linux-kernel - [PATCH] block: avoid -Wunused-but-set-parameter warning

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Date:   Tue, 23 Mar 2021 14:12:19 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Shaohua Li <shli@...com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Chaitanya Kulkarni <chaitanya.kulkarni@....com>,
        Hannes Reinecke <hare@...e.de>, Jan Kara <jack@...e.cz>,
        Damien Le Moal <damien.lemoal@....com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] block: avoid -Wunused-but-set-parameter warning

From: Arnd Bergmann <arnd@...db.de>

Building with 'make W=1' shows a warning for one function parameter
that is only set but not used in some configurations:

kernel/trace/blktrace.c: In function '__trace_note_message':
kernel/trace/blktrace.c:148:63: error: parameter 'blkcg' set but not used [-Werror=unused-but-set-parameter]
  148 | void __trace_note_message(struct blk_trace *bt, struct blkcg *blkcg,

Move the assignment into the #ifdef block that contains the only
use to clarify how it's used and avoid the warning.

Apparently this is the only -Wunused-but-set-parameter warning in the
kernel as of v5.12, after similar cleanups done by others. It may be time
to turn it on globally.

Fixes: 35fe6d763229 ("block: use standard blktrace API to output cgroup info for debug notes")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 kernel/trace/blktrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index c221e4c3f625..f9314351a7e2 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -170,9 +170,9 @@ void __trace_note_message(struct blk_trace *bt, struct blkcg *blkcg,
 	n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);
 	va_end(args);
 
+#ifdef CONFIG_BLK_CGROUP
 	if (!(blk_tracer_flags.val & TRACE_BLK_OPT_CGROUP))
 		blkcg = NULL;
-#ifdef CONFIG_BLK_CGROUP
 	trace_note(bt, current->pid, BLK_TN_MESSAGE, buf, n,
 		   blkcg ? cgroup_id(blkcg->css.cgroup) : 1);
 #else
-- 
2.29.2