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: <04db952d-2319-4ef9-8986-50e744b00b62@gmx.com>
Date: Thu, 30 Oct 2025 17:07:44 +1030
From: Qu Wenruo <quwenruo.btrfs@....com>
To: Christoph Hellwig <hch@....de>, Qu Wenruo <wqu@...e.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 16:28, Christoph Hellwig 写道:
[...]
>> It will be much straightforward if there is some flag allowing us to return
>> error directly if true zero-copy direct IO can not be executed.
> 
> I don't really understand this part.

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.

Thanks,
Qu