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 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 1991, 1992 Linus Torvalds
  * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
  * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
  * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>
  * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au>
  *  -  July2000
  * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - may 2001
  */
 
 /*
  * This handles all read/write requests to block devices
  */
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/blk-pm.h>
 #include <linux/blk-integrity.h>
 #include <linux/highmem.h>
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/kernel_stat.h>
 #include <linux/string.h>
 #include <linux/init.h>
 #include <linux/completion.h>
 #include <linux/slab.h>
 #include <linux/swap.h>
 #include <linux/writeback.h>
 #include <linux/task_io_accounting_ops.h>
 #include <linux/fault-inject.h>
 #include <linux/list_sort.h>
 #include <linux/delay.h>
 #include <linux/ratelimit.h>
 #include <linux/pm_runtime.h>
 #include <linux/t10-pi.h>
 #include <linux/debugfs.h>
 #include <linux/bpf.h>
 #include <linux/psi.h>
 #include <linux/part_stat.h>
 #include <linux/sched/sysctl.h>
 #include <linux/blk-crypto.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/block.h>
 
 #include "blk.h"
 #include "blk-mq-sched.h"
 #include "blk-pm.h"
 #include "blk-cgroup.h"
 #include "blk-throttle.h"
 
 struct dentry *blk_debugfs_root;
 
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_split);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_unplug);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_insert);
 
 DEFINE_IDA(blk_queue_ida);
 
 /*
  * For queue allocation
  */
 struct kmem_cache *blk_requestq_cachep;
 struct kmem_cache *blk_requestq_srcu_cachep;
 
 /*
  * Controlling structure to kblockd
  */
 static struct workqueue_struct *kblockd_workqueue;
 
 /**
  * blk_queue_flag_set - atomically set a queue flag
  * @flag: flag to be set
  * @q: request queue
  */
 void blk_queue_flag_set(unsigned int flag, struct request_queue *q)
 {
     set_bit(flag, &q->queue_flags);
 }
 EXPORT_SYMBOL(blk_queue_flag_set);
 
 /**
  * blk_queue_flag_clear - atomically clear a queue flag
  * @flag: flag to be cleared
  * @q: request queue
  */
 void blk_queue_flag_clear(unsigned int flag, struct request_queue *q)
 {
     clear_bit(flag, &q->queue_flags);
 }
 EXPORT_SYMBOL(blk_queue_flag_clear);
 
 /**
  * blk_queue_flag_test_and_set - atomically test and set a queue flag
  * @flag: flag to be set
  * @q: request queue
  *
  * Returns the previous value of @flag - 0 if the flag was not set and 1 if
  * the flag was already set.
  */
 bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q)
 {
     return test_and_set_bit(flag, &q->queue_flags);
 }
 EXPORT_SYMBOL_GPL(blk_queue_flag_test_and_set);
 
 #define REQ_OP_NAME(name) [REQ_OP_##name] = #name
 static const char *const blk_op_name[] = {
     REQ_OP_NAME(READ),
     REQ_OP_NAME(WRITE),
     REQ_OP_NAME(FLUSH),
     REQ_OP_NAME(DISCARD),
     REQ_OP_NAME(SECURE_ERASE),
     REQ_OP_NAME(ZONE_RESET),
     REQ_OP_NAME(ZONE_RESET_ALL),
     REQ_OP_NAME(ZONE_OPEN),
     REQ_OP_NAME(ZONE_CLOSE),
     REQ_OP_NAME(ZONE_FINISH),
     REQ_OP_NAME(ZONE_APPEND),
     REQ_OP_NAME(WRITE_ZEROES),
     REQ_OP_NAME(DRV_IN),
     REQ_OP_NAME(DRV_OUT),
 };
 #undef REQ_OP_NAME
 
 /**
  * blk_op_str - Return string XXX in the REQ_OP_XXX.
  * @op: REQ_OP_XXX.
  *
  * Description: Centralize block layer function to convert REQ_OP_XXX into
  * string format. Useful in the debugging and tracing bio or request. For
  * invalid REQ_OP_XXX it returns string "UNKNOWN".
  */
 inline const char *blk_op_str(enum req_op op)
 {
     const char *op_str = "UNKNOWN";
 
     if (op < ARRAY_SIZE(blk_op_name) && blk_op_name[op])
         op_str = blk_op_name[op];
 
     return op_str;
 }
 EXPORT_SYMBOL_GPL(blk_op_str);
 
 static const struct {
     int     errno;
     const char  *name;
 } blk_errors[] = {
     [BLK_STS_OK]        = { 0,      "" },
     [BLK_STS_NOTSUPP]   = { -EOPNOTSUPP, "operation not supported" },
     [BLK_STS_TIMEOUT]   = { -ETIMEDOUT, "timeout" },
     [BLK_STS_NOSPC]     = { -ENOSPC,    "critical space allocation" },
     [BLK_STS_TRANSPORT] = { -ENOLINK,   "recoverable transport" },
     [BLK_STS_TARGET]    = { -EREMOTEIO, "critical target" },
     [BLK_STS_NEXUS]     = { -EBADE, "critical nexus" },
     [BLK_STS_MEDIUM]    = { -ENODATA,   "critical medium" },
     [BLK_STS_PROTECTION]    = { -EILSEQ,    "protection" },
     [BLK_STS_RESOURCE]  = { -ENOMEM,    "kernel resource" },
     [BLK_STS_DEV_RESOURCE]  = { -EBUSY, "device resource" },
     [BLK_STS_AGAIN]     = { -EAGAIN,    "nonblocking retry" },
     [BLK_STS_OFFLINE]   = { -ENODEV,    "device offline" },
 
