linux-kernel - Re: [PATCH v5 05/10] xfs: Iomap SW-based atomic write support

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Message-ID: <c9ebe7c7-69ea-44b9-872f-13755c59b9f3@oracle.com>
Date: Wed, 12 Mar 2025 16:11:02 +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 05/10] xfs: Iomap SW-based atomic write support

On 12/03/2025 15:55, Christoph Hellwig wrote:
>>> would make the core iomap code set REQ_ATOMIC on the bio for that
>>> iteration.
>> but we still need to tell ->iomap_begin about IOCB_ATOMIC, hence
> Yeah, ->iomap_begin  can't directly look at the iocb.
> 
>> IOMAP_DIO_BIO_ATOMIC which sets IOMAP_BIO_ATOMIC.
>> We can't allow __iomap_dio_rw() check IOCB_ATOMIC only (and set
>> IOMAP_BIO_ATOMIC), as this is the common path for COW and regular atomic
>> write
> Well, I'd imagine __iomap_dio_rw just sets IOMAP_ATOMIC from IOCB_ATOMIC
> and then it's up to file system internal state if it wants to set
> IOMAP_F_REQ_ATOMIC based on that, i.e. the actual setting of
> IOMAP_F_REQ_ATOMIC is fully controlled by the file system and not
> by the iomap core.

ok, fine. But I will also need to change ext4 to do the same (in terms 
of setting IOMAP_F_REQ_ATOMIC).

And I am thinking of IOMAP_F_ATOMIC_BIO as the name, as we mentioned 
earlier that it is not so nice to with clash block layer names

Thanks,
John