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From:   Luis Henriques <lhenriques@suse.de>
To:     Alexander Viro <viro@zeniv.linux.org.uk>
Cc:     Nicolas Boichat <drinkcat@chromium.org>,
        Amir Goldstein <amir73il@gmail.com>,
        Olga Kornievskaia <aglo@umich.edu>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        0day robot <lkp@intel.com>,
        kernel test robot <oliver.sang@intel.com>,
        Luis Henriques <lhenriques@suse.de>
Subject: [PATCH] vfs: fix early copy_file_range return when len is zero
Date:   Tue, 18 May 2021 12:10:55 +0100
Message-Id: <20210518111055.16079-1-lhenriques@suse.de>
In-Reply-To: <877dk1zibo.fsf@suse.de>
References: <877dk1zibo.fsf@suse.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The early return from copy_file_range when len is zero should check if the
filesystem really implements this syscall, returning -EOPNOTSUPP if it doesn't,
and 0 otherwise.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Luis Henriques <lhenriques@suse.de>
---
Hi!

Since I got not feedback, I'm sending a patch that should fix this issue
reported by 0day.  Probably this should simply be squashed into v9, I can
send v10 if you prefer that.

Cheers,
--
Luis

 fs/read_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 9db7adf160d2..24b4bf704765 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1498,7 +1498,7 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 		return ret;
 
 	if (len == 0)
-		return 0;
+		return file_out->f_op->copy_file_range ? 0 : -EOPNOTSUPP;
 
 	file_start_write(file_out);