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>

include/linux/stringhash.h

@@ -34,7 +34,7 @@
  */
 
 /* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
-#define init_name_hash()		0
+#define init_name_hash(salt)		(unsigned long)(salt)
 
 /* partial hash update function. Assume roughly 4 bits per character */
 static inline unsigned long
@@ -60,7 +60,7 @@ static inline unsigned long end_name_hash(unsigned long hash)
  *
  * If not set, this falls back to a wrapper around the preceding.
  */
-extern unsigned int __pure full_name_hash(const char *, unsigned int);
+extern unsigned int __pure full_name_hash(const void *salt, const char *, unsigned int);
 
 /*
  * A hash_len is a u64 with the hash of a string in the low
@@ -71,6 +71,6 @@ extern unsigned int __pure full_name_hash(const char *, unsigned int);
 #define hashlen_create(hash, len) ((u64)(len)<<32 | (u32)(hash))
 
 /* Return the "hash_len" (hash and length) of a null-terminated string */
-extern u64 __pure hashlen_string(const char *name);
+extern u64 __pure hashlen_string(const void *salt, const char *name);
 
 #endif	/* __LINUX_STRINGHASH_H */