linux-kernel - Re: [PATCH] loop: Disable fallocate() zero and discard if not supported

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Message-ID: <4726b305-0d26-42c6-aa25-820e662f3ea9@nvidia.com>
Date: Mon, 10 Jun 2024 02:47:28 +0000
From: Chaitanya Kulkarni <chaitanyak@...dia.com>
To: Cyril Hrubis <chrubis@...e.cz>
CC: Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@...radead.org>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Jan Kara
	<jack@...e.cz>
Subject: Re: [PATCH] loop: Disable fallocate() zero and discard if not
 supported

On 6/7/2024 10:42 PM, Christoph Hellwig wrote:
> On Fri, Jun 07, 2024 at 11:15:55AM +0200, Cyril Hrubis wrote:
>> If fallcate is implemented but zero and discard operations are not
>> supported by the filesystem the backing file is on we continue to fill
>> dmesg with errors from the blk_mq_end_request() since each time we call
>> fallocate() on the loop device the EOPNOTSUPP error from lo_fallocate()
>> ends up propagated into the block layer. In the end syscall succeeds
>> since the blkdev_issue_zeroout() falls back to writing zeroes which
>> makes the errors even more misleading and confusing.
>>
>> How to reproduce:
>>
>> 1. make sure /tmp is mounted as tmpfs
>> 2. dd if=/dev/zero of=/tmp/disk.img bs=1M count=100
>> 3. losetup /dev/loop0 /tmp/disk.img
>> 4. mkfs.ext2 /dev/loop0
>> 5. dmesg |tail
> Can you wire this up for blktests?

Please CC Shin'ichiro Kawasaki <shinichiro.kawasaki@....com> and me when
you do that ..

-ck