     /* device mapper special case, should not leak out: */
     [BLK_STS_DM_REQUEUE]    = { -EREMCHG, "dm internal retry" },
 
     /* zone device specific errors */
     [BLK_STS_ZONE_OPEN_RESOURCE]    = { -ETOOMANYREFS, "open zones exceeded" },
     [BLK_STS_ZONE_ACTIVE_RESOURCE]  = { -EOVERFLOW, "active zones exceeded" },
 
     /* everything else not covered above: */
     [BLK_STS_IOERR]     = { -EIO,   "I/O" },
 };
 
 blk_status_t errno_to_blk_status(int errno)
 {
     int i;
 
     for (i = 0; i < ARRAY_SIZE(blk_errors); i++) {
         if (blk_errors[i].errno == errno)
             return (__force blk_status_t)i;
     }
 
     return BLK_STS_IOERR;
 }
 EXPORT_SYMBOL_GPL(errno_to_blk_status);
 
 int blk_status_to_errno(blk_status_t status)
 {
     int idx = (__force int)status;
 
     if (WARN_ON_ONCE(idx >= ARRAY_SIZE(blk_errors)))
         return -EIO;
     return blk_errors[idx].errno;
 }
 EXPORT_SYMBOL_GPL(blk_status_to_errno);
 
 const char *blk_status_to_str(blk_status_t status)
 {
     int idx = (__force int)status;
 
     if (WARN_ON_ONCE(idx >= ARRAY_SIZE(blk_errors)))
         return "<null>";
     return blk_errors[idx].name;
 }
 
 /**
  * blk_sync_queue - cancel any pending callbacks on a queue
  * @q: the queue
  *
  * Description:
  *     The block layer may perform asynchronous callback activity
  *     on a queue, such as calling the unplug function after a timeout.
  *     A block device may call blk_sync_queue to ensure that any
  *     such activity is cancelled, thus allowing it to release resources
  *     that the callbacks might use. The caller must already have made sure
  *     that its ->submit_bio will not re-add plugging prior to calling
  *     this function.
  *
  *     This function does not cancel any asynchronous activity arising
  *     out of elevator or throttling code. That would require elevator_exit()
  *     and blkcg_exit_queue() to be called with queue lock initialized.
  *
  */
 void blk_sync_queue(struct request_queue *q)
 {
     del_timer_sync(&q->timeout);
     cancel_work_sync(&q->timeout_work);
 }
 EXPORT_SYMBOL(blk_sync_queue);
 
 /**
  * blk_set_pm_only - increment pm_only counter
  * @q: request queue pointer
  */
 void blk_set_pm_only(struct request_queue *q)
 {
     atomic_inc(&q->pm_only);
 }
 EXPORT_SYMBOL_GPL(blk_set_pm_only);
 
 void blk_clear_pm_only(struct request_queue *q)
 {
     int pm_only;
 
     pm_only = atomic_dec_return(&q->pm_only);
     WARN_ON_ONCE(pm_only < 0);
     if (pm_only == 0)
         wake_up_all(&q->mq_freeze_wq);
 }
 EXPORT_SYMBOL_GPL(blk_clear_pm_only);
 
 /**
  * blk_put_queue - decrement the request_queue refcount
  * @q: the request_queue structure to decrement the refcount for
  *
  * Decrements the refcount of the request_queue kobject. When this reaches 0
  * we'll have blk_release_queue() called.
  *
  * Context: Any context, but the last reference must not be dropped from
  *          atomic context.
  */
 void blk_put_queue(struct request_queue *q)
 {
     kobject_put(&q->kobj);
 }
 EXPORT_SYMBOL(blk_put_queue);
 
 void blk_queue_start_drain(struct request_queue *q)
 {
     /*
      * When queue DYING flag is set, we need to block new req
      * entering queue, so we call blk_freeze_queue_start() to
      * prevent I/O from crossing blk_queue_enter().
      */
     blk_freeze_queue_start(q);
     if (queue_is_mq(q))
         blk_mq_wake_waiters(q);
     /* Make blk_queue_enter() reexamine the DYING flag. */
     wake_up_all(&q->mq_freeze_wq);
 }
 
 /**
  * blk_queue_enter() - try to increase q->q_usage_counter
  * @q: request queue pointer
  * @flags: BLK_MQ_REQ_NOWAIT and/or BLK_MQ_REQ_PM
  */
 int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
 {
     const bool pm = flags & BLK_MQ_REQ_PM;
 
     while (!blk_try_enter_queue(q, pm)) {
         if (flags & BLK_MQ_REQ_NOWAIT)
             return -EAGAIN;
 
