_ops for given dentry
  * @dentry: dentry to set ops on
  *
  * Casefolded directories need d_hash and d_compare set, so that the dentries
  * contained in them are handled case-insensitively.  Note that these operations
  * are needed on the parent directory rather than on the dentries in it, and
  * while the casefolding flag can be toggled on and off on an empty directory,
  * dentry_operations can't be changed later.  As a result, if the filesystem has
  * casefolding support enabled at all, we have to give all dentries the
  * casefolding operations even if their inode doesn't have the casefolding flag
  * currently (and thus the casefolding ops would be no-ops for now).
  *
  * Encryption works differently in that the only dentry operation it needs is
  * d_revalidate, which it only needs on dentries that have the no-key name flag.
  * The no-key flag can't be set "later", so we don't have to worry about that.
  *
  * Finally, to maximize compatibility with overlayfs (which isn't compatible
  * with certain dentry operations) and to avoid taking an unnecessary
  * performance hit, we use custom dentry_operations for each possible
  * combination rather than always installing all operations.
  */
 void generic_set_encrypted_ci_d_ops(struct dentry *dentry)
 {
 #ifdef CONFIG_FS_ENCRYPTION
     bool needs_encrypt_ops = dentry->d_flags & DCACHE_NOKEY_NAME;
 #endif
 #if IS_ENABLED(CONFIG_UNICODE)
     bool needs_ci_ops = dentry->d_sb->s_encoding;
 #endif
 #if defined(CONFIG_FS_ENCRYPTION) && IS_ENABLED(CONFIG_UNICODE)
     if (needs_encrypt_ops && needs_ci_ops) {
         d_set_d_op(dentry, &generic_encrypted_ci_dentry_ops);
         return;
     }
 #endif
 #ifdef CONFIG_FS_ENCRYPTION
     if (needs_encrypt_ops) {
         d_set_d_op(dentry, &generic_encrypted_dentry_ops);
         return;
     }
 #endif
 #if IS_ENABLED(CONFIG_UNICODE)
     if (needs_ci_ops) {
         d_set_d_op(dentry, &generic_ci_dentry_ops);
         return;
     }
 #endif
 }
 EXPORT_SYMBOL(generic_set_encrypted_ci_d_ops);

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