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

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Message-ID: <YMvUw3E51fvezQN/@T590>
Date:   Fri, 18 Jun 2021 07:03:31 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Kristian Klausen <kristian@...usen.dk>
Cc:     linux-block@...r.kernel.org, stable@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Martijn Coenen <maco@...roid.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] loop: Fix missing discard support when using
 LOOP_CONFIGURE

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

Commit log?

> 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);
> +

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.

Otherwise, this patch looks fine.


Thanks,
Ming