         /*
          * read pair of barrier in blk_freeze_queue_start(), we need to
          * order reading __PERCPU_REF_DEAD flag of .q_usage_counter and
          * reading .mq_freeze_depth or queue dying flag, otherwise the
          * following wait may never return if the two reads are
          * reordered.
          */
         smp_rmb();
         wait_event(q->mq_freeze_wq,
                (!q->mq_freeze_depth &&
                 blk_pm_resume_queue(pm, q)) ||
                blk_queue_dying(q));
         if (blk_queue_dying(q))
             return -ENODEV;
     }
 
     return 0;
 }
 
 int __bio_queue_enter(struct request_queue *q, struct bio *bio)
 {
     while (!blk_try_enter_queue(q, false)) {
         struct gendisk *disk = bio->bi_bdev->bd_disk;
 
         if (bio->bi_opf & REQ_NOWAIT) {
             if (test_bit(GD_DEAD, &disk->state))
                 goto dead;
             bio_wouldblock_error(bio);
             return -EAGAIN;
         }
 
         /*
          * read pair of barrier in blk_freeze_queue_start(), we need to
          * order reading __PERCPU_REF_DEAD flag of .q_usage_counter and
          * reading .mq_freeze_depth or queue dying flag, otherwise the
          * following wait may never return if the two reads are
          * reordered.
          */
         smp_rmb();
         wait_event(q->mq_freeze_wq,
                (!q->mq_freeze_depth &&
                 blk_pm_resume_queue(false, q)) ||
                test_bit(GD_DEAD, &disk->state));
         if (test_bit(GD_DEAD, &disk->state))
             goto dead;
     }
 
     return 0;
 dead:
     bio_io_error(bio);
     return -ENODEV;
 }
 
 void blk_queue_exit(struct request_queue *q)
 {
     percpu_ref_put(&q->q_usage_counter);
 }
 
 static void blk_queue_usage_counter_release(struct percpu_ref *ref)
 {
     struct request_queue *q =
         container_of(ref, struct request_queue, q_usage_counter);
 
     wake_up_all(&q->mq_freeze_wq);
 }
 
 static void blk_rq_timed_out_timer(struct timer_list *t)
 {
     struct request_queue *q = from_timer(q, t, timeout);
 
     kblockd_schedule_work(&q->timeout_work);
 }
 
 static void blk_timeout_work(struct work_struct *work)
 {
 }
 
 struct request_queue *blk_alloc_queue(int node_id, bool alloc_srcu)
 {
     struct request_queue *q;
 
     q = kmem_cache_alloc_node(blk_get_queue_kmem_cache(alloc_srcu),
             GFP_KERNEL | __GFP_ZERO, node_id);
     if (!q)
         return NULL;
 
     if (alloc_srcu) {
         blk_queue_flag_set(QUEUE_FLAG_HAS_SRCU, q);
         if (init_srcu_struct(q->srcu) != 0)
             goto fail_q;
     }
 
     q->last_merge = NULL;
 
     q->id = ida_alloc(&blk_queue_ida, GFP_KERNEL);
     if (q->id < 0)
         goto fail_srcu;
 
     q->stats = blk_alloc_queue_stats();
     if (!q->stats)
         goto fail_id;
 
     q->node = node_id;
 
     atomic_set(&q->nr_active_requests_shared_tags, 0);
 
     timer_setup(&q->timeout, blk_rq_timed_out_timer, 0);
     INIT_WORK(&q->timeout_work, blk_timeout_work);
     INIT_LIST_HEAD(&q->icq_list);
 
     kobject_init(&q->kobj, &blk_queue_ktype);
 
     mutex_init(&q->debugfs_mutex);
     mutex_init(&q->sysfs_lock);
     mutex_init(&q->sysfs_dir_lock);
     spin_lock_init(&q->queue_lock);
 
     init_waitqueue_head(&q->mq_freeze_wq);
     mutex_init(&q->mq_freeze_lock);
 
     /*
      * Init percpu_ref in atomic mode so that it's faster to shutdown.
      * See blk_register_queue() for details.
      */
     if (percpu_ref_init(&q->q_usage_counter,
                 blk_queue_usage_counter_release,
                 PERCPU_REF_INIT_ATOMIC, GFP_KERNEL))
         goto fail_stats;
 
     blk_queue_dma_alignment(q, 511);
     blk_set_default_limits(&q->limits);
     q->nr_requests = BLKDEV_DEFAULT_RQ;
 
     return q;
 
 fail_stats:
     blk_free_queue_stats(q->stats);
 fail_id:
     ida_free(&blk_queue_ida, q->id);
 fail_srcu:
     if (alloc_srcu)
         cleanup_srcu_struct(q->srcu);
 fail_q:
     kmem_cache_free(blk_get_queue_kmem_cache(alloc_srcu), q);
     return NULL;
 }
 
 /**
  * blk_get_queue - increment the request_queue refcount
  * @q: the request_queue structure to increment the refcount for
  *
  * Increment the refcount of the request_queue kobject.
  *
  * Context: Any context.
  */
 bool blk_get_queue(struct request_queue *q)
 {
     if (unlikely(blk_queue_dying(q)))
         return false;
     kobject_get(&q->kobj);
     return true;
 }
 EXPORT_SYMBOL(blk_get_queue);
 
