From 781ee863adc8347207e1dae44577401bb4128bed Mon Sep 17 00:00:00 2001 From: Evan Green Date: Tue, 22 Sep 2020 10:20:32 +0800 Subject: [PATCH] loop: Better discard support for block devices stable inclusion from linux-4.19.119 commit 012fd9ffcdf29b8a15f0de36677ebfa63920243c -------------------------------- [ 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 Reviewed-by: Gwendal Grignou Reviewed-by: Chaitanya Kulkarni [used updated version of Evan's comment in loop_config_discard()] [moved backingq to local scope, removed redundant braces] Signed-off-by: Andrzej Pietrasiewicz Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin Signed-off-by: Yang Yingliang --- 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 3f617fcea9fe..56705e1ddbce 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -426,11 +426,12 @@ 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; } @@ -864,28 +865,47 @@ 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) -- GitLab