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>

fs/isofs/inode.c

@@ -174,7 +174,7 @@ struct iso9660_options{
  * Compute the hash for the isofs name corresponding to the dentry.
  */
 static int
-isofs_hashi_common(struct qstr *qstr, int ms)
+isofs_hashi_common(const struct dentry *dentry, struct qstr *qstr, int ms)
 {
 	const char *name;
 	int len;
@@ -188,7 +188,7 @@ isofs_hashi_common(struct qstr *qstr, int ms)
 			len--;
 	}
 
-	hash = init_name_hash();
+	hash = init_name_hash(dentry);
 	while (len--) {
 		c = tolower(*name++);
 		hash = partial_name_hash(c, hash);
@@ -231,7 +231,7 @@ static int isofs_dentry_cmp_common(
 static int
 isofs_hashi(const struct dentry *dentry, struct qstr *qstr)
 {
-	return isofs_hashi_common(qstr, 0);
+	return isofs_hashi_common(dentry, qstr, 0);
 }
 
 static int
@@ -246,7 +246,7 @@ isofs_dentry_cmpi(const struct dentry *parent, const struct dentry *dentry,
  * Compute the hash for the isofs name corresponding to the dentry.
  */
 static int
-isofs_hash_common(struct qstr *qstr, int ms)
+isofs_hash_common(const struct dentry *dentry, struct qstr *qstr, int ms)
 {
 	const char *name;
 	int len;
@@ -258,7 +258,7 @@ isofs_hash_common(struct qstr *qstr, int ms)
 			len--;
 	}
 
-	qstr->hash = full_name_hash(name, len);
+	qstr->hash = full_name_hash(dentry, name, len);
 
 	return 0;
 }
@@ -266,13 +266,13 @@ isofs_hash_common(struct qstr *qstr, int ms)
 static int
 isofs_hash_ms(const struct dentry *dentry, struct qstr *qstr)
 {
-	return isofs_hash_common(qstr, 1);
+	return isofs_hash_common(dentry, qstr, 1);
 }
 
 static int
 isofs_hashi_ms(const struct dentry *dentry, struct qstr *qstr)
 {
-	return isofs_hashi_common(qstr, 1);
+	return isofs_hashi_common(dentry, qstr, 1);
 }
 
 static int