[PATCH v2] mac80211: Fix clang warning about constant operand in logical operation

[PATCH v2] mac80211: Fix clang warning about constant operand in logical operation

[Matthias Kaehlcke]

When clang detects a non-boolean constant in a logical operation it
generates a 'constant-logical-operand' warning. In
ieee80211_try_rate_control_ops_get() the result of strlen(<const str>)
is used in a logical operation, clang resolves the expression to an
(integer) constant at compile time when clang's builtin strlen function
is used.

Change the condition to check for strlen() > 0 to make the constant
operand boolean and thus avoid the warning.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
Changes in v2:
- Changed expression to strlen() > 0 to make constant operand boolean
  instead of splitting up condition
- Updated commit message

 net/mac80211/rate.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/rate.c b/net/mac80211/rate.c
index 206698bc93f4..694faf6ab574 100644
--- a/net/mac80211/rate.c
+++ b/net/mac80211/rate.c
@@ -173,9 +173,11 @@ ieee80211_rate_control_ops_get(const char *name)
 		/* try default if specific alg requested but not found */
 		ops = ieee80211_try_rate_control_ops_get(ieee80211_default_rc_algo);
 
-	/* try built-in one if specific alg requested but not found */
-	if (!ops && strlen(CONFIG_MAC80211_RC_DEFAULT))
+	/* Note: check for > 0 is intentional to avoid clang warning */
+	if (!ops && (strlen(CONFIG_MAC80211_RC_DEFAULT) > 0))
+		/* try built-in one if specific alg requested but not found */
 		ops = ieee80211_try_rate_control_ops_get(CONFIG_MAC80211_RC_DEFAULT);
+
 	kernel_param_unlock(THIS_MODULE);
 
 	return ops;
-- 
2.12.2.715.g7642488e1d-goog

Re: [PATCH v2] mac80211: Fix clang warning about constant operand in logical operation

[Johannes Berg]

On Thu, 2017-04-06 at 16:31 -0700, Matthias Kaehlcke wrote:
> When clang detects a non-boolean constant in a logical operation it
> generates a 'constant-logical-operand' warning. In
> ieee80211_try_rate_control_ops_get() the result of strlen(<const
> str>)
> is used in a logical operation, clang resolves the expression to an
> (integer) constant at compile time when clang's builtin strlen
> function
> is used.
> 
> Change the condition to check for strlen() > 0 to make the constant
> operand boolean and thus avoid the warning.
> 
Applied.

johannes