 #ifdef CONFIG_FAIL_MAKE_REQUEST
 
 static DECLARE_FAULT_ATTR(fail_make_request);
 
 static int __init setup_fail_make_request(char *str)
 {
     return setup_fault_attr(&fail_make_request, str);
 }
 __setup("fail_make_request=", setup_fail_make_request);
 
 bool should_fail_request(struct block_device *part, unsigned int bytes)
 {
     return part->bd_make_it_fail && should_fail(&fail_make_request, bytes);
 }
 
 static int __init fail_make_request_debugfs(void)
 {
     struct dentry *dir = fault_create_debugfs_attr("fail_make_request",
                         NULL, &fail_make_request);
 
     return PTR_ERR_OR_ZERO(dir);
 }
 
 late_initcall(fail_make_request_debugfs);
 #endif /* CONFIG_FAIL_MAKE_REQUEST */
 
 static inline bool bio_check_ro(struct bio *bio)
 {
     if (op_is_write(bio_op(bio)) && bdev_read_only(bio->bi_bdev)) {
         if (op_is_flush(bio->bi_opf) && !bio_sectors(bio))
             return false;
         pr_warn("Trying to write to read-only block-device %pg\n",
             bio->bi_bdev);
         /* Older lvm-tools actually trigger this */
         return false;
     }
 
     return false;
 }
 
 static noinline int should_fail_bio(struct bio *bio)
 {
     if (should_fail_request(bdev_whole(bio->bi_bdev), bio->bi_iter.bi_size))
         return -EIO;
     return 0;
 }
 ALLOW_ERROR_INJECTION(should_fail_bio, ERRNO);
 
 /*
  * Check whether this bio extends beyond the end of the device or partition.
  * This may well happen - the kernel calls bread() without checking the size of
  * the device, e.g., when mounting a file system.
  */
 static inline int bio_check_eod(struct bio *bio)
 {
     sector_t maxsector = bdev_nr_sectors(bio->bi_bdev);
     unsigned int nr_sectors = bio_sectors(bio);
 
     if (nr_sectors && maxsector &&
         (nr_sectors > maxsector ||
          bio->bi_iter.bi_sector > maxsector - nr_sectors)) {
         pr_info_ratelimited("%s: attempt to access beyond end of device\n"
                     "%pg: rw=%d, sector=%llu, nr_sectors = %u limit=%llu\n",
                     current->comm, bio->bi_bdev, bio->bi_opf,
                     bio->bi_iter.bi_sector, nr_sectors, maxsector);
         return -EIO;
     }
     return 0;
 }
 
 /*
  * Remap block n of partition p to block n+start(p) of the disk.
  */
 static int blk_partition_remap(struct bio *bio)
 {
     struct block_device *p = bio->bi_bdev;
 
     if (unlikely(should_fail_request(p, bio->bi_iter.bi_size)))
         return -EIO;
     if (bio_sectors(bio)) {
         bio->bi_iter.bi_sector += p->bd_start_sect;
         trace_block_bio_remap(bio, p->bd_dev,
                       bio->bi_iter.bi_sector -
                       p->bd_start_sect);
     }
     bio_set_flag(bio, BIO_REMAPPED);
     return 0;
 }
 
 /*
  * Check write append to a zoned block device.
  */
 static inline blk_status_t blk_check_zone_append(struct request_queue *q,
                          struct bio *bio)
 {
     int nr_sectors = bio_sectors(bio);
 
     /* Only applicable to zoned block devices */
     if (!bdev_is_zoned(bio->bi_bdev))
         return BLK_STS_NOTSUPP;
 
     /* The bio sector must point to the start of a sequential zone */
     if (bio->bi_iter.bi_sector & (bdev_zone_sectors(bio->bi_bdev) - 1) ||
         !bio_zone_is_seq(bio))
         return BLK_STS_IOERR;
 
     /*
      * Not allowed to cross zone boundaries. Otherwise, the BIO will be
      * split and could result in non-contiguous sectors being written in
      * different zones.
      */
     if (nr_sectors > q->limits.chunk_sectors)
         return BLK_STS_IOERR;
 
     /* Make sure the BIO is small enough and will not get split */
     if (nr_sectors > q->limits.max_zone_append_sectors)
         return BLK_STS_IOERR;
 
     bio->bi_opf |= REQ_NOMERGE;
 
     return BLK_STS_OK;
 }
 
 static void __submit_bio(struct bio *bio)
 {
     struct gendisk *disk = bio->bi_bdev->bd_disk;
 
     if (unlikely(!blk_crypto_bio_prep(&bio)))
         return;
 
     if (!disk->fops->submit_bio) {
         blk_mq_submit_bio(bio);
     } else if (likely(bio_queue_enter(bio) == 0)) {
         disk->fops->submit_bio(bio);
         blk_queue_exit(disk->queue);
     }
 }
 
 /*
  * The loop in this function may be a bit non-obvious, and so deserves some
  * explanation:
  *
  *  - Before entering the loop, bio->bi_next is NULL (as all callers ensure
  *    that), so we have a list with a single bio.
  *  - We pretend that we have just taken it off a longer list, so we assign
  *    bio_list to a pointer to the bio_list_on_stack, thus initialising the
  *    bio_list of new bios to be added.  ->submit_bio() may indeed add some more
  *    bios through a recursive call to submit_bio_noacct.  If it did, we find a
  *    non-NULL value in bio_list and re-enter the loop from the top.
  *  - In this case we really did just take the bio of the top of the list (no
  *    pretending) and so remove it from bio_list, and call into ->submit_bio()
  *    again.
  *
  * bio_list_on_stack[0] contains bios submitted by the current ->submit_bio.
  * bio_list_on_stack[1] contains bios that were submitted before the current
  *  ->submit_bio, but that haven't been processed yet.
  */
 static void __submit_bio_noacct(struct bio *bio)
 {
     struct bio_list bio_list_on_stack[2];
 
