Re: [PATCH 4/4] xfs: fallback to buffered I/O for direct I/O when stable writes are required

Nirjhar Roy (IBM)
2025-11-12T07:14:10Z

On 11/10/25 19:29, Christoph Hellwig wrote:
> On Mon, Nov 10, 2025 at 07:08:05PM +0530, Nirjhar Roy (IBM) wrote:
>> Minor: Let us say that an user opens a file in O_DIRECT in an atomic
>> write enabled device(requiring stable writes), we get this warning
>> once. Now the same/different user/application opens another file
>> with O_DIRECT in the same atomic write enabled device and expects
>> atomic write to be enabled - but it will not be enabled (since the
>> kernel has falled back to the uncached buffered write path)
>> without any warning message. Won't that be a bit confusing for the
>> user (of course unless the user is totally aware of the kernel's exact
>> behavior)?
> The kernel with this patch should reject IOCB_ATOMIC writes because
> the FMODE_CAN_ATOMIC_WRITE is not set when we need to fallback.
Okay, makes sense.
>
> But anyway, based on the feedback in this thread I plan to revisit the
> approach so that the I/O issuer can declare I/O stable (initially just
> for buffered I/O, but things like nvmet and nfsd might be able to
> guarantee that for direct I/O as well), and then bounce buffer in lower
> layers. This should then also support parallel writes, async I/O and
> atomic writes.

Okay.

--NR

>
--
Nirjhar Roy
Linux Kernel Developer
IBM, Bangalore