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libext2fs: optimize ext2fs_bg_has_super() 

Reduce the CPU time needed when checking whether a block group has a
sparse superblock.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
debian-1.42.9
Theodore Ts'o 2013-06-15 18:29:52 -04:00
parent 3ac420165c
commit 4718395120
2 changed files with 11 additions and 10 deletions
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19
lib/ext2fs/closefs.c
View File

@ -20,12 +20,12 @@
#include "ext2_fs.h" #include "ext2_fs.h"
#include "ext2fsP.h" #include "ext2fsP.h"
static int test_root(int a, int b) static int test_root(unsigned int a, unsigned int b)
{ {
if (a == 0)
return 1;
while (1) { while (1) {
if (a == 1) if (a < b)
return 0;
if (a == b)
return 1; return 1;
if (a % b) if (a % b)
return 0; return 0;
@ -33,14 +33,15 @@ static int test_root(int a, int b)
} }
} }
int ext2fs_bg_has_super(ext2_filsys fs, int group_block) int ext2fs_bg_has_super(ext2_filsys fs, dgrp_t group)
{ {
if (!(fs->super->s_feature_ro_compat & if (!(fs->super->s_feature_ro_compat &
EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)) EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER) || group <= 1)
return 1; return 1;
if (!(group & 1))
if (test_root(group_block, 3) || (test_root(group_block, 5)) || return 0;
test_root(group_block, 7)) if (test_root(group, 3) || (test_root(group, 5)) ||
test_root(group, 7))
return 1; return 1;
return 0; return 0;

2
lib/ext2fs/ext2fs.h
View File

@ -911,7 +911,7 @@ extern errcode_t ext2fs_close(ext2_filsys fs);
extern errcode_t ext2fs_close2(ext2_filsys fs, int flags); extern errcode_t ext2fs_close2(ext2_filsys fs, int flags);
extern errcode_t ext2fs_flush(ext2_filsys fs); extern errcode_t ext2fs_flush(ext2_filsys fs);
extern errcode_t ext2fs_flush2(ext2_filsys fs, int flags); extern errcode_t ext2fs_flush2(ext2_filsys fs, int flags);
extern int ext2fs_bg_has_super(ext2_filsys fs, int group_block); extern int ext2fs_bg_has_super(ext2_filsys fs, dgrp_t group_block);
extern errcode_t ext2fs_super_and_bgd_loc2(ext2_filsys fs, extern errcode_t ext2fs_super_and_bgd_loc2(ext2_filsys fs,
dgrp_t group, dgrp_t group,
blk64_t *ret_super_blk, blk64_t *ret_super_blk,