     BUG_ON(bio->bi_next);
 
     bio_list_init(&bio_list_on_stack[0]);
     current->bio_list = bio_list_on_stack;
 
     do {
         struct request_queue *q = bdev_get_queue(bio->bi_bdev);
         struct bio_list lower, same;
 
         /*
          * Create a fresh bio_list for all subordinate requests.
          */
         bio_list_on_stack[1] = bio_list_on_stack[0];
         bio_list_init(&bio_list_on_stack[0]);
 
         __submit_bio(bio);
 
         /*
          * Sort new bios into those for a lower level and those for the
          * same level.
          */
         bio_list_init(&lower);
         bio_list_init(&same);
         while ((bio = bio_list_pop(&bio_list_on_stack[0])) != NULL)
             if (q == bdev_get_queue(bio->bi_bdev))
                 bio_list_add(&same, bio);
             else
                 bio_list_add(&lower, bio);
 
         /*
          * Now assemble so we handle the lowest level first.
          */
         bio_list_merge(&bio_list_on_stack[0], &lower);
         bio_list_merge(&bio_list_on_stack[0], &same);
         bio_list_merge(&bio_list_on_stack[0], &bio_list_on_stack[1]);
     } while ((bio = bio_list_pop(&bio_list_on_stack[0])));
 
     current->bio_list = NULL;
 }
 
 static void __submit_bio_noacct_mq(struct bio *bio)
 {
     struct bio_list bio_list[2] = { };
 
     current->bio_list = bio_list;
 
     do {
         __submit_bio(bio);
     } while ((bio = bio_list_pop(&bio_list[0])));
 
     current->bio_list = NULL;
 }
 
 void submit_bio_noacct_nocheck(struct bio *bio)
 {
     /*
      * We only want one ->submit_bio to be active at a time, else stack
      * usage with stacked devices could be a problem.  Use current->bio_list
      * to collect a list of requests submited by a ->submit_bio method while
      * it is active, and then process them after it returned.
      */
     if (current->bio_list)
         bio_list_add(&current->bio_list[0], bio);
     else if (!bio->bi_bdev->bd_disk->fops->submit_bio)
         __submit_bio_noacct_mq(bio);
     else
         __submit_bio_noacct(bio);
 }
 
 /**
  * submit_bio_noacct - re-submit a bio to the block device layer for I/O
  * @bio:  The bio describing the location in memory and on the device.
  *
  * This is a version of submit_bio() that shall only be used for I/O that is
  * resubmitted to lower level drivers by stacking block drivers.  All file
  * systems and other upper level users of the block layer should use
  * submit_bio() instead.
  */
 void submit_bio_noacct(struct bio *bio)
 {
     struct block_device *bdev = bio->bi_bdev;
     struct request_queue *q = bdev_get_queue(bdev);
     blk_status_t status = BLK_STS_IOERR;
     struct blk_plug *plug;
 
     might_sleep();
 
     plug = blk_mq_plug(bio);
     if (plug && plug->nowait)
         bio->bi_opf |= REQ_NOWAIT;
 
     /*
      * For a REQ_NOWAIT based request, return -EOPNOTSUPP
      * if queue does not support NOWAIT.
      */
     if ((bio->bi_opf & REQ_NOWAIT) && !blk_queue_nowait(q))
         goto not_supported;
 
     if (should_fail_bio(bio))
         goto end_io;
     if (unlikely(bio_check_ro(bio)))
         goto end_io;
     if (!bio_flagged(bio, BIO_REMAPPED)) {
         if (unlikely(bio_check_eod(bio)))
             goto end_io;
         if (bdev->bd_partno && unlikely(blk_partition_remap(bio)))
             goto end_io;
     }
 
     /*
      * Filter flush bio's early so that bio based drivers without flush
      * support don't have to worry about them.
      */
     if (op_is_flush(bio->bi_opf) &&
         !test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
         bio->bi_opf &= ~(REQ_PREFLUSH | REQ_FUA);
         if (!bio_sectors(bio)) {
             status = BLK_STS_OK;
             goto end_io;
         }
     }
 
     if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
         bio_clear_polled(bio);
 
     switch (bio_op(bio)) {
     case REQ_OP_DISCARD:
         if (!bdev_max_discard_sectors(bdev))
             goto not_supported;
         break;
     case REQ_OP_SECURE_ERASE:
         if (!bdev_max_secure_erase_sectors(bdev))
             goto not_supported;
         break;
     case REQ_OP_ZONE_APPEND:
         status = blk_check_zone_append(q, bio);
         if (status != BLK_STS_OK)
             goto end_io;
         break;
     case REQ_OP_ZONE_RESET:
     case REQ_OP_ZONE_OPEN:
     case REQ_OP_ZONE_CLOSE:
     case REQ_OP_ZONE_FINISH:
         if (!bdev_is_zoned(bio->bi_bdev))
             goto not_supported;
         break;
     case REQ_OP_ZONE_RESET_ALL:
         if (!bdev_is_zoned(bio->bi_bdev) || !blk_queue_zone_resetall(q))
             goto not_supported;
         break;
     case REQ_OP_WRITE_ZEROES:
         if (!q->limits.max_write_zeroes_sectors)
             goto not_supported;
         break;
     default:
         break;
     }
 
     if (blk_throtl_bio(bio))
         return;
 
     blk_cgroup_bio_start(bio);
     blkcg_bio_issue_init(bio);
 
     if (!bio_flagged(bio, BIO_TRACE_COMPLETION)) {
         trace_block_bio_queue(bio);
         /* Now that enqueuing has been traced, we need to trace
          * completion as well.
          */
         bio_set_flag(bio, BIO_TRACE_COMPLETION);
     }
     submit_bio_noacct_nocheck(bio);
     return;
 
 not_supported:
     status = BLK_STS_NOTSUPP;
 end_io:
     bio->bi_status = status;
     bio_endio(bio);
 }
 EXPORT_SYMBOL(submit_bio_noacct);
 
