linux-kernel - Re: [PATCH v3 3/3] xfs: reject max_atomic

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Message-ID: <331e38eb-e8b3-4ae4-9c74-81c79d6ce3a7@oracle.com>
Date: Fri, 25 Jul 2025 09:39:42 +0100
From: John Garry <john.g.garry@...cle.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: hch@....de, cem@...nel.org, dan.j.williams@...el.com, willy@...radead.org,
        jack@...e.cz, brauner@...nel.org, viro@...iv.linux.org.uk,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] xfs: reject max_atomic_write mount option for no
 reflink

On 24/07/2025 17:32, Darrick J. Wong wrote:
> On Thu, Jul 24, 2025 at 08:12:15AM +0000, John Garry wrote:
>> If the FS has no reflink, then atomic writes greater than 1x block are not
>> supported. As such, for no reflink it is pointless to accept setting
>> max_atomic_write when it cannot be supported, so reject max_atomic_write
>> mount option in this case.
>>
>> It could be still possible to accept max_atomic_write option of size 1x
>> block if HW atomics are supported, so check for this specifically.
>>
>> Fixes: 4528b9052731 ("xfs: allow sysadmins to specify a maximum atomic write limit at mount time")
>> Signed-off-by: John Garry<john.g.garry@...cle.com>
> /me wonders if "mkfs: allow users to configure the desired maximum
> atomic write size" needs a similar filter?
> 

Yeah, probably. But I am wondering if we should always require reflink 
for setting that max atomic mkfs option, and not have a special case of 
HW atomics available for 1x blocksize atomic writes.

> Reviewed-by: "Darrick J. Wong"<djwong@...nel.org>

cheers