Quelle bdev.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
*  Copyright (C) 1991, 1992  Linus Torvalds
*  Copyright (C) 2001  Andrea Arcangeli <andrea@suse.de> SuSE
*  Copyright (C) 2016 - 2020 Christoph Hellwig
*/

#include <linux/init.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/kmod.h>
#include <linux/major.h>
#include <linux/device_cgroup.h>
#include <linux/blkdev.h>
#include <linux/blk-integrity.h>
#include <linux/backing-dev.h>
#include <linux/module.h>
#include <linux/blkpg.h>
#include <linux/magic.h>
#include <linux/buffer_head.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/mount.h>
#include <linux/pseudo_fs.h>
#include <linux/uio.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/part_stat.h>
#include <linux/uaccess.h>
#include <linux/stat.h>
#include "../fs/internal.h"
#include "blk.h"

/* Should we allow writing to mounted block devices? */
static bool bdev_allow_write_mounted = IS_ENABLED(CONFIG_BLK_DEV_WRITE_MOUNTED);

struct bdev_inode {
struct block_device bdev;
struct inode vfs_inode;
};

static inline struct bdev_inode *BDEV_I(struct inode *inode)
{
return container_of(inode, struct bdev_inode, vfs_inode);
}

static inline struct inode *BD_INODE(struct block_device *bdev)
{
return &container_of(bdev, struct bdev_inode, bdev)->vfs_inode;
}

struct block_device *I_BDEV(struct inode *inode)
{
return &BDEV_I(inode)->bdev;
}
EXPORT_SYMBOL(I_BDEV);

struct block_device *file_bdev(struct file *bdev_file)
{
return I_BDEV(bdev_file->f_mapping->host);
}
EXPORT_SYMBOL(file_bdev);

static void bdev_write_inode(struct block_device *bdev)
{
struct inode *inode = BD_INODE(bdev);
int ret;

spin_lock(&inode->i_lock);
while (inode->i_state & I_DIRTY) {
  spin_unlock(&inode->i_lock);
  ret = write_inode_now(inode, true);
  if (ret)
   pr_warn_ratelimited(
"VFS: Dirty inode writeback failed for block device %pg (err=%d).\n",
    bdev, ret);
  spin_lock(&inode->i_lock);
}
spin_unlock(&inode->i_lock);
}

/* Kill _all_ buffers and pagecache , dirty or not.. */
static void kill_bdev(struct block_device *bdev)
{
struct address_space *mapping = bdev->bd_mapping;

if (mapping_empty(mapping))
  return;

invalidate_bh_lrus();
truncate_inode_pages(mapping, 0);
}

/* Invalidate clean unused buffers and pagecache. */
void invalidate_bdev(struct block_device *bdev)
{
struct address_space *mapping = bdev->bd_mapping;

if (mapping->nrpages) {
  invalidate_bh_lrus();
  lru_add_drain_all(); /* make sure all lru add caches are flushed */
  invalidate_mapping_pages(mapping, 0, -1);
}
}
EXPORT_SYMBOL(invalidate_bdev);

/*
* Drop all buffers & page cache for given bdev range. This function bails
* with error if bdev has other exclusive owner (such as filesystem).
*/
int truncate_bdev_range(struct block_device *bdev, blk_mode_t mode,
   loff_t lstart, loff_t lend)
{
/*
* If we don't hold exclusive handle for the device, upgrade to it
* while we discard the buffer cache to avoid discarding buffers
* under live filesystem.
*/
if (!(mode & BLK_OPEN_EXCL)) {
  int err = bd_prepare_to_claim(bdev, truncate_bdev_range, NULL);
  if (err)
   goto invalidate;
}

truncate_inode_pages_range(bdev->bd_mapping, lstart, lend);
if (!(mode & BLK_OPEN_EXCL))
  bd_abort_claiming(bdev, truncate_bdev_range);
return 0;

invalidate:
/*
* Someone else has handle exclusively open. Try invalidating instead.
* The 'end' argument is inclusive so the rounding is safe.
*/
return invalidate_inode_pages2_range(bdev->bd_mapping,
          lstart >> PAGE_SHIFT,
          lend >> PAGE_SHIFT);
}

static void set_init_blocksize(struct block_device *bdev)
{
unsigned int bsize = bdev_logical_block_size(bdev);
loff_t size = i_size_read(BD_INODE(bdev));

while (bsize < PAGE_SIZE) {
  if (size & bsize)
   break;
  bsize <<= 1;
}
BD_INODE(bdev)->i_blkbits = blksize_bits(bsize);
mapping_set_folio_min_order(BD_INODE(bdev)->i_mapping,
        get_order(bsize));
}

/**
* bdev_validate_blocksize - check that this block size is acceptable
* @bdev: blockdevice to check
* @block_size: block size to check
*
* For block device users that do not use buffer heads or the block device
* page cache, make sure that this block size can be used with the device.
*
* Return: On success zero is returned, negative error code on failure.
*/
int bdev_validate_blocksize(struct block_device *bdev, int block_size)
{
if (blk_validate_block_size(block_size))
  return -EINVAL;

