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tomoyo: improve hash bucket dispersion 

When examining the network device name hash, it was discovered that
the low order bits of full_name_hash() are not very well dispersed
across the possible values. When used by filesystem code, this is handled
by folding with the function hash_long().

The only other non-filesystem usage of full_name_hash() at this time
appears to be in TOMOYO. This patch should fix that.

I do not use TOMOYO at this time, so this patch is build tested only.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>
This commit is contained in:
Stephen Hemminger 2009-10-27 19:24:46 -07:00 committed by James Morris
parent d6ba452128
commit 024e1a4941
1 changed files with 9 additions and 4 deletions
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13
security/tomoyo/realpath.c
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@ -13,6 +13,8 @@
#include <linux/mount.h>
#include <linux/mnt_namespace.h>
#include <linux/fs_struct.h>
#include <linux/hash.h>
#include "common.h"
#include "realpath.h"
@ -263,7 +265,8 @@ static unsigned int tomoyo_quota_for_savename;
* table. Frequency of appending strings is very low. So we don't need
* large (e.g. 64k) hash size. 256 will be sufficient.
*/
#define TOMOYO_MAX_HASH 256
#define TOMOYO_HASH_BITS 8
#define TOMOYO_MAX_HASH (1u<<TOMOYO_HASH_BITS)
/*
* tomoyo_name_entry is a structure which is used for linking
@ -315,6 +318,7 @@ const struct tomoyo_path_info *tomoyo_save_name(const char *name)
struct tomoyo_free_memory_block_list *fmb;
int len;
char *cp;
struct list_head *head;
if (!name)
return NULL;
@ -325,9 +329,10 @@ const struct tomoyo_path_info *tomoyo_save_name(const char *name)
return NULL;
}
hash = full_name_hash((const unsigned char *) name, len - 1);
head = &tomoyo_name_list[hash_long(hash, TOMOYO_HASH_BITS)];
mutex_lock(&lock);
list_for_each_entry(ptr, &tomoyo_name_list[hash % TOMOYO_MAX_HASH],
list) {
list_for_each_entry(ptr, head, list) {
if (hash == ptr->entry.hash && !strcmp(name, ptr->entry.name))
goto out;
}
@ -365,7 +370,7 @@ const struct tomoyo_path_info *tomoyo_save_name(const char *name)
tomoyo_fill_path_info(&ptr->entry);
fmb->ptr += len;
fmb->len -= len;
list_add_tail(&ptr->list, &tomoyo_name_list[hash % TOMOYO_MAX_HASH]);
list_add_tail(&ptr->list, head);
if (fmb->len == 0) {
list_del(&fmb->list);
kfree(fmb);