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

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Message-ID: <a44566d9-4fef-43cc-b53e-bd102724344a@suse.com>
Date: Thu, 30 Oct 2025 17:23:32 +1030
From: Qu Wenruo <wqu@...e.com>
To: Christoph Hellwig <hch@....de>, Qu Wenruo <quwenruo.btrfs@....com>
Cc: "Darrick J. Wong" <djwong@...nel.org>, 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, linux-btrfs@...r.kernel.org
Subject: Re: [PATCH 4/4] xfs: fallback to buffered I/O for direct I/O when
 stable writes are required

在 2025/10/30 17:19, Christoph Hellwig 写道:
> On Thu, Oct 30, 2025 at 05:07:44PM +1030, Qu Wenruo wrote:
>> I mean some open flag like O_DIRECT_NO_FALLBACK, then we can directly
>> reutrn -ENOBLK without falling back to buffered IO (and no need to bother
>> the warning of falling back).
>>
>> This will provide the most accurate, true zero-copy for those programs that
>> really require zero-copy.
>>
>> And we won't need to bother falling back to buffered IO, it will be
>> something for the user space to bother.
> 
> So what is your application going to do if the open fails?

If it can not accept buffered fallback, error out.

If it can, do regular open without direct IO flags, and may be even open 
a bug report to the project, questioning if they really need direct IO 
in the first place.

Thanks,
Qu

> 
>>
>> Thanks,
>> Qu
> ---end quoted text---