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- From 3117c3f45edbcc269baaebd3d13f39b7bf884aa6 Mon Sep 17 00:00:00 2001
- From: Evan Green <[email protected]>
- Date: Thu, 14 Nov 2019 15:50:08 -0800
- Subject: loop: Better discard support for block devices
- 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 <[email protected]>
- Reviewed-by: Gwendal Grignou <[email protected]>
- Reviewed-by: Chaitanya Kulkarni <[email protected]>
- ---
- drivers/block/loop.c | 40 +++++++++++++++++++++++++++++-----------
- 1 file changed, 29 insertions(+), 11 deletions(-)
- --- a/drivers/block/loop.c
- +++ b/drivers/block/loop.c
- @@ -426,11 +426,12 @@ static int lo_fallocate(struct loop_devi
- * 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;
- }
- @@ -863,6 +864,21 @@ static void loop_config_discard(struct l
- struct file *file = lo->lo_backing_file;
- struct inode *inode = file->f_mapping->host;
- struct request_queue *q = lo->lo_queue;
- + struct request_queue *backingq;
- +
- + /*
- + * If the backing device is a block device, mirror its zeroing
- + * capability. REQ_OP_DISCARD translates to a zero-out even when backed
- + * by block devices to keep consistent behavior with file-backed loop
- + * devices.
- + */
- + if (S_ISBLK(inode->i_mode) && !lo->lo_encrypt_key_size) {
- + 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
- @@ -870,22 +886,24 @@ static void loop_config_discard(struct l
- * 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)
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