zfs: make less syscalls

1 files changed, 58 insertions, 37 deletions

diff --git a/libblkid/src/superblocks/zfs.c b/libblkid/src/superblocks/zfs.c
index 4a64a03de5..9b5601e0ab 100644
--- a/libblkid/src/superblocks/zfs.c
+++ b/libblkid/src/superblocks/zfs.c
@@ -20,6 +20,7 @@
 #define VDEV_LABEL_NVPAIR	( 16 * 1024ULL)
 #define VDEV_LABEL_SIZE		(256 * 1024ULL)
 #define UBERBLOCK_SIZE		1024ULL
+#define UBERBLOCKS_COUNT   128
 
 /* #include <sys/uberblock_impl.h> */
 #define UBERBLOCK_MAGIC         0x00bab10c              /* oo-ba-bloc!  */
@@ -32,7 +33,6 @@ struct zfs_uberblock {
 	char		ub_rootbp;	/* MOS objset_phys_t		*/
 } __attribute__((packed));
 
-#define ZFS_TRIES	512
 #define ZFS_WANT	 4
 
 #define DATA_TYPE_UINT64 8
@@ -163,61 +163,82 @@ static void zfs_extract_guid_name(blkid_probe pr, loff_t offset)
 #define zdebug(fmt, ...)	do {} while(0)
 /*#define zdebug(fmt, a...)	fprintf(stderr, fmt, ##a)*/
 
-/* ZFS has 128x1kB host-endian root blocks, stored in 2 areas (labels)
- * at the start of the disk, and 2 areas at the end of the disk.
- */
+static int find_uberblocks(const void *label, loff_t *ub_offset, int *swap_endian)
+{
+	uint64_t swab_magic = swab64(UBERBLOCK_MAGIC);
+	struct zfs_uberblock *ub;
+	int i, found = 0;
+	loff_t offset = VDEV_LABEL_UBERBLOCK;
+
+	for (i = 0; i < UBERBLOCKS_COUNT; i++, offset += UBERBLOCK_SIZE) {
+		ub = (struct zfs_uberblock *)(label + offset);
+
+		if (ub->ub_magic == UBERBLOCK_MAGIC) {
+			*ub_offset = offset;
+			*swap_endian = 0;
+			found++;
+			zdebug("probe_zfs: found little-endian uberblock at %llu\n", offset >> 10);
+		}
+
+		if (ub->ub_magic == swab_magic) {
+			*ub_offset = offset;
+			*swap_endian = 1;
+			found++;
+			zdebug("probe_zfs: found big-endian uberblock at %llu\n", offset >> 10);
+		}
+  }
+
+  return found;
+}
+
+/* ZFS has 128x1kB host-endian root blocks, stored in 2 areas at the start
+ * of the disk, and 2 areas at the end of the disk.  Check only some of them...
+ * #4 (@ 132kB) is the first one written on a new filesystem. */
 static int probe_zfs(blkid_probe pr, const struct blkid_idmag *mag)
 {
 	uint64_t swab_magic = swab64(UBERBLOCK_MAGIC);
+	int swab_endian = 0;
 	struct zfs_uberblock *ub;
-	int swab_endian;
 	loff_t offset, ub_offset = 0;
-	int tried;
-	int found;
+	int label_no, found = 0, found_in_label;
+	void *label;
 	loff_t blk_align = (pr->size % (256 * 1024ULL));
 
 	zdebug("probe_zfs\n");
-	/* Look for at least 4 uberblocks to ensure a positive match.
-	   Begin with Label 0 (L0) at the start of the block device. */
-	for (tried = found = 0, offset = VDEV_LABEL_UBERBLOCK;
-	     found < ZFS_WANT && tried < ZFS_TRIES;
-	     tried++, offset += UBERBLOCK_SIZE)
-	{
-		/* Leave L0 to try other labels */
-		switch(tried) {
-		case 128: // jump to L1, just after L0
-			offset = VDEV_LABEL_SIZE + VDEV_LABEL_UBERBLOCK;
+	/* Look for at least 4 uberblocks to ensure a positive match */
+	for (label_no = 0; label_no < 4; label_no++) {
+		switch(label_no) {
+		case 0: // jump to L0
+			offset = 0;
 			break;
-		case 256: // jump to L2 near the far end of the block device
-			offset = pr->size - 2 * VDEV_LABEL_SIZE + VDEV_LABEL_UBERBLOCK - blk_align;
-			zdebug("probe_zfs: l2 offset %llu\n", offset >> 10);
+		case 1: // jump to L1
+			offset = VDEV_LABEL_SIZE;
 			break;
-		case 384: // jump to L3 at the furthest end of the block device
-			offset = pr->size - VDEV_LABEL_SIZE + VDEV_LABEL_UBERBLOCK - blk_align;
-			zdebug("probe_zfs: l3 offset %llu\n", offset >> 10);
+		case 2: // jump to L2
+			offset = pr->size - 2 * VDEV_LABEL_SIZE - blk_align;
+			break;
+		case 3: // jump to L3
+			offset = pr->size - VDEV_LABEL_SIZE - blk_align;
 			break;
 		}
 
-		ub = (struct zfs_uberblock *)
-			blkid_probe_get_buffer(pr, offset,
-					       sizeof(struct zfs_uberblock));
-		if (ub == NULL)
+		label = blkid_probe_get_buffer(pr, offset, VDEV_LABEL_SIZE);
+		if (label == NULL)
 			return errno ? -errno : 1;
 
-		if (ub->ub_magic == UBERBLOCK_MAGIC) {
-			ub_offset = offset;
-			found++;
-			zdebug("probe_zfs: found little-endian uberblock at %llu\n", offset >> 10);
-		}
+		found_in_label = find_uberblocks(label, &ub_offset, &swab_endian);
 
-		if ((swab_endian = (ub->ub_magic == swab_magic))) {
-			ub_offset = offset;
-			found++;
-			zdebug("probe_zfs: found big-endian uberblock at %llu\n", offset >> 10);
+		if (found_in_label > 0) {
+			found+= found_in_label;
+			ub = (struct zfs_uberblock *)(label + ub_offset);
+			ub_offset += offset;
+
+			if (found >= ZFS_WANT)
+				break;
 		}
 	}
 
-	if (found < 4)
+	if (found < ZFS_WANT)
 		return 1;
 
 	/* If we found the 4th uberblock, then we will have exited from the