vfs: make the string hashes salt the hash

We always mixed in the parent pointer into the dentry name hash, but we
did it late at lookup time.  It turns out that we can simplify that
lookup-time action by salting the hash with the parent pointer early
instead of late.

A few other users of our string hashes also wanted to mix in their own
pointers into the hash, and those are updated to use the same mechanism.

Hash users that don't have any particular initial salt can just use the
NULL pointer as a no-salt.

Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: George Spelvin <linux@sciencehorizons.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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);