Merge branch 'salted-string-hash'

This changes the vfs dentry hashing to mix in the parent pointer at the
_beginning_ of the hash, rather than at the end.

That actually improves both the hash and the code generation, because we
can move more of the computation to the "static" part of the dcache
setup, and do less at lookup runtime.

It turns out that a lot of other hash users also really wanted to mix in
a base pointer as a 'salt' for the hash, and so the slightly extended
interface ends up working well for other cases too.

Users that want a string hash that is purely about the string pass in a
'salt' pointer of NULL.

* merge branch 'salted-string-hash':
  fs/dcache.c: Save one 32-bit multiply in dcache lookup
  vfs: make the string hashes salt the hash

1 files changed, 25 insertions, 17 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 70580ab1445c..7cb9be3e200a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1890,9 +1890,9 @@ static inline unsigned int fold_hash(unsigned long x, unsigned long y)
  * payload bytes, to match the way that hash_name() iterates until it
  * finds the delimiter after the name.
  */
-unsigned int full_name_hash(const char *name, unsigned int len)
+unsigned int full_name_hash(const void *salt, const char *name, unsigned int len)
 {
-	unsigned long a, x = 0, y = 0;
+	unsigned long a, x = 0, y = (unsigned long)salt;
 
 	for (;;) {
 		if (!len)
@@ -1911,15 +1911,19 @@ done:
 EXPORT_SYMBOL(full_name_hash);
 
 /* Return the "hash_len" (hash and length) of a null-terminated string */
-u64 hashlen_string(const char *name)
+u64 hashlen_string(const void *salt, const char *name)
 {
-	unsigned long a = 0, x = 0, y = 0, adata, mask, len;
+	unsigned long a = 0, x = 0, y = (unsigned long)salt;
+	unsigned long adata, mask, len;
 	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
 
-	len = -sizeof(unsigned long);
+	len = 0;
+	goto inside;
+
 	do {
 		HASH_MIX(x, y, a);
 		len += sizeof(unsigned long);
+inside:
 		a = load_unaligned_zeropad(name+len);
 	} while (!has_zero(a, &adata, &constants));
 
@@ -1935,15 +1939,19 @@ EXPORT_SYMBOL(hashlen_string);
  * Calculate the length and hash of the path component, and
  * return the "hash_len" as the result.
  */
-static inline u64 hash_name(const char *name)
+static inline u64 hash_name(const void *salt, const char *name)
 {
-	unsigned long a = 0, b, x = 0, y = 0, adata, bdata, mask, len;
+	unsigned long a = 0, b, x = 0, y = (unsigned long)salt;
+	unsigned long adata, bdata, mask, len;
 	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
 
-	len = -sizeof(unsigned long);
+	len = 0;
+	goto inside;
+
 	do {
 		HASH_MIX(x, y, a);
 		len += sizeof(unsigned long);
+inside:
 		a = load_unaligned_zeropad(name+len);
 		b = a ^ REPEAT_BYTE('/');
 	} while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants)));
@@ -1959,9 +1967,9 @@ static inline u64 hash_name(const char *name)
 #else	/* !CONFIG_DCACHE_WORD_ACCESS: Slow, byte-at-a-time version */
 
 /* Return the hash of a string of known length */
-unsigned int full_name_hash(const char *name, unsigned int len)
+unsigned int full_name_hash(const void *salt, const char *name, unsigned int len)
 {
-	unsigned long hash = init_name_hash();
+	unsigned long hash = init_name_hash(salt);
 	while (len--)
 		hash = partial_name_hash((unsigned char)*name++, hash);
 	return end_name_hash(hash);
@@ -1969,9 +1977,9 @@ unsigned int full_name_hash(const char *name, unsigned int len)
 EXPORT_SYMBOL(full_name_hash);
 
 /* Return the "hash_len" (hash and length) of a null-terminated string */
-u64 hashlen_string(const char *name)
+u64 hashlen_string(const void *salt, const char *name)
 {
-	unsigned long hash = init_name_hash();
+	unsigned long hash = init_name_hash(salt);
 	unsigned long len = 0, c;
 
 	c = (unsigned char)*name;
@@ -1988,9 +1996,9 @@ EXPORT_SYMBOL(hashlen_string);
  * We know there's a real path component here of at least
  * one character.
  */
-static inline u64 hash_name(const char *name)
+static inline u64 hash_name(const void *salt, const char *name)
 {
-	unsigned long hash = init_name_hash();
+	unsigned long hash = init_name_hash(salt);
 	unsigned long len = 0, c;
 
 	c = (unsigned char)*name;
@@ -2030,7 +2038,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
 		if (err)
 			return err;
 
-		hash_len = hash_name(name);
+		hash_len = hash_name(nd->path.dentry, name);
 
 		type = LAST_NORM;
 		if (name[0] == '.') switch (hashlen_len(hash_len)) {
@@ -2436,7 +2444,7 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
 
 	this.name = name;
 	this.len = len;
-	this.hash = full_name_hash(name, len);
+	this.hash = full_name_hash(base, name, len);
 	if (!len)
 		return ERR_PTR(-EACCES);
 
@@ -2489,7 +2497,7 @@ struct dentry *lookup_one_len_unlocked(const char *name,
 
 	this.name = name;
 	this.len = len;
-	this.hash = full_name_hash(name, len);
+	this.hash = full_name_hash(base, name, len);
 	if (!len)
 		return ERR_PTR(-EACCES);