Commit 06582bc8 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

block: loop:use kstatfs.f_bsize of backing file to set discard granularity 



If backing file's filesystem has implemented ->fallocate(), we think the
loop device can support discard, then pass sb->s_blocksize as
discard_granularity. However, some underlying FS, such as overlayfs,
doesn't set sb->s_blocksize, and causes discard_granularity to be set as
zero, then the warning in __blkdev_issue_discard() is triggered.

Christoph suggested to pass kstatfs.f_bsize as discard granularity, and
this way is fine because kstatfs.f_bsize means 'Optimal transfer block
size', which still matches with definition of discard granularity.

So fix the issue by setting discard_granularity as kstatfs.f_bsize if it
is available, otherwise claims discard isn't supported.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Reported-by: default avatarPei Zhang <pezhang@redhat.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220126035830.296465-1-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent a12821d5

drivers/block/loop.c

+7 −1
Original line number Diff line number Diff line
@@ -79,6 +79,7 @@ 
#include <linux/ioprio.h>

#include <linux/blk-cgroup.h>

#include <linux/sched/mm.h>

#include <linux/statfs.h>



#include "loop.h"
@@ -774,8 +775,13 @@ static void loop_config_discard(struct loop_device *lo) 
		granularity = 0;



	} else {

		struct kstatfs sbuf;



		max_discard_sectors = UINT_MAX >> 9;

		granularity = inode->i_sb->s_blocksize;

		if (!vfs_statfs(&file->f_path, &sbuf))

			granularity = sbuf.f_bsize;

		else

			max_discard_sectors = 0;

	}



	if (max_discard_sectors) {