 /**
  * submit_bio - submit a bio to the block device layer for I/O
  * @bio: The &struct bio which describes the I/O
  *
  * submit_bio() is used to submit I/O requests to block devices.  It is passed a
  * fully set up &struct bio that describes the I/O that needs to be done.  The
  * bio will be send to the device described by the bi_bdev field.
  *
  * The success/failure status of the request, along with notification of
  * completion, is delivered asynchronously through the ->bi_end_io() callback
  * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
  * been called.
  */
 void submit_bio(struct bio *bio)
 {
     if (blkcg_punt_bio_submit(bio))
         return;
 
     if (bio_op(bio) == REQ_OP_READ) {
         task_io_account_read(bio->bi_iter.bi_size);
         count_vm_events(PGPGIN, bio_sectors(bio));
     } else if (bio_op(bio) == REQ_OP_WRITE) {
         count_vm_events(PGPGOUT, bio_sectors(bio));
     }
 
     /*
      * If we're reading data that is part of the userspace workingset, count
      * submission time as memory stall.  When the device is congested, or
      * the submitting cgroup IO-throttled, submission can be a significant
      * part of overall IO time.
      */
     if (unlikely(bio_op(bio) == REQ_OP_READ &&
         bio_flagged(bio, BIO_WORKINGSET))) {
         unsigned long pflags;
 
         psi_memstall_enter(&pflags);
         submit_bio_noacct(bio);
         psi_memstall_leave(&pflags);
         return;
     }
 
     submit_bio_noacct(bio);
 }
 EXPORT_SYMBOL(submit_bio);
 
 /**
  * bio_poll - poll for BIO completions
  * @bio: bio to poll for
  * @iob: batches of IO
  * @flags: BLK_POLL_* flags that control the behavior
  *
  * Poll for completions on queue associated with the bio. Returns number of
  * completed entries found.
  *
  * Note: the caller must either be the context that submitted @bio, or
  * be in a RCU critical section to prevent freeing of @bio.
  */
 int bio_poll(struct bio *bio, struct io_comp_batch *iob, unsigned int flags)
 {
     struct request_queue *q = bdev_get_queue(bio->bi_bdev);
     blk_qc_t cookie = READ_ONCE(bio->bi_cookie);
     int ret = 0;
 
     if (cookie == BLK_QC_T_NONE ||
         !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
         return 0;
 
     blk_flush_plug(current->plug, false);
 
     if (bio_queue_enter(bio))
         return 0;
     if (queue_is_mq(q)) {
         ret = blk_mq_poll(q, cookie, iob, flags);
     } else {
         struct gendisk *disk = q->disk;
 
         if (disk && disk->fops->poll_bio)
             ret = disk->fops->poll_bio(bio, iob, flags);
     }
     blk_queue_exit(q);
     return ret;
 }
 EXPORT_SYMBOL_GPL(bio_poll);
 
 /*
  * Helper to implement file_operations.iopoll.  Requires the bio to be stored
  * in iocb->private, and cleared before freeing the bio.
  */
 int iocb_bio_iopoll(struct kiocb *kiocb, struct io_comp_batch *iob,
             unsigned int flags)
 {
     struct bio *bio;
     int ret = 0;
 
     /*
      * Note: the bio cache only uses SLAB_TYPESAFE_BY_RCU, so bio can
      * point to a freshly allocated bio at this point.  If that happens
      * we have a few cases to consider:
      *
      *  1) the bio is beeing initialized and bi_bdev is NULL.  We can just
      *     simply nothing in this case
      *  2) the bio points to a not poll enabled device.  bio_poll will catch
      *     this and return 0
      *  3) the bio points to a poll capable device, including but not
      *     limited to the one that the original bio pointed to.  In this
      *     case we will call into the actual poll method and poll for I/O,
      *     even if we don't need to, but it won't cause harm either.
      *
      * For cases 2) and 3) above the RCU grace period ensures that bi_bdev
      * is still allocated. Because partitions hold a reference to the whole
      * device bdev and thus disk, the disk is also still valid.  Grabbing
      * a reference to the queue in bio_poll() ensures the hctxs and requests
      * are still valid as well.
      */
     rcu_read_lock();
     bio = READ_ONCE(kiocb->private);
     if (bio && bio->bi_bdev)
         ret = bio_poll(bio, iob, flags);
     rcu_read_unlock();
 
     return ret;
 }
 EXPORT_SYMBOL_GPL(iocb_bio_iopoll);
 