/* Size cannot be smaller than the size supported by the device */
if (block_size < bdev_logical_block_size(bdev))
  return -EINVAL;

return 0;
}
EXPORT_SYMBOL_GPL(bdev_validate_blocksize);

int set_blocksize(struct file *file, int size)
{
struct inode *inode = file->f_mapping->host;
struct block_device *bdev = I_BDEV(inode);
int ret;

ret = bdev_validate_blocksize(bdev, size);
if (ret)
  return ret;

if (!file->private_data)
  return -EINVAL;

/* Don't change the size if it is same as current */
if (inode->i_blkbits != blksize_bits(size)) {
  /*
* Flush and truncate the pagecache before we reconfigure the
* mapping geometry because folio sizes are variable now.  If a
* reader has already allocated a folio whose size is smaller
* than the new min_order but invokes readahead after the new
* min_order becomes visible, readahead will think there are
* "zero" blocks per folio and crash.  Take the inode and
* invalidation locks to avoid racing with
* read/write/fallocate.
*/
  inode_lock(inode);
  filemap_invalidate_lock(inode->i_mapping);

  sync_blockdev(bdev);
  kill_bdev(bdev);

  inode->i_blkbits = blksize_bits(size);
  mapping_set_folio_min_order(inode->i_mapping, get_order(size));
  kill_bdev(bdev);
  filemap_invalidate_unlock(inode->i_mapping);
  inode_unlock(inode);
}
return 0;
}

EXPORT_SYMBOL(set_blocksize);

int sb_set_blocksize(struct super_block *sb, int size)
{
if (!(sb->s_type->fs_flags & FS_LBS) && size > PAGE_SIZE)
  return 0;
if (set_blocksize(sb->s_bdev_file, size))
  return 0;
/* If we get here, we know size is validated */
sb->s_blocksize = size;
sb->s_blocksize_bits = blksize_bits(size);
return sb->s_blocksize;
}

EXPORT_SYMBOL(sb_set_blocksize);

int sb_min_blocksize(struct super_block *sb, int size)
{
int minsize = bdev_logical_block_size(sb->s_bdev);
if (size < minsize)
  size = minsize;
return sb_set_blocksize(sb, size);
}

EXPORT_SYMBOL(sb_min_blocksize);

int sync_blockdev_nowait(struct block_device *bdev)
{
if (!bdev)
  return 0;
return filemap_flush(bdev->bd_mapping);
}
EXPORT_SYMBOL_GPL(sync_blockdev_nowait);

/*
* Write out and wait upon all the dirty data associated with a block
* device via its mapping.  Does not take the superblock lock.
*/
int sync_blockdev(struct block_device *bdev)
{
if (!bdev)
  return 0;
return filemap_write_and_wait(bdev->bd_mapping);
}
EXPORT_SYMBOL(sync_blockdev);

int sync_blockdev_range(struct block_device *bdev, loff_t lstart, loff_t lend)
{
return filemap_write_and_wait_range(bdev->bd_mapping,
   lstart, lend);
}
EXPORT_SYMBOL(sync_blockdev_range);

/**
* bdev_freeze - lock a filesystem and force it into a consistent state
* @bdev: blockdevice to lock
*
* If a superblock is found on this device, we take the s_umount semaphore
* on it to make sure nobody unmounts until the snapshot creation is done.
* The reference counter (bd_fsfreeze_count) guarantees that only the last
* unfreeze process can unfreeze the frozen filesystem actually when multiple
* freeze requests arrive simultaneously. It counts up in bdev_freeze() and
* count down in bdev_thaw(). When it becomes 0, thaw_bdev() will unfreeze
* actually.
*
* Return: On success zero is returned, negative error code on failure.
*/
int bdev_freeze(struct block_device *bdev)
{
int error = 0;

mutex_lock(&bdev->bd_fsfreeze_mutex);

if (atomic_inc_return(&bdev->bd_fsfreeze_count) > 1) {
  mutex_unlock(&bdev->bd_fsfreeze_mutex);
  return 0;
}

mutex_lock(&bdev->bd_holder_lock);
if (bdev->bd_holder_ops && bdev->bd_holder_ops->freeze) {
  error = bdev->bd_holder_ops->freeze(bdev);
  lockdep_assert_not_held(&bdev->bd_holder_lock);
} else {
  mutex_unlock(&bdev->bd_holder_lock);
  error = sync_blockdev(bdev);
}

if (error)
  atomic_dec(&bdev->bd_fsfreeze_count);

mutex_unlock(&bdev->bd_fsfreeze_mutex);
return error;
}
EXPORT_SYMBOL(bdev_freeze);

/**
* bdev_thaw - unlock filesystem
* @bdev: blockdevice to unlock
*
* Unlocks the filesystem and marks it writeable again after bdev_freeze().
*
* Return: On success zero is returned, negative error code on failure.
*/
int bdev_thaw(struct block_device *bdev)
{
int error = -EINVAL, nr_freeze;

mutex_lock(&bdev->bd_fsfreeze_mutex);

/*
* If this returns < 0 it means that @bd_fsfreeze_count was
* already 0 and no decrement was performed.
*/
nr_freeze = atomic_dec_if_positive(&bdev->bd_fsfreeze_count);
if (nr_freeze < 0)
  goto out;

error = 0;
if (nr_freeze > 0)
  goto out;

mutex_lock(&bdev->bd_holder_lock);
if (bdev->bd_holder_ops && bdev->bd_holder_ops->thaw) {
  error = bdev->bd_holder_ops->thaw(bdev);
  lockdep_assert_not_held(&bdev->bd_holder_lock);
} else {
  mutex_unlock(&bdev->bd_holder_lock);
}

if (error)
  atomic_inc(&bdev->bd_fsfreeze_count);
out:
mutex_unlock(&bdev->bd_fsfreeze_mutex);
return error;
}
EXPORT_SYMBOL(bdev_thaw);

