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: <20251030064917.GA13549@lst.de>
Date: Thu, 30 Oct 2025 07:49:17 +0100
From: Christoph Hellwig <hch@....de>
To: Qu Wenruo <quwenruo.btrfs@....com>
Cc: Christoph Hellwig <hch@....de>, Qu Wenruo <wqu@...e.com>,
	"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

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?

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