From 9a4c8019471386c6fb039ae9e30f5216b6b55a9e Mon Sep 17 00:00:00 2001 From: Carlos Maiolino Date: Mon, 10 Dec 2012 16:30:45 -0500 Subject: [PATCH] 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 Signed-off-by: "Theodore Ts'o" --- fs/ext4/ext4.h | 29 +++++++++++++---------------- fs/ext4/super.c | 1 + 2 files changed, 14 insertions(+), 16 deletions(-) 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++) { -- 2.20.1