The newly added blkdev_get_file() function allows kernel code to create a struct file for any block device. The main use-case is for the struct file to be exposed to userspace as a file descriptor. A future patch will modify the DM_DEV_CREATE_CREATE ioctl to allow userspace to get a file descriptor to the newly created block device, avoiding nasty race conditions. Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx> --- block/bdev.c | 77 +++++++++++++++++++++++++++++++++++------- include/linux/blkdev.h | 5 +++ 2 files changed, 70 insertions(+), 12 deletions(-) diff --git a/block/bdev.c b/block/bdev.c index edc110d90df4041e7d337976951bd0d17525f1f7..09cb5ef900ca9ad5b21250bb63e64cc2a79f9289 100644 --- a/block/bdev.c +++ b/block/bdev.c @@ -459,10 +459,33 @@ static struct file_system_type bd_type = { struct super_block *blockdev_superblock __read_mostly; EXPORT_SYMBOL_GPL(blockdev_superblock); +static struct vfsmount *bd_mnt __read_mostly; + +struct file * +blkdev_get_file(struct block_device *bdev, fmode_t flags, void *holder) +{ + struct inode *inode; + struct file *filp; + int ret; + + ret = blkdev_do_open(bdev, flags, holder); + if (ret) + return ERR_PTR(ret); + inode = bdev->bd_inode; + filp = alloc_file_pseudo(inode, bd_mnt, "[block]", flags | O_CLOEXEC, &def_blk_fops); + if (IS_ERR(filp)) { + blkdev_put(bdev, flags); + } else { + filp->f_mapping = inode->i_mapping; + filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping); + } + return filp; +} +EXPORT_SYMBOL(blkdev_get_file); + void __init bdev_cache_init(void) { int err; - static struct vfsmount *bd_mnt; bdev_cachep = kmem_cache_create("bdev_cache", sizeof(struct bdev_inode), 0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT| @@ -775,7 +798,7 @@ void blkdev_put_no_open(struct block_device *bdev) * * Use this interface ONLY if you really do not have anything better - i.e. when * you are behind a truly sucky interface and all you are given is a device - * number. Everything else should use blkdev_get_by_path(). + * number. Everything else should use blkdev_get_by_path() or blkdev_do_open(). * * CONTEXT: * Might sleep. @@ -785,9 +808,7 @@ void blkdev_put_no_open(struct block_device *bdev) */ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder) { - bool unblock_events = true; struct block_device *bdev; - struct gendisk *disk; int ret; ret = devcgroup_check_permission(DEVCG_DEV_BLOCK, @@ -800,18 +821,52 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder) bdev = blkdev_get_no_open(dev); if (!bdev) return ERR_PTR(-ENXIO); - disk = bdev->bd_disk; + + ret = blkdev_do_open(bdev, mode, holder); + if (ret) { + blkdev_put_no_open(bdev); + return ERR_PTR(ret); + } + + return bdev; +} +EXPORT_SYMBOL(blkdev_get_by_dev); + +/** + * blkdev_do_open - open a block device by device pointer + * @bdev: pointer to the device to open + * @mode: FMODE_* mask + * @holder: exclusive holder identifier + * + * Open the block device pointed to by @bdev. If @mode includes + * %FMODE_EXCL, the block device is opened with exclusive access. Specifying + * %FMODE_EXCL with a %NULL @holder is invalid. Exclusive opens may nest for + * the same @holder. + * + * Unlike blkdev_get_by_dev() and bldev_get_by_path(), this function does not + * do any permission checks. The most common use-case is where the device + * was freshly created by userspace. + * + * CONTEXT: + * Might sleep. + * + * RETURNS: + * Reference 0 on success, -errno on failure. + */ +int blkdev_do_open(struct block_device *bdev, fmode_t mode, void *holder) { + struct gendisk *disk = bdev->bd_disk; + int ret = -ENXIO; + bool unblock_events = true; if (mode & FMODE_EXCL) { ret = bd_prepare_to_claim(bdev, holder); if (ret) - goto put_blkdev; + return ret; } 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)) @@ -842,7 +897,7 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder) if (unblock_events) disk_unblock_events(disk); - return bdev; + return 0; put_module: module_put(disk->fops->owner); abort_claiming: @@ -850,11 +905,9 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder) bd_abort_claiming(bdev, holder); mutex_unlock(&disk->open_mutex); disk_unblock_events(disk); -put_blkdev: - blkdev_put_no_open(bdev); - return ERR_PTR(ret); + return ret; } -EXPORT_SYMBOL(blkdev_get_by_dev); +EXPORT_SYMBOL(blkdev_do_open); /** * blkdev_get_by_path - open a block device by name diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 43d4e073b1115e4628a001081fbf08b296d342df..04635cb5ee29d22394a34c65eb34bea4e7847d8d 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -325,6 +325,11 @@ typedef int (*report_zones_cb)(struct blk_zone *zone, unsigned int idx, void disk_set_zoned(struct gendisk *disk, enum blk_zoned_model model); +struct file * +blkdev_get_file(struct block_device *bdev, fmode_t flags, void *holder); + +int blkdev_do_open(struct block_device *bdev, fmode_t flags, void *holder); + #ifdef CONFIG_BLK_DEV_ZONED #define BLK_ALL_ZONES ((unsigned int)-1) -- Sincerely, Demi Marie Obenour (she/her/hers) Invisible Things Lab