On 18.06.2021 01.03, Ming Lei wrote:

On Fri, Jun 18, 2021 at 12:11:57AM +0200, Kristian Klausen wrote:

Commit log?

I will try to come up with a commit message. AFAIU the missing call to 
loop_config_discard() causes the block device to report "no discard 
support" (best-case) or stale/incorrect discard support (ex: if the loop 
device was configured with LOOP_SET_STATUS(64) and later LOOP_CONFIGURE).

quoted

Cc: <redacted> # 5.8.x-
Fixes: 3448914e8cc5 ("loop: Add LOOP_CONFIGURE ioctl")
Signed-off-by: Kristian Klausen <redacted>
---
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);
+

It could be better to move loop_config_discard() around
loop_update_rotational/loop_update_dio(), then we setup everything
before updating loop as Lo_bound.

I will move it before loop_update_rotational().

Otherwise, this patch looks fine.


Thanks,
Ming