Commit 9a4c8019 authored by Carlos Maiolino's avatar Carlos Maiolino Committed by Theodore Ts'o
Browse files

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: default avatarCarlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: default avatar"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++) {

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