 void update_io_ticks(struct block_device *part, unsigned long now, bool end)
 {
     unsigned long stamp;
 again:
     stamp = READ_ONCE(part->bd_stamp);
     if (unlikely(time_after(now, stamp))) {
         if (likely(try_cmpxchg(&part->bd_stamp, &stamp, now)))
             __part_stat_add(part, io_ticks, end ? now - stamp : 1);
     }
     if (part->bd_partno) {
         part = bdev_whole(part);
         goto again;
     }
 }
 
 unsigned long bdev_start_io_acct(struct block_device *bdev,
                  unsigned int sectors, enum req_op op,
                  unsigned long start_time)
 {
     const int sgrp = op_stat_group(op);
 
     part_stat_lock();
     update_io_ticks(bdev, start_time, false);
     part_stat_inc(bdev, ios[sgrp]);
     part_stat_add(bdev, sectors[sgrp], sectors);
     part_stat_local_inc(bdev, in_flight[op_is_write(op)]);
     part_stat_unlock();
 
     return start_time;
 }
 EXPORT_SYMBOL(bdev_start_io_acct);
 
 /**
  * bio_start_io_acct_time - start I/O accounting for bio based drivers
  * @bio:    bio to start account for
  * @start_time: start time that should be passed back to bio_end_io_acct().
  */
 void bio_start_io_acct_time(struct bio *bio, unsigned long start_time)
 {
     bdev_start_io_acct(bio->bi_bdev, bio_sectors(bio),
                bio_op(bio), start_time);
 }
 EXPORT_SYMBOL_GPL(bio_start_io_acct_time);
 
 /**
  * bio_start_io_acct - start I/O accounting for bio based drivers
  * @bio:    bio to start account for
  *
  * Returns the start time that should be passed back to bio_end_io_acct().
  */
 unsigned long bio_start_io_acct(struct bio *bio)
 {
     return bdev_start_io_acct(bio->bi_bdev, bio_sectors(bio),
                   bio_op(bio), jiffies);
 }
 EXPORT_SYMBOL_GPL(bio_start_io_acct);
 
 void bdev_end_io_acct(struct block_device *bdev, enum req_op op,
               unsigned long start_time)
 {
     const int sgrp = op_stat_group(op);
     unsigned long now = READ_ONCE(jiffies);
     unsigned long duration = now - start_time;
 
     part_stat_lock();
     update_io_ticks(bdev, now, true);
     part_stat_add(bdev, nsecs[sgrp], jiffies_to_nsecs(duration));
     part_stat_local_dec(bdev, in_flight[op_is_write(op)]);
     part_stat_unlock();
 }
 EXPORT_SYMBOL(bdev_end_io_acct);
 
 void bio_end_io_acct_remapped(struct bio *bio, unsigned long start_time,
                   struct block_device *orig_bdev)
 {
     bdev_end_io_acct(orig_bdev, bio_op(bio), start_time);
 }
 EXPORT_SYMBOL_GPL(bio_end_io_acct_remapped);
 
 /**
  * blk_lld_busy - Check if underlying low-level drivers of a device are busy
  * @q : the queue of the device being checked
  *
  * Description:
  *    Check if underlying low-level drivers of a device are busy.
  *    If the drivers want to export their busy state, they must set own
  *    exporting function using blk_queue_lld_busy() first.
  *
  *    Basically, this function is used only by request stacking drivers
  *    to stop dispatching requests to underlying devices when underlying
  *    devices are busy.  This behavior helps more I/O merging on the queue
  *    of the request stacking driver and prevents I/O throughput regression
  *    on burst I/O load.
  *
  * Return:
  *    0 - Not busy (The request stacking driver should dispatch request)
  *    1 - Busy (The request stacking driver should stop dispatching request)
  */
 int blk_lld_busy(struct request_queue *q)
 {
     if (queue_is_mq(q) && q->mq_ops->busy)
         return q->mq_ops->busy(q);
 
     return 0;
 }
 EXPORT_SYMBOL_GPL(blk_lld_busy);
 
 int kblockd_schedule_work(struct work_struct *work)
 {
     return queue_work(kblockd_workqueue, work);
 }
 EXPORT_SYMBOL(kblockd_schedule_work);
 
 int kblockd_mod_delayed_work_on(int cpu, struct delayed_work *dwork,
                 unsigned long delay)
 {
     return mod_delayed_work_on(cpu, kblockd_workqueue, dwork, delay);
 }
 EXPORT_SYMBOL(kblockd_mod_delayed_work_on);
 
 void blk_start_plug_nr_ios(struct blk_plug *plug, unsigned short nr_ios)
 {
     struct task_struct *tsk = current;
 
     /*
      * If this is a nested plug, don't actually assign it.
      */
     if (tsk->plug)
         return;
 
     plug->mq_list = NULL;
     plug->cached_rq = NULL;
     plug->nr_ios = min_t(unsigned short, nr_ios, BLK_MAX_REQUEST_COUNT);
     plug->rq_count = 0;
     plug->multiple_queues = false;
     plug->has_elevator = false;
     plug->nowait = false;
     INIT_LIST_HEAD(&plug->cb_list);
 
     /*
      * Store ordering should not be needed here, since a potential
      * preempt will imply a full memory barrier
      */
     tsk->plug = plug;
 }
 
