From: Evan Green evgreen@chromium.org
[ Upstream commit c52abf563049e787c1341cdf15c7dbe1bfbc951b ]
If the backing device for a loop device is itself a block device, then mirror the "write zeroes" capabilities of the underlying block device into the loop device. Copy this capability into both max_write_zeroes_sectors and max_discard_sectors of the loop device.
The reason for this is that REQ_OP_DISCARD on a loop device translates into blkdev_issue_zeroout(), rather than blkdev_issue_discard(). This presents a consistent interface for loop devices (that discarded data is zeroed), regardless of the backing device type of the loop device. There should be no behavior change for loop devices backed by regular files.
This change fixes blktest block/003, and removes an extraneous error print in block/013 when testing on a loop device backed by a block device that does not support discard.
Signed-off-by: Evan Green evgreen@chromium.org Reviewed-by: Gwendal Grignou gwendal@chromium.org Reviewed-by: Chaitanya Kulkarni chaitanya.kulkarni@wdc.com [used updated version of Evan's comment in loop_config_discard()] [moved backingq to local scope, removed redundant braces] Signed-off-by: Andrzej Pietrasiewicz andrzej.p@collabora.com Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/loop.c | 42 +++++++++++++++++++++++++++++++----------- 1 file changed, 31 insertions(+), 11 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index ef6e251857c8c..57ed6b70d2950 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -427,11 +427,12 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos, * information. */ struct file *file = lo->lo_backing_file; + struct request_queue *q = lo->lo_queue; int ret;
mode |= FALLOC_FL_KEEP_SIZE;
- if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) { + if (!blk_queue_discard(q)) { ret = -EOPNOTSUPP; goto out; } @@ -863,28 +864,47 @@ static void loop_config_discard(struct loop_device *lo) struct inode *inode = file->f_mapping->host; struct request_queue *q = lo->lo_queue;
+ /* + * If the backing device is a block device, mirror its zeroing + * capability. Set the discard sectors to the block device's zeroing + * capabilities because loop discards result in blkdev_issue_zeroout(), + * not blkdev_issue_discard(). This maintains consistent behavior with + * file-backed loop devices: discarded regions read back as zero. + */ + if (S_ISBLK(inode->i_mode) && !lo->lo_encrypt_key_size) { + struct request_queue *backingq; + + backingq = bdev_get_queue(inode->i_bdev); + blk_queue_max_discard_sectors(q, + backingq->limits.max_write_zeroes_sectors); + + blk_queue_max_write_zeroes_sectors(q, + backingq->limits.max_write_zeroes_sectors); + /* * We use punch hole to reclaim the free space used by the * image a.k.a. discard. However we do not support discard if * encryption is enabled, because it may give an attacker * useful information. */ - if ((!file->f_op->fallocate) || - lo->lo_encrypt_key_size) { + } else if (!file->f_op->fallocate || lo->lo_encrypt_key_size) { q->limits.discard_granularity = 0; q->limits.discard_alignment = 0; blk_queue_max_discard_sectors(q, 0); blk_queue_max_write_zeroes_sectors(q, 0); - blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q); - return; - }
- q->limits.discard_granularity = inode->i_sb->s_blocksize; - q->limits.discard_alignment = 0; + } else { + q->limits.discard_granularity = inode->i_sb->s_blocksize; + q->limits.discard_alignment = 0;
- blk_queue_max_discard_sectors(q, UINT_MAX >> 9); - blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9); - blk_queue_flag_set(QUEUE_FLAG_DISCARD, q); + blk_queue_max_discard_sectors(q, UINT_MAX >> 9); + blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9); + } + + if (q->limits.max_write_zeroes_sectors) + blk_queue_flag_set(QUEUE_FLAG_DISCARD, q); + else + blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q); }
static void loop_unprepare_queue(struct loop_device *lo)