/*
* pseudo-fs
*/

static  __cacheline_aligned_in_smp DEFINE_MUTEX(bdev_lock);
static struct kmem_cache *bdev_cachep __ro_after_init;

static struct inode *bdev_alloc_inode(struct super_block *sb)
{
struct bdev_inode *ei = alloc_inode_sb(sb, bdev_cachep, GFP_KERNEL);

if (!ei)
  return NULL;
memset(&ei->bdev, 0, sizeof(ei->bdev));

if (security_bdev_alloc(&ei->bdev)) {
  kmem_cache_free(bdev_cachep, ei);
  return NULL;
}
return &ei->vfs_inode;
}

static void bdev_free_inode(struct inode *inode)
{
struct block_device *bdev = I_BDEV(inode);

free_percpu(bdev->bd_stats);
kfree(bdev->bd_meta_info);
security_bdev_free(bdev);

if (!bdev_is_partition(bdev)) {
  if (bdev->bd_disk && bdev->bd_disk->bdi)
   bdi_put(bdev->bd_disk->bdi);
  kfree(bdev->bd_disk);
}

if (MAJOR(bdev->bd_dev) == BLOCK_EXT_MAJOR)
  blk_free_ext_minor(MINOR(bdev->bd_dev));

kmem_cache_free(bdev_cachep, BDEV_I(inode));
}

static void init_once(void *data)
{
struct bdev_inode *ei = data;

inode_init_once(&ei->vfs_inode);
}

static void bdev_evict_inode(struct inode *inode)
{
truncate_inode_pages_final(&inode->i_data);
invalidate_inode_buffers(inode); /* is it needed here? */
clear_inode(inode);
}

static const struct super_operations bdev_sops = {
.statfs = simple_statfs,
.alloc_inode = bdev_alloc_inode,
.free_inode = bdev_free_inode,
.drop_inode = generic_delete_inode,
.evict_inode = bdev_evict_inode,
};

static int bd_init_fs_context(struct fs_context *fc)
{
struct pseudo_fs_context *ctx = init_pseudo(fc, BDEVFS_MAGIC);
if (!ctx)
  return -ENOMEM;
fc->s_iflags |= SB_I_CGROUPWB;
ctx->ops = &bdev_sops;
return 0;
}

static struct file_system_type bd_type = {
.name  = "bdev",
.init_fs_context = bd_init_fs_context,
.kill_sb = kill_anon_super,
};

struct super_block *blockdev_superblock __ro_after_init;
static struct vfsmount *blockdev_mnt __ro_after_init;
EXPORT_SYMBOL_GPL(blockdev_superblock);

void __init bdev_cache_init(void)
{
int err;

bdev_cachep = kmem_cache_create("bdev_cache", sizeof(struct bdev_inode),
   0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
    SLAB_ACCOUNT|SLAB_PANIC),
   init_once);
err = register_filesystem(&bd_type);
if (err)
  panic("Cannot register bdev pseudo-fs");
blockdev_mnt = kern_mount(&bd_type);
if (IS_ERR(blockdev_mnt))
  panic("Cannot create bdev pseudo-fs");
blockdev_superblock = blockdev_mnt->mnt_sb;   /* For writeback */
}

struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
{
struct block_device *bdev;
struct inode *inode;

inode = new_inode(blockdev_superblock);
if (!inode)
  return NULL;
inode->i_mode = S_IFBLK;
inode->i_rdev = 0;
inode->i_data.a_ops = &def_blk_aops;
mapping_set_gfp_mask(&inode->i_data, GFP_USER);

bdev = I_BDEV(inode);
mutex_init(&bdev->bd_fsfreeze_mutex);
spin_lock_init(&bdev->bd_size_lock);
mutex_init(&bdev->bd_holder_lock);
atomic_set(&bdev->__bd_flags, partno);
bdev->bd_mapping = &inode->i_data;
bdev->bd_queue = disk->queue;
if (partno && bdev_test_flag(disk->part0, BD_HAS_SUBMIT_BIO))
  bdev_set_flag(bdev, BD_HAS_SUBMIT_BIO);
bdev->bd_stats = alloc_percpu(struct disk_stats);
if (!bdev->bd_stats) {
  iput(inode);
  return NULL;
}
bdev->bd_disk = disk;
return bdev;
}

void bdev_set_nr_sectors(struct block_device *bdev, sector_t sectors)
{
spin_lock(&bdev->bd_size_lock);
i_size_write(BD_INODE(bdev), (loff_t)sectors << SECTOR_SHIFT);
bdev->bd_nr_sectors = sectors;
spin_unlock(&bdev->bd_size_lock);
}

void bdev_add(struct block_device *bdev, dev_t dev)
{
struct inode *inode = BD_INODE(bdev);
if (bdev_stable_writes(bdev))
  mapping_set_stable_writes(bdev->bd_mapping);
bdev->bd_dev = dev;
inode->i_rdev = dev;
inode->i_ino = dev;
insert_inode_hash(inode);
}

void bdev_unhash(struct block_device *bdev)
{
remove_inode_hash(BD_INODE(bdev));
}