 /**
  * blk_start_plug - initialize blk_plug and track it inside the task_struct
  * @plug:   The &struct blk_plug that needs to be initialized
  *
  * Description:
  *   blk_start_plug() indicates to the block layer an intent by the caller
  *   to submit multiple I/O requests in a batch.  The block layer may use
  *   this hint to defer submitting I/Os from the caller until blk_finish_plug()
  *   is called.  However, the block layer may choose to submit requests
  *   before a call to blk_finish_plug() if the number of queued I/Os
  *   exceeds %BLK_MAX_REQUEST_COUNT, or if the size of the I/O is larger than
  *   %BLK_PLUG_FLUSH_SIZE.  The queued I/Os may also be submitted early if
  *   the task schedules (see below).
  *
  *   Tracking blk_plug inside the task_struct will help with auto-flushing the
  *   pending I/O should the task end up blocking between blk_start_plug() and
  *   blk_finish_plug(). This is important from a performance perspective, but
  *   also ensures that we don't deadlock. For instance, if the task is blocking
  *   for a memory allocation, memory reclaim could end up wanting to free a
  *   page belonging to that request that is currently residing in our private
  *   plug. By flushing the pending I/O when the process goes to sleep, we avoid
  *   this kind of deadlock.
  */
 void blk_start_plug(struct blk_plug *plug)
 {
     blk_start_plug_nr_ios(plug, 1);
 }
 EXPORT_SYMBOL(blk_start_plug);
 
 static void flush_plug_callbacks(struct blk_plug *plug, bool from_schedule)
 {
     LIST_HEAD(callbacks);
 
     while (!list_empty(&plug->cb_list)) {
         list_splice_init(&plug->cb_list, &callbacks);
 
         while (!list_empty(&callbacks)) {
             struct blk_plug_cb *cb = list_first_entry(&callbacks,
                               struct blk_plug_cb,
                               list);
             list_del(&cb->list);
             cb->callback(cb, from_schedule);
         }
     }
 }
 
 struct blk_plug_cb *blk_check_plugged(blk_plug_cb_fn unplug, void *data,
                       int size)
 {
     struct blk_plug *plug = current->plug;
     struct blk_plug_cb *cb;
 
     if (!plug)
         return NULL;
 
     list_for_each_entry(cb, &plug->cb_list, list)
         if (cb->callback == unplug && cb->data == data)
             return cb;
 
     /* Not currently on the callback list */
     BUG_ON(size < sizeof(*cb));
     cb = kzalloc(size, GFP_ATOMIC);
     if (cb) {
         cb->data = data;
         cb->callback = unplug;
         list_add(&cb->list, &plug->cb_list);
     }
     return cb;
 }
 EXPORT_SYMBOL(blk_check_plugged);
 
 void __blk_flush_plug(struct blk_plug *plug, bool from_schedule)
 {
     if (!list_empty(&plug->cb_list))
         flush_plug_callbacks(plug, from_schedule);
     if (!rq_list_empty(plug->mq_list))
         blk_mq_flush_plug_list(plug, from_schedule);
     /*
      * Unconditionally flush out cached requests, even if the unplug
      * event came from schedule. Since we know hold references to the
      * queue for cached requests, we don't want a blocked task holding
      * up a queue freeze/quiesce event.
      */
     if (unlikely(!rq_list_empty(plug->cached_rq)))
         blk_mq_free_plug_rqs(plug);
 }
 
 /**
  * blk_finish_plug - mark the end of a batch of submitted I/O
  * @plug:   The &struct blk_plug passed to blk_start_plug()
  *
  * Description:
  * Indicate that a batch of I/O submissions is complete.  This function
  * must be paired with an initial call to blk_start_plug().  The intent
  * is to allow the block layer to optimize I/O submission.  See the
  * documentation for blk_start_plug() for more information.
  */
 void blk_finish_plug(struct blk_plug *plug)
 {
     if (plug == current->plug) {
         __blk_flush_plug(plug, false);
         current->plug = NULL;
     }
 }
 EXPORT_SYMBOL(blk_finish_plug);
 
 void blk_io_schedule(void)
 {
     /* Prevent hang_check timer from firing at us during very long I/O */
     unsigned long timeout = sysctl_hung_task_timeout_secs * HZ / 2;
 
     if (timeout)
         io_schedule_timeout(timeout);
     else
         io_schedule();
 }
 EXPORT_SYMBOL_GPL(blk_io_schedule);
 
 int __init blk_dev_init(void)
 {
     BUILD_BUG_ON((__force u32)REQ_OP_LAST >= (1 << REQ_OP_BITS));
     BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
             sizeof_field(struct request, cmd_flags));
     BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
             sizeof_field(struct bio, bi_opf));
     BUILD_BUG_ON(ALIGN(offsetof(struct request_queue, srcu),
                __alignof__(struct request_queue)) !=
              sizeof(struct request_queue));
 
     /* used for unplugging and affects IO latency/throughput - HIGHPRI */
     kblockd_workqueue = alloc_workqueue("kblockd",
                         WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
     if (!kblockd_workqueue)
         panic("Failed to create kblockd\n");
 
     blk_requestq_cachep = kmem_cache_create("request_queue",
             sizeof(struct request_queue), 0, SLAB_PANIC, NULL);
 
     blk_requestq_srcu_cachep = kmem_cache_create("request_queue_srcu",
             sizeof(struct request_queue) +
             sizeof(struct srcu_struct), 0, SLAB_PANIC, NULL);
 
     blk_debugfs_root = debugfs_create_dir("block", NULL);
 
     return 0;
 }

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