linux-kernel - [PATCH] loop: Fix missing discard support when using LOOP

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Message-Id: <20210617221158.7045-1-kristian@klausen.dk>
Date:   Fri, 18 Jun 2021 00:11:57 +0200
From:   Kristian Klausen <kristian@...usen.dk>
To:     linux-block@...r.kernel.org
Cc:     Kristian Klausen <kristian@...usen.dk>, stable@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Martijn Coenen <maco@...roid.com>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] loop: Fix missing discard support when using LOOP_CONFIGURE

Cc: <stable@...r.kernel.org> # 5.8.x-
Fixes: 3448914e8cc5 ("loop: Add LOOP_CONFIGURE ioctl")
Signed-off-by: Kristian Klausen <kristian@...usen.dk>
---
Tested like so (without the patch):
losetup 2.37<= uses LOOP_CONFIGURE instead of LOOP_SET_STATUS64[1]

# fallocate -l100M disk.img
# rmmod loop
# losetup --version
losetup from util-linux 2.36.2
# losetup --find --show disk.img
/dev/loop0
# grep '' /sys/devices/virtual/block/loop0/queue/*discard*
/sys/devices/virtual/block/loop0/queue/discard_granularity:4096
/sys/devices/virtual/block/loop0/queue/discard_max_bytes:4294966784
/sys/devices/virtual/block/loop0/queue/discard_max_hw_bytes:4294966784
/sys/devices/virtual/block/loop0/queue/discard_zeroes_data:0
/sys/devices/virtual/block/loop0/queue/max_discard_segments:1
# losetup -d /dev/loop0
# [update util-linux]
# losetup --version
losetup from util-linux 2.37
# rmmod loop
# losetup --find --show disk.img
/dev/loop0
# grep '' /sys/devices/virtual/block/loop0/queue/*discard*
/sys/devices/virtual/block/loop0/queue/discard_granularity:0
/sys/devices/virtual/block/loop0/queue/discard_max_bytes:0
/sys/devices/virtual/block/loop0/queue/discard_max_hw_bytes:0
/sys/devices/virtual/block/loop0/queue/discard_zeroes_data:0
/sys/devices/virtual/block/loop0/queue/max_discard_segments:1


With the patch applied:

# losetup --version
losetup from util-linux 2.37
# rmmod loop
# losetup --find --show disk.img
/dev/loop0
# grep '' /sys/devices/virtual/block/loop0/queue/*discard*
/sys/devices/virtual/block/loop0/queue/discard_granularity:4096
/sys/devices/virtual/block/loop0/queue/discard_max_bytes:4294966784
/sys/devices/virtual/block/loop0/queue/discard_max_hw_bytes:4294966784
/sys/devices/virtual/block/loop0/queue/discard_zeroes_data:0
/sys/devices/virtual/block/loop0/queue/max_discard_segments:1

[1] https://github.com/karelzak/util-linux/pull/1152

 drivers/block/loop.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 76e12f3482a9..ec957f6d8a49 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1168,6 +1168,8 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 	if (partscan)
 		lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
 
+	loop_config_discard(lo);
+
 	/* Grab the block_device to prevent its destruction after we
 	 * put /dev/loopXX inode. Later in __loop_clr_fd() we bdput(bdev).
 	 */

base-commit: 70585216fe7730d9fb5453d3e2804e149d0fe201
-- 
2.32.0