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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <c91c87ab-dd85-4c42-9af4-a25ea2540de3@gmail.com>
Date: Wed, 12 Nov 2025 12:43:05 +0530
From: "Nirjhar Roy (IBM)" <nirjhar.roy.lists@...il.com>
To: Christoph Hellwig <hch@....de>
Cc: Carlos Maiolino <cem@...nel.org>, Christian Brauner <brauner@...nel.org>,
 Jan Kara <jack@...e.cz>, "Martin K. Petersen" <martin.petersen@...cle.com>,
 linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-raid@...r.kernel.org,
 linux-block@...r.kernel.org
Subject: Re: [PATCH 4/4] xfs: fallback to buffered I/O for direct I/O when
 stable writes are required

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