JFFS2: Speed up and fix comparison functions

Copying complete nodes from flash can be slow if the flash is slow
to read. By only reading the data needed, the sorting operation can
be made much faster.

The directory entry comparison function also had a two bugs. First, it
did not ensure the name was copied, so the name comparison may have
been faulty (although it would have worked with NOR flash).  Second,
setting the ino to zero to ignore the entry did not work, since this
was either writing to a temporary buffer, or (for NOR flash) directly
to flash. Either way, the change was not remembered.

Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>

fs/jffs2/jffs2_1pass.c

@@ -598,14 +598,18 @@ insert_node(struct b_list *list, u32 offset)
  */
 static int compare_inodes(struct b_node *new, struct b_node *old)
 {
-	struct jffs2_raw_inode ojNew;
-	struct jffs2_raw_inode ojOld;
-	struct jffs2_raw_inode *jNew =
-		(struct jffs2_raw_inode *)get_fl_mem(new->offset, sizeof(ojNew), &ojNew);
-	struct jffs2_raw_inode *jOld =
-		(struct jffs2_raw_inode *)get_fl_mem(old->offset, sizeof(ojOld), &ojOld);
-
-	return jNew->version > jOld->version;
+	/*
+	 * Only read in the version info from flash, not the entire inode.
+	 * This can make a big difference to speed if flash is slow.
+	 */
+	u32 new_version;
+	u32 old_version;
+	get_fl_mem(new->offset + offsetof(struct jffs2_raw_inode, version),
+		   sizeof(new_version), &new_version);
+	get_fl_mem(old->offset + offsetof(struct jffs2_raw_inode, version),
+		   sizeof(old_version), &old_version);
+
+	return new_version > old_version;
 }
 
 /* Sort directory entries so all entries in the same directory
@@ -615,42 +619,45 @@ static int compare_inodes(struct b_node *new, struct b_node *old)
  */
 static int compare_dirents(struct b_node *new, struct b_node *old)
 {
-	struct jffs2_raw_dirent ojNew;
-	struct jffs2_raw_dirent ojOld;
-	struct jffs2_raw_dirent *jNew =
-		(struct jffs2_raw_dirent *)get_fl_mem(new->offset, sizeof(ojNew), &ojNew);
-	struct jffs2_raw_dirent *jOld =
-		(struct jffs2_raw_dirent *)get_fl_mem(old->offset, sizeof(ojOld), &ojOld);
-	int cmp;
-
-	/* ascending sort by pino */
-	if (jNew->pino != jOld->pino)
-		return jNew->pino > jOld->pino;
-
-	/* pino is the same, so use ascending sort by nsize, so
-	 * we don't do strncmp unless we really must.
-	 */
-	if (jNew->nsize != jOld->nsize)
-		return jNew->nsize > jOld->nsize;
-
-	/* length is also the same, so use ascending sort by name
-	 */
-	cmp = strncmp((char *)jNew->name, (char *)jOld->name, jNew->nsize);
-	if (cmp != 0)
-		return cmp > 0;
-
-	/* we have duplicate names in this directory, so use ascending
-	 * sort by version
+	/*
+	 * Using NULL as the buffer for NOR flash prevents the entire node
+	 * being read. This makes most comparisons much quicker as only one
+	 * or two entries from the node will be used most of the time.
 	 */
-	if (jNew->version > jOld->version) {
-		/* since jNew is newer, we know jOld is not valid, so
-		 * mark it with inode 0 and it will not be used
+	struct jffs2_raw_dirent *jNew = get_node_mem(new->offset, NULL);
+	struct jffs2_raw_dirent *jOld = get_node_mem(old->offset, NULL);
+	int cmp;
+	int ret;
+
+	if (jNew->pino != jOld->pino) {
+		/* ascending sort by pino */
+		ret = jNew->pino > jOld->pino;
+	} else if (jNew->nsize != jOld->nsize) {
+		/*
+		 * pino is the same, so use ascending sort by nsize,
+		 * so we don't do strncmp unless we really must.
 		 */
-		jOld->ino = 0;
-		return 1;
+		ret = jNew->nsize > jOld->nsize;
+	} else {
+		/*
+		 * length is also the same, so use ascending sort by name
+		 */
+		cmp = strncmp((char *)jNew->name, (char *)jOld->name,
+			jNew->nsize);
+		if (cmp != 0) {
+			ret = cmp > 0;
+		} else {
+			/*
+			 * we have duplicate names in this directory,
+			 * so use ascending sort by version
+			 */
+			ret = jNew->version > jOld->version;
+		}
 	}
+	put_fl_mem(jNew, NULL);
+	put_fl_mem(jOld, NULL);
 
-	return 0;
+	return ret;
 }
 #endif