linux-kernel - [PATCH 4.18 097/145] block, bfq: return nbytes and not zero from struct cftype .write() method

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Date:   Fri,  7 Sep 2018 23:09:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 4.18 097/145] block, bfq: return nbytes and not zero from struct cftype .write() method

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Maciej S. Szmigiero <mail@...iej.szmigiero.name>

commit fc8ebd01deeb12728c83381f6ec923e4a192ffd3 upstream.

The value that struct cftype .write() method returns is then directly
returned to userspace as the value returned by write() syscall, so it
should be the number of bytes actually written (or consumed) and not zero.

Returning zero from write() syscall makes programs like /bin/echo or bash
spin.

Signed-off-by: Maciej S. Szmigiero <mail@...iej.szmigiero.name>
Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
Cc: stable@...r.kernel.org
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/bfq-cgroup.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -913,7 +913,8 @@ static ssize_t bfq_io_set_weight(struct
 	if (ret)
 		return ret;

-	return bfq_io_set_weight_legacy(of_css(of), NULL, weight);
+	ret = bfq_io_set_weight_legacy(of_css(of), NULL, weight);
+	return ret ?: nbytes;
 }

 #ifdef CONFIG_DEBUG_BLK_CGROUP