Additional fields were added in the block_device structure: bd_interposer and bd_interposer_lock. The bd_interposer field contains a pointer to an interposer block device. bd_interposer_lock is a lock which allows to safely attach and detach the interposer device.
New functions bdev_interposer_attach() and bdev_interposer_detach() allow to attach and detach an interposer device. But first it is required to lock the processing of bio requests by the block device with bdev_interposer_lock() function. The BIO_INTERPOSED flag means that the bio request has been already interposed. This flag avoids recursive bio request interception. Signed-off-by: Sergei Shtepa <[email protected]> --- block/genhd.c | 52 +++++++++++++++++++++++++++++++++++++++ fs/block_dev.c | 3 +++ include/linux/blk_types.h | 6 +++++ include/linux/blkdev.h | 32 ++++++++++++++++++++++++ 4 files changed, 93 insertions(+) diff --git a/block/genhd.c b/block/genhd.c index 8c8f543572e6..3ec77947b3ba 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -1938,3 +1938,55 @@ static void disk_release_events(struct gendisk *disk) WARN_ON_ONCE(disk->ev && disk->ev->block != 1); kfree(disk->ev); } + +/** + * bdev_interposer_attach - Attach an interposer block device to original + * @original: original block device + * @interposer: interposer block device + * + * Before attaching an interposer, it is necessary to lock the processing + * of bio requests of the original device by calling bdev_interposer_lock(). + * + * The bdev_interposer_detach() function allows to detach the interposer + * from the original block device. + */ +int bdev_interposer_attach(struct block_device *original, + struct block_device *interposer) +{ + struct block_device *bdev; + + WARN_ON(!original); + if (original->bd_interposer) + return -EBUSY; + + bdev = bdgrab(interposer); + if (!bdev) + return -ENODEV; + + original->bd_interposer = bdev; + return 0; +} +EXPORT_SYMBOL_GPL(bdev_interposer_attach); + +/** + * bdev_interposer_detach - Detach interposer from block device + * @original: original block device + * + * Before detaching an interposer, it is necessary to lock the processing + * of bio requests of the original device by calling bdev_interposer_lock(). + * + * The interposer should be attached using the bdev_interposer_attach() + * function. + */ +void bdev_interposer_detach(struct block_device *original) +{ + if (WARN_ON(!original)) + return; + + if (!original->bd_interposer) + return; + + bdput(original->bd_interposer); + original->bd_interposer = NULL; +} +EXPORT_SYMBOL_GPL(bdev_interposer_detach); diff --git a/fs/block_dev.c b/fs/block_dev.c index 09d6f7229db9..a98a56cc634f 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -809,6 +809,7 @@ static void bdev_free_inode(struct inode *inode) { struct block_device *bdev = I_BDEV(inode); + percpu_free_rwsem(&bdev->bd_interposer_lock); free_percpu(bdev->bd_stats); kfree(bdev->bd_meta_info); @@ -909,6 +910,8 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno) iput(inode); return NULL; } + bdev->bd_interposer = NULL; + percpu_init_rwsem(&bdev->bd_interposer_lock); return bdev; } diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index db026b6ec15a..8e4309eb3b18 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -46,6 +46,11 @@ struct block_device { spinlock_t bd_size_lock; /* for bd_inode->i_size updates */ struct gendisk * bd_disk; struct backing_dev_info *bd_bdi; + /* The interposer allows to redirect bio to another device */ + struct block_device *bd_interposer; + /* Lock the queue of block device to attach or detach interposer. + * Allows to safely suspend and flush interposer. */ + struct percpu_rw_semaphore bd_interposer_lock; /* The counter of freeze processes */ int bd_fsfreeze_count; @@ -304,6 +309,7 @@ enum { BIO_CGROUP_ACCT, /* has been accounted to a cgroup */ BIO_TRACKED, /* set if bio goes through the rq_qos path */ BIO_REMAPPED, + BIO_INTERPOSED, /* bio was reassigned to another block device */ BIO_FLAG_LAST }; diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 158aefae1030..3e38b0c40b9d 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -2029,4 +2029,36 @@ int fsync_bdev(struct block_device *bdev); int freeze_bdev(struct block_device *bdev); int thaw_bdev(struct block_device *bdev); +/** + * bdev_interposer_lock - Lock bio processing + * @bdev: locking block device + * + * Lock the bio processing in submit_bio_noacct() for the new requests in the + * original block device. Requests from the interposer will not be locked. + * + * To unlock, use the bdev_interposer_unlock() function. + * + * This lock should be used to attach/detach the interposer to the device. + */ +static inline void bdev_interposer_lock(struct block_device *bdev) +{ + percpu_down_write(&bdev->bd_interposer_lock); +} + +/** + * bdev_interposer_unlock - Unlock bio processing + * @bdev: locked block device + * + * Unlock the bio processing that was locked by bdev_interposer_lock() function. + * + * This lock should be used to attach/detach the interposer to the device. + */ +static inline void bdev_interposer_unlock(struct block_device *bdev) +{ + percpu_up_write(&bdev->bd_interposer_lock); +} + +int bdev_interposer_attach(struct block_device *original, + struct block_device *interposer); +void bdev_interposer_detach(struct block_device *original); #endif /* _LINUX_BLKDEV_H */ -- 2.20.1 -- dm-devel mailing list [email protected] https://listman.redhat.com/mailman/listinfo/dm-devel