void bdev_drop(struct block_device *bdev)
{
iput(BD_INODE(bdev));
}

long nr_blockdev_pages(void)
{
struct inode *inode;
long ret = 0;

spin_lock(&blockdev_superblock->s_inode_list_lock);
list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list)
  ret += inode->i_mapping->nrpages;
spin_unlock(&blockdev_superblock->s_inode_list_lock);

return ret;
}

/**
* bd_may_claim - test whether a block device can be claimed
* @bdev: block device of interest
* @holder: holder trying to claim @bdev
* @hops: holder ops
*
* Test whether @bdev can be claimed by @holder.
*
* RETURNS:
* %true if @bdev can be claimed, %false otherwise.
*/
static bool bd_may_claim(struct block_device *bdev, void *holder,
  const struct blk_holder_ops *hops)
{
struct block_device *whole = bdev_whole(bdev);

lockdep_assert_held(&bdev_lock);

if (bdev->bd_holder) {
  /*
* The same holder can always re-claim.
*/
  if (bdev->bd_holder == holder) {
   if (WARN_ON_ONCE(bdev->bd_holder_ops != hops))
    return false;
   return true;
  }
  return false;
}

/*
* If the whole devices holder is set to bd_may_claim, a partition on
* the device is claimed, but not the whole device.
*/
if (whole != bdev &&
     whole->bd_holder && whole->bd_holder != bd_may_claim)
  return false;
return true;
}

/**
* bd_prepare_to_claim - claim a block device
* @bdev: block device of interest
* @holder: holder trying to claim @bdev
* @hops: holder ops.
*
* Claim @bdev.  This function fails if @bdev is already claimed by another
* holder and waits if another claiming is in progress. return, the caller
* has ownership of bd_claiming and bd_holder[s].
*
* RETURNS:
* 0 if @bdev can be claimed, -EBUSY otherwise.
*/
int bd_prepare_to_claim(struct block_device *bdev, void *holder,
  const struct blk_holder_ops *hops)
{
struct block_device *whole = bdev_whole(bdev);

if (WARN_ON_ONCE(!holder))
  return -EINVAL;
retry:
mutex_lock(&bdev_lock);
/* if someone else claimed, fail */
if (!bd_may_claim(bdev, holder, hops)) {
  mutex_unlock(&bdev_lock);
  return -EBUSY;
}

/* if claiming is already in progress, wait for it to finish */
if (whole->bd_claiming) {
  wait_queue_head_t *wq = __var_waitqueue(&whole->bd_claiming);
  DEFINE_WAIT(wait);

  prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
  mutex_unlock(&bdev_lock);
  schedule();
  finish_wait(wq, &wait);
  goto retry;
}

/* yay, all mine */
whole->bd_claiming = holder;
mutex_unlock(&bdev_lock);
return 0;
}
EXPORT_SYMBOL_GPL(bd_prepare_to_claim); /* only for the loop driver */

static void bd_clear_claiming(struct block_device *whole, void *holder)
{
lockdep_assert_held(&bdev_lock);
/* tell others that we're done */
BUG_ON(whole->bd_claiming != holder);
whole->bd_claiming = NULL;
wake_up_var(&whole->bd_claiming);
}

/**
* bd_finish_claiming - finish claiming of a block device
* @bdev: block device of interest
* @holder: holder that has claimed @bdev
* @hops: block device holder operations
*
* Finish exclusive open of a block device. Mark the device as exlusively
* open by the holder and wake up all waiters for exclusive open to finish.
*/
static void bd_finish_claiming(struct block_device *bdev, void *holder,
  const struct blk_holder_ops *hops)
{
struct block_device *whole = bdev_whole(bdev);

mutex_lock(&bdev_lock);
BUG_ON(!bd_may_claim(bdev, holder, hops));
/*
* Note that for a whole device bd_holders will be incremented twice,
* and bd_holder will be set to bd_may_claim before being set to holder
*/
whole->bd_holders++;
whole->bd_holder = bd_may_claim;
bdev->bd_holders++;
mutex_lock(&bdev->bd_holder_lock);
bdev->bd_holder = holder;
bdev->bd_holder_ops = hops;
mutex_unlock(&bdev->bd_holder_lock);
bd_clear_claiming(whole, holder);
mutex_unlock(&bdev_lock);
}

/**
* bd_abort_claiming - abort claiming of a block device
* @bdev: block device of interest
* @holder: holder that has claimed @bdev
*
* Abort claiming of a block device when the exclusive open failed. This can be
* also used when exclusive open is not actually desired and we just needed
* to block other exclusive openers for a while.
*/
void bd_abort_claiming(struct block_device *bdev, void *holder)
{
mutex_lock(&bdev_lock);
bd_clear_claiming(bdev_whole(bdev), holder);
mutex_unlock(&bdev_lock);
}
EXPORT_SYMBOL(bd_abort_claiming);

static void bd_end_claim(struct block_device *bdev, void *holder)
{
struct block_device *whole = bdev_whole(bdev);
bool unblock = false;

