To reduce unnecessary RMW cycles, permit partial pointers (offset, length)

to a hash-indexed binary buffer.

2 files changed, 36 insertions, 36 deletions

diff --git a/dbfs-backend.c b/dbfs-backend.c
index 4310a04..a75670a 100644
--- a/dbfs-backend.c
+++ b/dbfs-backend.c
@@ -23,12 +23,6 @@ struct dbfs_dirscan_info {
 	void			*end_ent;
 };
 
-struct dbfs_ext_list {
-	dbfs_blk_id_t		id;		/* block id */
-	guint64			off;		/* offset into block */
-	guint64			len;		/* length of fragment */
-};
-
 int dbmeta_del(const char *key_str)
 {
 	DBT key;
@@ -598,11 +592,12 @@ static void ext_list_free(GList *ext_list)
 	g_list_free(ext_list);
 }
 
-static int dbfs_ext_match(struct dbfs_inode *ino, guint64 off, guint64 rd_size,
+static int dbfs_ext_match(struct dbfs_inode *ino, guint64 off, guint32 rd_size,
 			  GList **ext_list_out)
 {
-	struct dbfs_ext_list *el;
-	guint64 pos, size, ext_list_want, bytes = 0;
+	struct dbfs_extent *ext;
+	guint64 pos;
+	guint32 ext_len, ext_off, ext_list_want, bytes = 0;
 	GList *ext_list = *ext_list_out;
 	gboolean in_frag;
 	unsigned int i;
@@ -612,47 +607,51 @@ static int dbfs_ext_match(struct dbfs_inode *ino, guint64 off, guint64 rd_size,
 	in_frag = FALSE;
 	ext_list_want = rd_size;
 	for (i = 0; i < ino->n_extents; i++) {
-		size = GUINT64_FROM_LE(ino->raw_inode->blocks[i].size);
+		ext_len = GUINT32_FROM_LE(ino->raw_inode->blocks[i].len);
+		ext_off = GUINT32_FROM_LE(ino->raw_inode->blocks[i].off);
+
+		if ((!in_frag) && ((pos + ext_len) > off)) {
+			guint32 skip;
 
-		if ((!in_frag) && ((pos + size) > off)) {
-			el = g_new(struct dbfs_ext_list, 1);
-			if (!el) {
+			ext = g_new(struct dbfs_extent, 1);
+			if (!ext) {
 				rc = -ENOMEM;
 				goto err_out;
 			}
 
-			memcpy(&el->id, &ino->raw_inode->blocks[i].id,
+			memcpy(&ext->id, &ino->raw_inode->blocks[i].id,
 			       sizeof(dbfs_blk_id_t));
-			el->off = off - pos;
-			el->len = MIN(size - el->off, ext_list_want);
+			skip = off - pos;
+			ext->off = skip + ext_off;
+			ext->len = MIN(ext_len - skip, ext_list_want);
 
-			ext_list = g_list_append(ext_list, el);
-			ext_list_want -= el->len;
-			bytes += el->len;
+			ext_list = g_list_append(ext_list, ext);
+			ext_list_want -= ext->len;
+			bytes += ext->len;
 			in_frag = TRUE;
 		}
 
 		else if (in_frag) {
-			el = g_new(struct dbfs_ext_list, 1);
-			if (!el) {
+			ext = g_new(struct dbfs_extent, 1);
+			if (!ext) {
 				rc = -ENOMEM;
 				goto err_out;
 			}
 
-			memcpy(&el->id, &ino->raw_inode->blocks[i].id,
+			memcpy(&ext->id, &ino->raw_inode->blocks[i].id,
 			       sizeof(dbfs_blk_id_t));
-			el->off = 0;
-			el->len = MIN(size, ext_list_want);
+			ext->off = ext_off;
+			ext->len = MIN(ext_len, ext_list_want);
 
-			ext_list = g_list_append(ext_list, el);
-			ext_list_want -= el->len;
-			bytes += el->len;
+			ext_list = g_list_append(ext_list, ext);
+			ext_list_want -= ext->len;
+			bytes += ext->len;
 
 			if (ext_list_want == 0)
 				break;
 		}
 
-		pos += size;
+		pos += ext_len;
 	}
 
 	*ext_list_out = ext_list;
@@ -714,18 +713,18 @@ int dbfs_read(guint64 ino_n, guint64 off, size_t read_req_size,
 
 	tmp = ext_list;
 	while (tmp) {
-		struct dbfs_ext_list *el;
+		struct dbfs_extent *ext;
 		void *frag;
 		size_t fraglen;
 
-		el = tmp->data;
-		rc = dbfs_ext_read(&el->id, &frag, &fraglen);
+		ext = tmp->data;
+		rc = dbfs_ext_read(&ext->id, &frag, &fraglen);
 		if (rc) {
 			free(buf);
 			buf = NULL;
 			goto out_list;
 		}
-		if ((el->off + el->len) > fraglen) {
+		if ((ext->off + ext->len) > fraglen) {
 			free(frag);
 			free(buf);
 			buf = NULL;
@@ -733,10 +732,10 @@ int dbfs_read(guint64 ino_n, guint64 off, size_t read_req_size,
 			goto out_list;
 		}
 
-		memcpy(buf + pos, frag + el->off, el->len);
+		memcpy(buf + pos, frag + ext->off, ext->len);
 		free(frag);
 
-		pos += el->len;
+		pos += ext->len;
 
 		tmp = tmp->next;
 	}
diff --git a/dbfs.h b/dbfs.h
index 3f2c8b2..02b002c 100644
--- a/dbfs.h
+++ b/dbfs.h
@@ -62,8 +62,9 @@ struct dbfs_xlist {
 } __attribute__ ((packed));
 
 struct dbfs_extent {
-	dbfs_blk_id_t	id;
-	guint64		size;
+	guint32			off;		/* offset into block */
+	guint32			len;		/* length of fragment */
+	dbfs_blk_id_t		id;		/* block id */
 } __attribute__ ((packed));
 
 struct dbfs_raw_inode {