From 9a4c8019471386c6fb039ae9e30f5216b6b55a9e Mon Sep 17 00:00:00 2001
From: Carlos Maiolino <cmaiolino@redhat.com>
Date: Mon, 10 Dec 2012 16:30:45 -0500
Subject: ext4: ensure Inode flags consistency are checked at build time
Flags being used by atomic operations in inode flags (e.g.
ext4_test_inode_flag(), should be consistent with that actually stored
in inodes, i.e.: EXT4_XXX_FL.
It ensures that this consistency is checked at build-time, not at
run-time.
Currently, the flags consistency are being checked at run-time, but,
there is no real reason to not do a build-time check instead of a
run-time check. The code is comparing macro defined values with enum
type variables, where both are constants, so, there is no problem in
comparing constants at build-time.
enum variables are treated as constants by the C compiler, according
to the C99 specs (see www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf
sec. 6.2.5, item 16), so, there is no real problem in comparing an
enumeration type at build time
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
fs/ext4/ext4.h | 29 +++++++++++++----------------
fs/ext4/super.c | 1 +
2 files changed, 14 insertions(+), 16 deletions(-)
(limited to 'fs')
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index e20dc38858d4..b79d613091d0 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -463,25 +463,22 @@ enum {
EXT4_INODE_RESERVED = 31, /* reserved for ext4 lib */
};
-#define TEST_FLAG_VALUE(FLAG) (EXT4_##FLAG##_FL == (1 << EXT4_INODE_##FLAG))
-#define CHECK_FLAG_VALUE(FLAG) if (!TEST_FLAG_VALUE(FLAG)) { \
- printk(KERN_EMERG "EXT4 flag fail: " #FLAG ": %d %d\n", \
- EXT4_##FLAG##_FL, EXT4_INODE_##FLAG); BUG_ON(1); }
-
-/*
- * Since it's pretty easy to mix up bit numbers and hex values, and we
- * can't do a compile-time test for ENUM values, we use a run-time
- * test to make sure that EXT4_XXX_FL is consistent with respect to
- * EXT4_INODE_XXX. If all is well the printk and BUG_ON will all drop
- * out so it won't cost any extra space in the compiled kernel image.
- * But it's important that these values are the same, since we are
- * using EXT4_INODE_XXX to test for the flag values, but EXT4_XX_FL
- * must be consistent with the values of FS_XXX_FL defined in
- * include/linux/fs.h and the on-disk values found in ext2, ext3, and
- * ext4 filesystems, and of course the values defined in e2fsprogs.
+/*
+ * Since it's pretty easy to mix up bit numbers and hex values, we use a
+ * build-time check to make sure that EXT4_XXX_FL is consistent with respect to
+ * EXT4_INODE_XXX. If all is well, the macros will be dropped, so, it won't cost
+ * any extra space in the compiled kernel image, otherwise, the build will fail.
+ * It's important that these values are the same, since we are using
+ * EXT4_INODE_XXX to test for flag values, but EXT4_XXX_FL must be consistent
+ * with the values of FS_XXX_FL defined in include/linux/fs.h and the on-disk
+ * values found in ext2, ext3 and ext4 filesystems, and of course the values
+ * defined in e2fsprogs.
*
* It's not paranoia if the Murphy's Law really *is* out to get you. :-)
*/
+#define TEST_FLAG_VALUE(FLAG) (EXT4_##FLAG##_FL == (1 << EXT4_INODE_##FLAG))
+#define CHECK_FLAG_VALUE(FLAG) BUILD_BUG_ON(!TEST_FLAG_VALUE(FLAG))
+
static inline void ext4_check_flag_values(void)
{
CHECK_FLAG_VALUE(SECRM);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7d53adff8bd3..3cdb0a2fc648 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5278,6 +5278,7 @@ static int __init ext4_init_fs(void)
ext4_li_info = NULL;
mutex_init(&ext4_li_mtx);
+ /* Build-time check for flags consistency */
ext4_check_flag_values();
for (i = 0; i < EXT4_WQ_HASH_SZ; i++) {
--
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