/*
* Release a claim on the device.  The holder fields are protected with
* bdev_lock.  open_mutex is used to synchronize disk_holder unlinking.
*/
mutex_lock(&bdev_lock);
WARN_ON_ONCE(bdev->bd_holder != holder);
WARN_ON_ONCE(--bdev->bd_holders < 0);
WARN_ON_ONCE(--whole->bd_holders < 0);
if (!bdev->bd_holders) {
  mutex_lock(&bdev->bd_holder_lock);
  bdev->bd_holder = NULL;
  bdev->bd_holder_ops = NULL;
  mutex_unlock(&bdev->bd_holder_lock);
  if (bdev_test_flag(bdev, BD_WRITE_HOLDER))
   unblock = true;
}
if (!whole->bd_holders)
  whole->bd_holder = NULL;
mutex_unlock(&bdev_lock);

/*
* If this was the last claim, remove holder link and unblock evpoll if
* it was a write holder.
*/
if (unblock) {
  disk_unblock_events(bdev->bd_disk);
  bdev_clear_flag(bdev, BD_WRITE_HOLDER);
}
}

static void blkdev_flush_mapping(struct block_device *bdev)
{
WARN_ON_ONCE(bdev->bd_holders);
sync_blockdev(bdev);
kill_bdev(bdev);
bdev_write_inode(bdev);
}

static void blkdev_put_whole(struct block_device *bdev)
{
if (atomic_dec_and_test(&bdev->bd_openers))
  blkdev_flush_mapping(bdev);
if (bdev->bd_disk->fops->release)
  bdev->bd_disk->fops->release(bdev->bd_disk);
}

static int blkdev_get_whole(struct block_device *bdev, blk_mode_t mode)
{
struct gendisk *disk = bdev->bd_disk;
int ret;

if (disk->fops->open) {
  ret = disk->fops->open(disk, mode);
  if (ret) {
   /* avoid ghost partitions on a removed medium */
   if (ret == -ENOMEDIUM &&
        test_bit(GD_NEED_PART_SCAN, &disk->state))
    bdev_disk_changed(disk, true);
   return ret;
  }
}

if (!atomic_read(&bdev->bd_openers))
  set_init_blocksize(bdev);
atomic_inc(&bdev->bd_openers);
if (test_bit(GD_NEED_PART_SCAN, &disk->state)) {
  /*
* Only return scanning errors if we are called from contexts
* that explicitly want them, e.g. the BLKRRPART ioctl.
*/
  ret = bdev_disk_changed(disk, false);
  if (ret && (mode & BLK_OPEN_STRICT_SCAN)) {
   blkdev_put_whole(bdev);
   return ret;
  }
}
return 0;
}

static int blkdev_get_part(struct block_device *part, blk_mode_t mode)
{
struct gendisk *disk = part->bd_disk;
int ret;

ret = blkdev_get_whole(bdev_whole(part), mode);
if (ret)
  return ret;

ret = -ENXIO;
if (!bdev_nr_sectors(part))
  goto out_blkdev_put;

if (!atomic_read(&part->bd_openers)) {
  disk->open_partitions++;
  set_init_blocksize(part);
}
atomic_inc(&part->bd_openers);
return 0;

out_blkdev_put:
blkdev_put_whole(bdev_whole(part));
return ret;
}

int bdev_permission(dev_t dev, blk_mode_t mode, void *holder)
{
int ret;

ret = devcgroup_check_permission(DEVCG_DEV_BLOCK,
   MAJOR(dev), MINOR(dev),
   ((mode & BLK_OPEN_READ) ? DEVCG_ACC_READ : 0) |
   ((mode & BLK_OPEN_WRITE) ? DEVCG_ACC_WRITE : 0));
if (ret)
  return ret;

/* Blocking writes requires exclusive opener */
if (mode & BLK_OPEN_RESTRICT_WRITES && !holder)
  return -EINVAL;

/*
* We're using error pointers to indicate to ->release() when we
* failed to open that block device. Also this doesn't make sense.
*/
if (WARN_ON_ONCE(IS_ERR(holder)))
  return -EINVAL;

return 0;
}

static void blkdev_put_part(struct block_device *part)
{
struct block_device *whole = bdev_whole(part);

if (atomic_dec_and_test(&part->bd_openers)) {
  blkdev_flush_mapping(part);
  whole->bd_disk->open_partitions--;
}
blkdev_put_whole(whole);
}

struct block_device *blkdev_get_no_open(dev_t dev, bool autoload)
{
struct block_device *bdev;
struct inode *inode;

inode = ilookup(blockdev_superblock, dev);
if (!inode && autoload && IS_ENABLED(CONFIG_BLOCK_LEGACY_AUTOLOAD)) {
  blk_request_module(dev);
  inode = ilookup(blockdev_superblock, dev);
  if (inode)
   pr_warn_ratelimited(
"block device autoloading is deprecated and will be removed.\n");
}
if (!inode)
  return NULL;

/* switch from the inode reference to a device mode one: */
bdev = &BDEV_I(inode)->bdev;
if (!kobject_get_unless_zero(&bdev->bd_device.kobj))
  bdev = NULL;
iput(inode);
return bdev;
}

void blkdev_put_no_open(struct block_device *bdev)
{
put_device(&bdev->bd_device);
}

static bool bdev_writes_blocked(struct block_device *bdev)
{
return bdev->bd_writers < 0;
}

static void bdev_block_writes(struct block_device *bdev)
{
bdev->bd_writers--;
}

static void bdev_unblock_writes(struct block_device *bdev)
{
bdev->bd_writers++;
}

static bool bdev_may_open(struct block_device *bdev, blk_mode_t mode)
{
if (bdev_allow_write_mounted)
  return true;
/* Writes blocked? */
if (mode & BLK_OPEN_WRITE && bdev_writes_blocked(bdev))
  return false;
if (mode & BLK_OPEN_RESTRICT_WRITES && bdev->bd_writers > 0)
  return false;
return true;
}

static void bdev_claim_write_access(struct block_device *bdev, blk_mode_t mode)
{
if (bdev_allow_write_mounted)
  return;

