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Commit 9a4c8019 authored Dec 10, 2012 by Carlos Maiolino Committed by Theodore Ts'o Dec 10, 2012

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>

parent 939da108

fs/ext4/ext4.h

+13 −16

Original line number	Diff line number	Diff line
		@@ -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);

fs/ext4/super.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -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++) {