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

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Date:   Wed, 31 Mar 2021 00:15:37 +1030
From:   Joel Stanley <joel@....id.au>
To:     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>
Cc:     "William A . Kennington III" <wak@...gle.com>,
        Lei YU <mine260309@...il.com>, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] jffs2: Hook up splice_write callback

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.

Fixes: 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops")
Signed-off-by: Joel Stanley <joel@....id.au>
---
 fs/jffs2/file.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/jffs2/file.c b/fs/jffs2/file.c
index f8fb89b10227..4fc8cd698d1a 100644
--- a/fs/jffs2/file.c
+++ b/fs/jffs2/file.c
@@ -57,6 +57,7 @@ const struct file_operations jffs2_file_operations =
 	.mmap =		generic_file_readonly_mmap,
 	.fsync =	jffs2_fsync,
 	.splice_read =	generic_file_splice_read,
+	.splice_write = iter_file_splice_write,
 };

 /* jffs2_file_inode_operations */
-- 
2.30.2