linux-kernel - Re: [PATCH v5 04/10] xfs: Reflink CoW-based atomic write support

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Message-ID: <ed2dcd4d-9d9c-496b-b28c-8540c301139b@oracle.com>
Date: Wed, 12 Mar 2025 14:48:56 +0000
From: John Garry <john.g.garry@...cle.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: brauner@...nel.org, djwong@...nel.org, cem@...nel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com,
        ritesh.list@...il.com, martin.petersen@...cle.com
Subject: Re: [PATCH v5 04/10] xfs: Reflink CoW-based atomic write support

On 12/03/2025 13:45, Christoph Hellwig wrote:
> On Wed, Mar 12, 2025 at 09:13:45AM +0000, John Garry wrote:
>>>> +	if (error || (!*shared && !atomic_sw))
>>>
>>> And it's pnly used once.  Basically is is used to force COW, right?
>>
>> Yes, we force it. Indeed, I think that is term you used a long time ago in
>> your RFC for atomic file updates.
>>
>> But that flag is being used to set XFS_BMAPI_EXTSZALIGN, so feels like a bit
>> of a disconnect as why we would set XFS_BMAPI_EXTSZALIGN for "forced cow". I
>> would need to spell that out.
> 
> Maybe use two flags for that even if they currently are set together?

ok, fine. Then it makes explaining why we set XFS_BMAPI_EXTSZALIGN for 
"force cow" a lot simpler in the code.

> Note that this would go away if we'd always align extsize hinted
> allocations, which I suspect is a good idea (even if I'm not 100% sure
> about it).
> 

Sure

Cheers,
John