diff options
| -rw-r--r-- | fs/block_dev.c | 198 | ||||
| -rw-r--r-- | include/linux/fs.h | 1 |
2 files changed, 175 insertions, 24 deletions
diff --git a/fs/block_dev.c b/fs/block_dev.c index e59440c7e1cf..ea8385ea58ab 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -694,11 +694,144 @@ static bool bd_may_claim(struct block_device *bdev, struct block_device *whole, } /** + * bd_prepare_to_claim - prepare to claim a block device + * @bdev: block device of interest + * @whole: the whole device containing @bdev, may equal @bdev + * @holder: holder trying to claim @bdev + * + * Prepare to claim @bdev. This function fails if @bdev is already + * claimed by another holder and waits if another claiming is in + * progress. This function doesn't actually claim. On successful + * return, the caller has ownership of bd_claiming and bd_holder[s]. + * + * CONTEXT: + * spin_lock(&bdev_lock). Might release bdev_lock, sleep and regrab + * it multiple times. + * + * RETURNS: + * 0 if @bdev can be claimed, -EBUSY otherwise. + */ +static int bd_prepare_to_claim(struct block_device *bdev, + struct block_device *whole, void *holder) +{ +retry: + /* if someone else claimed, fail */ + if (!bd_may_claim(bdev, whole, holder)) + return -EBUSY; + + /* if someone else is claiming, wait for it to finish */ + if (whole->bd_claiming && whole->bd_claiming != holder) { + wait_queue_head_t *wq = bit_waitqueue(&whole->bd_claiming, 0); + DEFINE_WAIT(wait); + + prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE); + spin_unlock(&bdev_lock); + schedule(); + finish_wait(wq, &wait); + spin_lock(&bdev_lock); + goto retry; + } + + /* yay, all mine */ + return 0; +} + +/** + * bd_start_claiming - start claiming a block device + * @bdev: block device of interest + * @holder: holder trying to claim @bdev + * + * @bdev is about to be opened exclusively. Check @bdev can be opened + * exclusively and mark that an exclusive open is in progress. Each + * successful call to this function must be matched with a call to + * either bd_claim() or bd_abort_claiming(). If this function + * succeeds, the matching bd_claim() is guaranteed to succeed. + * + * CONTEXT: + * Might sleep. + * + * RETURNS: + * Pointer to the block device containing @bdev on success, ERR_PTR() + * value on failure. + */ +static struct block_device *bd_start_claiming(struct block_device *bdev, + void *holder) +{ + struct gendisk *disk; + struct block_device *whole; + int partno, err; + + might_sleep(); + + /* + * @bdev might not have been initialized properly yet, look up + * and grab the outer block device the hard way. + */ + disk = get_gendisk(bdev->bd_dev, &partno); + if (!disk) + return ERR_PTR(-ENXIO); + + whole = bdget_disk(disk, 0); + put_disk(disk); + if (!whole) + return ERR_PTR(-ENOMEM); + + /* prepare to claim, if successful, mark claiming in progress */ + spin_lock(&bdev_lock); + + err = bd_prepare_to_claim(bdev, whole, holder); + if (err == 0) { + whole->bd_claiming = holder; + spin_unlock(&bdev_lock); + return whole; + } else { + spin_unlock(&bdev_lock); + bdput(whole); + return ERR_PTR(err); + } +} + +/* releases bdev_lock */ +static void __bd_abort_claiming(struct block_device *whole, void *holder) +{ + BUG_ON(whole->bd_claiming != holder); + whole->bd_claiming = NULL; + wake_up_bit(&whole->bd_claiming, 0); + + spin_unlock(&bdev_lock); + bdput(whole); +} + +/** + * bd_abort_claiming - abort claiming a block device + * @whole: whole block device returned by bd_start_claiming() + * @holder: holder trying to claim @bdev + * + * Abort a claiming block started by bd_start_claiming(). Note that + * @whole is not the block device to be claimed but the whole device + * returned