/* Claim exclusive or shared write access. */
if (mode & BLK_OPEN_RESTRICT_WRITES)
  bdev_block_writes(bdev);
else if (mode & BLK_OPEN_WRITE)
  bdev->bd_writers++;
}

static inline bool bdev_unclaimed(const struct file *bdev_file)
{
return bdev_file->private_data == BDEV_I(bdev_file->f_mapping->host);
}

static void bdev_yield_write_access(struct file *bdev_file)
{
struct block_device *bdev;

if (bdev_allow_write_mounted)
  return;

if (bdev_unclaimed(bdev_file))
  return;

bdev = file_bdev(bdev_file);

if (bdev_file->f_mode & FMODE_WRITE_RESTRICTED)
  bdev_unblock_writes(bdev);
else if (bdev_file->f_mode & FMODE_WRITE)
  bdev->bd_writers--;
}

/**
* bdev_open - open a block device
* @bdev: block device to open
* @mode: open mode (BLK_OPEN_*)
* @holder: exclusive holder identifier
* @hops: holder operations
* @bdev_file: file for the block device
*
* Open the block device. If @holder is not %NULL, the block device is opened
* with exclusive access.  Exclusive opens may nest for the same @holder.
*
* CONTEXT:
* Might sleep.
*
* RETURNS:
* zero on success, -errno on failure.
*/
int bdev_open(struct block_device *bdev, blk_mode_t mode, void *holder,
       const struct blk_holder_ops *hops, struct file *bdev_file)
{
bool unblock_events = true;
struct gendisk *disk = bdev->bd_disk;
int ret;

if (holder) {
  mode |= BLK_OPEN_EXCL;
  ret = bd_prepare_to_claim(bdev, holder, hops);
  if (ret)
   return ret;
} else {
  if (WARN_ON_ONCE(mode & BLK_OPEN_EXCL))
   return -EIO;
}

disk_block_events(disk);

mutex_lock(&disk->open_mutex);
ret = -ENXIO;
if (!disk_live(disk))
  goto abort_claiming;
if (!try_module_get(disk->fops->owner))
  goto abort_claiming;
ret = -EBUSY;
if (!bdev_may_open(bdev, mode))
  goto put_module;
if (bdev_is_partition(bdev))
  ret = blkdev_get_part(bdev, mode);
else
  ret = blkdev_get_whole(bdev, mode);
if (ret)
  goto put_module;
bdev_claim_write_access(bdev, mode);
if (holder) {
  bd_finish_claiming(bdev, holder, hops);

  /*
* Block event polling for write claims if requested.  Any write
* holder makes the write_holder state stick until all are
* released.  This is good enough and tracking individual
* writeable reference is too fragile given the way @mode is
* used in blkdev_get/put().
*/
  if ((mode & BLK_OPEN_WRITE) &&
      !bdev_test_flag(bdev, BD_WRITE_HOLDER) &&
      (disk->event_flags & DISK_EVENT_FLAG_BLOCK_ON_EXCL_WRITE)) {
   bdev_set_flag(bdev, BD_WRITE_HOLDER);
   unblock_events = false;
  }
}
mutex_unlock(&disk->open_mutex);

if (unblock_events)
  disk_unblock_events(disk);

bdev_file->f_flags |= O_LARGEFILE;
bdev_file->f_mode |= FMODE_CAN_ODIRECT;
if (bdev_nowait(bdev))
  bdev_file->f_mode |= FMODE_NOWAIT;
if (mode & BLK_OPEN_RESTRICT_WRITES)
  bdev_file->f_mode |= FMODE_WRITE_RESTRICTED;
bdev_file->f_mapping = bdev->bd_mapping;
bdev_file->f_wb_err = filemap_sample_wb_err(bdev_file->f_mapping);
bdev_file->private_data = holder;

return 0;
put_module:
module_put(disk->fops->owner);
abort_claiming:
if (holder)
  bd_abort_claiming(bdev, holder);
mutex_unlock(&disk->open_mutex);
disk_unblock_events(disk);
return ret;
}

/*
* If BLK_OPEN_WRITE_IOCTL is set then this is a historical quirk
* associated with the floppy driver where it has allowed ioctls if the
* file was opened for writing, but does not allow reads or writes.
* Make sure that this quirk is reflected in @f_flags.
*
* It can also happen if a block device is opened as O_RDWR | O_WRONLY.
*/
static unsigned blk_to_file_flags(blk_mode_t mode)
{
unsigned int flags = 0;

if ((mode & (BLK_OPEN_READ | BLK_OPEN_WRITE)) ==
     (BLK_OPEN_READ | BLK_OPEN_WRITE))
  flags |= O_RDWR;
else if (mode & BLK_OPEN_WRITE_IOCTL)
  flags |= O_RDWR | O_WRONLY;
else if (mode & BLK_OPEN_WRITE)
  flags |= O_WRONLY;
else if (mode & BLK_OPEN_READ)
  flags |= O_RDONLY; /* homeopathic, because O_RDONLY is 0 */
else
  WARN_ON_ONCE(true);

