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

5 files changed, 11 insertions, 7 deletions

diff --git a/fs/jffs2/dir.c b/fs/jffs2/dir.c
index 84c4bf3631a2..30eb33ff8189 100644
--- a/fs/jffs2/dir.c
+++ b/fs/jffs2/dir.c
@@ -81,6 +81,7 @@ static struct dentry *jffs2_lookup(struct inode *dir_i, struct dentry *target,
 	struct jffs2_full_dirent *fd = NULL, *fd_list;
 	uint32_t ino = 0;
 	struct inode *inode = NULL;
+	unsigned int nhash;
 
 	jffs2_dbg(1, "jffs2_lookup()\n");
 
@@ -89,11 +90,14 @@ static struct dentry *jffs2_lookup(struct inode *dir_i, struct dentry *target,
 
 	dir_f = JFFS2_INODE_INFO(dir_i);
 
+	/* The 'nhash' on the fd_list is not the same as the dentry hash */
+	nhash = full_name_hash(NULL, target->d_name.name, target->d_name.len);
+
 	mutex_lock(&dir_f->sem);
 
 	/* NB: The 2.2 backport will need to explicitly check for '.' and '..' here */
-	for (fd_list = dir_f->dents; fd_list && fd_list->nhash <= target->d_name.hash; fd_list = fd_list->next) {
-		if (fd_list->nhash == target->d_name.hash &&
+	for (fd_list = dir_f->dents; fd_list && fd_list->nhash <= nhash; fd_list = fd_list->next) {
+		if (fd_list->nhash == nhash &&
 		    (!fd || fd_list->version > fd->version) &&
 		    strlen(fd_list->name) == target->d_name.len &&
 		    !strncmp(fd_list->name, target->d_name.name, target->d_name.len)) {
diff --git a/fs/jffs2/readinode.c b/fs/jffs2/readinode.c
index bfebbf13698c..06a71dbd4833 100644
--- a/fs/jffs2/readinode.c
+++ b/fs/jffs2/readinode.c
@@ -674,7 +674,7 @@ static inline int read_direntry(struct jffs2_sb_info *c, struct jffs2_raw_node_r
 		}
 	}
 
-	fd->nhash = full_name_hash(fd->name, rd->nsize);
+	fd->nhash = full_name_hash(NULL, fd->name, rd->nsize);
 	fd->next = NULL;
 	fd->name[rd->nsize] = '\0';
 
diff --git a/fs/jffs2/scan.c b/fs/jffs2/scan.c
index 9ad5ba4b299b..90431dd613b8 100644
--- a/fs/jffs2/scan.c
+++ b/fs/jffs2/scan.c
@@ -1100,7 +1100,7 @@ static int jffs2_scan_dirent_node(struct jffs2_sb_info *c, struct jffs2_eraseblo
 	fd->next = NULL;
 	fd->version = je32_to_cpu(rd->version);
 	fd->ino = je32_to_cpu(rd->ino);
-	fd->nhash = full_name_hash(fd->name, checkedlen);
+	fd->nhash = full_name_hash(NULL, fd->name, checkedlen);
 	fd->type = rd->type;
 	jffs2_add_fd_to_list(c, fd, &ic->scan_dents);
 
diff --git a/fs/jffs2/summary.c b/fs/jffs2/summary.c
index bc5385471a6e..be7c8a6a5748 100644
--- a/fs/jffs2/summary.c
+++ b/fs/jffs2/summary.c
@@ -476,7 +476,7 @@ static int jffs2_sum_process_sum_data(struct jffs2_sb_info *c, struct jffs2_eras
 				fd->next = NULL;
 				fd->version = je32_to_cpu(spd->version);
 				fd->ino = je32_to_cpu(spd->ino);
-				fd->nhash = full_name_hash(fd->name, checkedlen);
+				fd->nhash = full_name_hash(NULL, fd->name, checkedlen);
 				fd->type = spd->type;
 
 				jffs2_add_fd_to_list(c, fd, &ic->scan_dents);
diff --git a/fs/jffs2/write.c b/fs/jffs2/write.c
index 7fb187ab2682..cda9a361368e 100644
--- a/fs/jffs2/write.c
+++ b/fs/jffs2/write.c
@@ -245,7 +245,7 @@ struct jffs2_full_dirent *jffs2_write_dirent(struct jffs2_sb_info *c, struct jff
 
 	fd->version = je32_to_cpu(rd->version);
 	fd->ino = je32_to_cpu(rd->ino);
-	fd->nhash = full_name_hash(name, namelen);
+	fd->nhash = full_name_hash(NULL, name, namelen);
 	fd->type = rd->type;
 	memcpy(fd->name, name, namelen);
 	fd->name[namelen]=0;
@@ -598,7 +598,7 @@ int jffs2_do_unlink(struct jffs2_sb_info *c, struct jffs2_inode_info *dir_f,
 		jffs2_add_fd_to_list(c, fd, &dir_f->dents);
 		mutex_unlock(&dir_f->sem);
 	} else {
-		uint32_t nhash = full_name_hash(name, namelen);
+		uint32_t nhash = full_name_hash(NULL, name, namelen);
 
 		fd = dir_f->dents;
 		/* We don't actually want to reserve any space, but we do