linux-kernel - [PATCH 3/5] virtio: Fix none-const BUILD_BUG

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Date:	Mon, 01 Sep 2008 16:13:38 +0300
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Ingo Molnar <mingo@...e.hu>, Rusty Russell <rusty@...tcorp.com.au>,
	"David S. Miller" <davem@...emloft.net>,
	Ivo van Doorn <IvDoorn@...il.com>,
	"John W. Linville" <linville@...driver.com>
CC:	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jan Beulich <jbeulich@...ell.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/5] virtio: Fix none-const BUILD_BUG_ON usage


BUILD_BUG_ON can not be used cross inline parametrization boundary.
I've put the BUILD_BUG_ON(_ZERO) in a macro outside of the inline
definition. (So it is in the caller scope).

NOTE to Rusty:
  If I remove the "__builtin_constant_p ?" part then code compiles
  just fine, because all call sights of virtio_has_feature() use
  constants for fbit. But it seems like it was not intended to be
  forced.

Signed-off-by: Boaz Harrosh <bharrosh@...asas.com>
CC: Ingo Molnar <mingo@...e.hu>
CC: Rusty Russell <rusty@...tcorp.com.au>
---
 include/linux/virtio_config.h |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index bf8ec28..d9402d8 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -92,17 +92,19 @@ void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
  * @vdev: the device
  * @fbit: the feature bit
  */
-static inline bool virtio_has_feature(const struct virtio_device *vdev,
+static inline bool __virtio_has_feature(const struct virtio_device *vdev,
 				      unsigned int fbit)
 {
-	/* Did you forget to fix assumptions on max features? */
-	if (__builtin_constant_p(fbit))
-		BUILD_BUG_ON(fbit >= 32);
-
 	virtio_check_driver_offered_feature(vdev, fbit);
 	return test_bit(fbit, vdev->features);
 }
 
+/* Did you forget to fix assumptions on max features? */
+#define virtio_has_feature(vdev, fbit) \
+	((__builtin_constant_p(fbit) ? BUILD_BUG_ON_ZERO(fbit >= 32) : 0) + \
+	__virtio_has_feature(vdev, fbit))
+	
+
 /**
  * virtio_config_val - look for a feature and get a virtio config entry.
  * @vdev: the virtio device
-- 
1.5.6.rc1.5.gadf6


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