if (mode & BLK_OPEN_NDELAY)
  flags |= O_NDELAY;

return flags;
}

struct file *bdev_file_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
       const struct blk_holder_ops *hops)
{
struct file *bdev_file;
struct block_device *bdev;
unsigned int flags;
int ret;

ret = bdev_permission(dev, mode, holder);
if (ret)
  return ERR_PTR(ret);

bdev = blkdev_get_no_open(dev, true);
if (!bdev)
  return ERR_PTR(-ENXIO);

flags = blk_to_file_flags(mode);
bdev_file = alloc_file_pseudo_noaccount(BD_INODE(bdev),
   blockdev_mnt, "", flags | O_LARGEFILE, &def_blk_fops);
if (IS_ERR(bdev_file)) {
  blkdev_put_no_open(bdev);
  return bdev_file;
}
ihold(BD_INODE(bdev));

ret = bdev_open(bdev, mode, holder, hops, bdev_file);
if (ret) {
  /* We failed to open the block device. Let ->release() know. */
  bdev_file->private_data = ERR_PTR(ret);
  fput(bdev_file);
  return ERR_PTR(ret);
}
return bdev_file;
}
EXPORT_SYMBOL(bdev_file_open_by_dev);

struct file *bdev_file_open_by_path(const char *path, blk_mode_t mode,
        void *holder,
        const struct blk_holder_ops *hops)
{
struct file *file;
dev_t dev;
int error;

error = lookup_bdev(path, &dev);
if (error)
  return ERR_PTR(error);

file = bdev_file_open_by_dev(dev, mode, holder, hops);
if (!IS_ERR(file) && (mode & BLK_OPEN_WRITE)) {
  if (bdev_read_only(file_bdev(file))) {
   fput(file);
   file = ERR_PTR(-EACCES);
  }
}

return file;
}
EXPORT_SYMBOL(bdev_file_open_by_path);

static inline void bd_yield_claim(struct file *bdev_file)
{
struct block_device *bdev = file_bdev(bdev_file);
void *holder = bdev_file->private_data;

lockdep_assert_held(&bdev->bd_disk->open_mutex);

if (WARN_ON_ONCE(IS_ERR_OR_NULL(holder)))
  return;

if (!bdev_unclaimed(bdev_file))
  bd_end_claim(bdev, holder);
}

void bdev_release(struct file *bdev_file)
{
struct block_device *bdev = file_bdev(bdev_file);
void *holder = bdev_file->private_data;
struct gendisk *disk = bdev->bd_disk;

/* We failed to open that block device. */
if (IS_ERR(holder))
  goto put_no_open;

/*
* Sync early if it looks like we're the last one.  If someone else
* opens the block device between now and the decrement of bd_openers
* then we did a sync that we didn't need to, but that's not the end
* of the world and we want to avoid long (could be several minute)
* syncs while holding the mutex.
*/
if (atomic_read(&bdev->bd_openers) == 1)
  sync_blockdev(bdev);

mutex_lock(&disk->open_mutex);
bdev_yield_write_access(bdev_file);

if (holder)
  bd_yield_claim(bdev_file);

/*
* Trigger event checking and tell drivers to flush MEDIA_CHANGE
* event.  This is to ensure detection of media removal commanded
* from userland - e.g. eject(1).
*/
disk_flush_events(disk, DISK_EVENT_MEDIA_CHANGE);

if (bdev_is_partition(bdev))
  blkdev_put_part(bdev);
else
  blkdev_put_whole(bdev);
mutex_unlock(&disk->open_mutex);

module_put(disk->fops->owner);
put_no_open:
blkdev_put_no_open(bdev);
}

/**
* bdev_fput - yield claim to the block device and put the file
* @bdev_file: open block device
*
* Yield claim on the block device and put the file. Ensure that the
* block device can be reclaimed before the file is closed which is a
* deferred operation.
*/
void bdev_fput(struct file *bdev_file)
{
if (WARN_ON_ONCE(bdev_file->f_op != &def_blk_fops))
  return;

if (bdev_file->private_data) {
  struct block_device *bdev = file_bdev(bdev_file);
  struct gendisk *disk = bdev->bd_disk;

  mutex_lock(&disk->open_mutex);
  bdev_yield_write_access(bdev_file);
  bd_yield_claim(bdev_file);
  /*
* Tell release we already gave up our hold on the
* device and if write restrictions are available that
* we already gave up write access to the device.
*/
  bdev_file->private_data = BDEV_I(bdev_file->f_mapping->host);
  mutex_unlock(&disk->open_mutex);
}

fput(bdev_file);
}
EXPORT_SYMBOL(bdev_fput);

/**
* lookup_bdev() - Look up a struct block_device by name.
* @pathname: Name of the block device in the filesystem.
* @dev: Pointer to the block device's dev_t, if found.
*
* Lookup the block device's dev_t at @pathname in the current
* namespace if possible and return it in @dev.
*
* Context: May sleep.
* Return: 0 if succeeded, negative errno otherwise.
*/
int lookup_bdev(const char *pathname, dev_t *dev)
{
struct inode *inode;
struct path path;
int error;

if (!pathname || !*pathname)
  return -EINVAL;

error = kern_path(pathname, LOOKUP_FOLLOW, &path);
if (error)
  return error;

inode = d_backing_inode(path.dentry);
error = -ENOTBLK;
if (!S_ISBLK(inode->i_mode))
  goto out_path_put;
error = -EACCES;
if (!may_open_dev(&path))
  goto out_path_put;

