linux-kernel - Re: [PATCH] jffs2: Hook up splice

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Date:   Tue, 30 Mar 2021 18:17:15 +0200
From:   Christoph Hellwig <hch@....de>
To:     Joel Stanley <joel@....id.au>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Richard Weinberger <richard@....at>,
        Al Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Christoph Hellwig <hch@....de>,
        "William A . Kennington III" <wak@...gle.com>,
        Lei YU <mine260309@...il.com>, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] jffs2: Hook up splice_write callback

On Wed, Mar 31, 2021 at 12:15:37AM +1030, Joel Stanley wrote:
> overlayfs using jffs2 as the upper filesystem would fail in some cases
> since moving to v5.10. The test case used was to run 'touch' on a file
> that exists in the lower fs, causing the modification time to be
> updated. It returns EINVAL when the bug is triggered.
> 
> A bisection showed this was introduced in v5.9-rc1, with commit
> 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops").
> Reverting that commit restores the expected behaviour.
> 
> Some digging showed that this was due to jffs2 lacking an implementation
> of splice_write. (For unknown reasons the warn_unsupported that should
> trigger was not displaying any output).
> 
> Adding this patch resolved the issue and the test now passes.

Looks good:

Reviewed-by: Christoph Hellwig <hch@....de>