by bd_start_claiming(). + * + * CONTEXT: + * Grabs and releases bdev_lock. + */ +static void bd_abort_claiming(struct block_device *whole, void *holder) +{ + spin_lock(&bdev_lock); + __bd_abort_claiming(whole, holder); /* releases bdev_lock */ +} + +/** * bd_claim - claim a block device * @bdev: block device to claim * @holder: holder trying to claim @bdev * - * Try to claim @bdev. + * Try to claim @bdev which must have been opened successfully. This + * function may be called with or without preceding + * blk_start_claiming(). In the former case, this function is always + * successful and terminates the claiming block. + * + * CONTEXT: + * Might sleep. * * RETURNS: * 0 if successful, -EBUSY if @bdev is already claimed. @@ -706,11 +839,14 @@ static bool bd_may_claim(struct block_device *bdev, struct block_device *whole, int bd_claim(struct block_device *bdev, void *holder) { struct block_device *whole = bdev->bd_contains; - int res = -EBUSY; + int res; + + might_sleep(); spin_lock(&bdev_lock); - if (bd_may_claim(bdev, whole, holder)) { + res = bd_prepare_to_claim(bdev, whole, holder); + if (res == 0) { /* note that for a whole device bd_holders * will be incremented twice, and bd_holder will * be set to bd_claim before being set to holder @@ -719,10 +855,13 @@ int bd_claim(struct block_device *bdev, void *holder) whole->bd_holder = bd_claim; bdev->bd_holders++; bdev->bd_holder = holder; - res = 0; } - spin_unlock(&bdev_lock); + if (whole->bd_claiming) + __bd_abort_claiming(whole, holder); /* releases bdev_lock */ + else + spin_unlock(&bdev_lock); + return res; } EXPORT_SYMBOL(bd_claim); @@ -1338,6 +1477,7 @@ EXPORT_SYMBOL(blkdev_get); static int blkdev_open(struct inode * inode, struct file * filp) { + struct block_device *whole = NULL; struct block_device *bdev; int res; @@ -1360,22 +1500,25 @@ static int blkdev_open(struct inode * inode, struct file * filp) if (bdev == NULL) return -ENOMEM; + if (filp->f_mode & FMODE_EXCL) { + whole = bd_start_claiming(bdev, filp); + if (IS_ERR(whole)) { + bdput(bdev); + return PTR_ERR(whole); + } + } + filp->f_mapping = bdev->bd_inode->i_mapping; res = blkdev_get(bdev, filp->f_mode); - if (res) - return res; - if (filp->f_mode & FMODE_EXCL) { - res = bd_claim(bdev, filp); - if (res) - goto out_blkdev_put; + if (whole) { + if (res == 0) + BUG_ON(bd_claim(bdev, filp) != 0); + else + bd_abort_claiming(whole, filp); } - return 0; - - out_blkdev_put: - blkdev_put(bdev, filp->f_mode); return res; } @@ -1586,27 +1729,34 @@ EXPORT_SYMBOL(lookup_bdev); */ struct block_device *open_bdev_exclusive(const char *path, fmode_t mode, void *holder) { - struct block_device *bdev; - int error = 0; + struct block_device *bdev, *whole; + int error; bdev = lookup_bdev(path); if (IS_ERR(bdev)) return bdev; + whole = bd_start_claiming(bdev, holder); + if (IS_ERR(whole)) { + bdput(bdev); + return whole; + } + error = blkdev_get(bdev, mode); if (error) - return ERR_PTR(error); + goto out_abort_claiming; + error = -EACCES; if ((mode & FMODE_WRITE) && bdev_read_only(bdev)) - goto blkdev_put; - error = bd_claim(bdev, holder); - if (error) - goto blkdev_put; + goto out_blkdev_put; + BUG_ON(bd_claim(bdev, holder) != 0); return bdev; - -blkdev_put: + +out_blkdev_put: blkdev_put(bdev, mode); +out_abort_claiming: + bd_abort_claiming(whole, holder); return ERR_PTR(error); } diff --git a/include/linux/fs.h b/include/linux/fs.h index 39d57bc6cc71..31ee31be51e9 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -651,6 +651,7 @@ struct block_device { int bd_openers; struct mutex bd_mutex; /* open/close mutex */ struct list_head bd_inodes; + void * bd_claiming; void * bd_holder; int bd_holders; #ifdef CONFIG_SYSFS |