*dev = inode->i_rdev;
error = 0;
out_path_put:
path_put(&path);
return error;
}
EXPORT_SYMBOL(lookup_bdev);

/**
* bdev_mark_dead - mark a block device as dead
* @bdev: block device to operate on
* @surprise: indicate a surprise removal
*
* Tell the file system that this devices or media is dead.  If @surprise is set
* to %true the device or media is already gone, if not we are preparing for an
* orderly removal.
*
* This calls into the file system, which then typicall syncs out all dirty data
* and writes back inodes and then invalidates any cached data in the inodes on
* the file system.  In addition we also invalidate the block device mapping.
*/
void bdev_mark_dead(struct block_device *bdev, bool surprise)
{
mutex_lock(&bdev->bd_holder_lock);
if (bdev->bd_holder_ops && bdev->bd_holder_ops->mark_dead)
  bdev->bd_holder_ops->mark_dead(bdev, surprise);
else {
  mutex_unlock(&bdev->bd_holder_lock);
  sync_blockdev(bdev);
}

invalidate_bdev(bdev);
}
/*
* New drivers should not use this directly.  There are some drivers however
* that needs this for historical reasons. For example, the DASD driver has
* historically had a shutdown to offline mode that doesn't actually remove the
* gendisk that otherwise looks a lot like a safe device removal.
*/
EXPORT_SYMBOL_GPL(bdev_mark_dead);

void sync_bdevs(bool wait)
{
struct inode *inode, *old_inode = NULL;

spin_lock(&blockdev_superblock->s_inode_list_lock);
list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) {
  struct address_space *mapping = inode->i_mapping;
  struct block_device *bdev;

  spin_lock(&inode->i_lock);
  if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW) ||
      mapping->nrpages == 0) {
   spin_unlock(&inode->i_lock);
   continue;
  }
  __iget(inode);
  spin_unlock(&inode->i_lock);
  spin_unlock(&blockdev_superblock->s_inode_list_lock);
  /*
* We hold a reference to 'inode' so it couldn't have been
* removed from s_inodes list while we dropped the
* s_inode_list_lock  We cannot iput the inode now as we can
* be holding the last reference and we cannot iput it under
* s_inode_list_lock. So we keep the reference and iput it
* later.
*/
  iput(old_inode);
  old_inode = inode;
  bdev = I_BDEV(inode);

  mutex_lock(&bdev->bd_disk->open_mutex);
  if (!atomic_read(&bdev->bd_openers)) {
   ; /* skip */
  } else if (wait) {
   /*
* We keep the error status of individual mapping so
* that applications can catch the writeback error using
* fsync(2). See filemap_fdatawait_keep_errors() for
* details.
*/
   filemap_fdatawait_keep_errors(inode->i_mapping);
  } else {
   filemap_fdatawrite(inode->i_mapping);
  }
  mutex_unlock(&bdev->bd_disk->open_mutex);

  spin_lock(&blockdev_superblock->s_inode_list_lock);
}
spin_unlock(&blockdev_superblock->s_inode_list_lock);
iput(old_inode);
}

/*
* Handle STATX_{DIOALIGN, WRITE_ATOMIC} for block devices.
*/
void bdev_statx(const struct path *path, struct kstat *stat, u32 request_mask)
{
struct block_device *bdev;

/*
* Note that d_backing_inode() returns the block device node inode, not
* the block device's internal inode.  Therefore it is *not* valid to
* use I_BDEV() here; the block device has to be looked up by i_rdev
* instead.
*/
bdev = blkdev_get_no_open(d_backing_inode(path->dentry)->i_rdev, false);
if (!bdev)
  return;

if (request_mask & STATX_DIOALIGN) {
  stat->dio_mem_align = bdev_dma_alignment(bdev) + 1;
  stat->dio_offset_align = bdev_logical_block_size(bdev);
  stat->result_mask |= STATX_DIOALIGN;
}

if (request_mask & STATX_WRITE_ATOMIC && bdev_can_atomic_write(bdev)) {
  struct request_queue *bd_queue = bdev->bd_queue;

  generic_fill_statx_atomic_writes(stat,
   queue_atomic_write_unit_min_bytes(bd_queue),
   queue_atomic_write_unit_max_bytes(bd_queue),
   0);
}

stat->blksize = bdev_io_min(bdev);

blkdev_put_no_open(bdev);
}

bool disk_live(struct gendisk *disk)
{
return !inode_unhashed(BD_INODE(disk->part0));
}
EXPORT_SYMBOL_GPL(disk_live);

unsigned int block_size(struct block_device *bdev)
{
return 1 << BD_INODE(bdev)->i_blkbits;
}
EXPORT_SYMBOL_GPL(block_size);

static int __init setup_bdev_allow_write_mounted(char *str)
{
if (kstrtobool(str, &bdev_allow_write_mounted))
  pr_warn("Invalid option string for bdev_allow_write_mounted:"
   " '%s'\n", str);
return 1;
}
__setup("bdev_allow_write_mounted=", setup_bdev_allow_write_mounted);

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