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From 8646f60d1b421b48b43405fa286548a0bf3f5da4 Mon Sep 17 00:00:00 2001
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From: Michal Humpula <michal.humpula@hudrydum.cz>
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Date: Sat, 28 Feb 2015 21:19:42 +0100
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Subject: [PATCH 109/116] zfs: make less syscalls
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Upstream: https://github.com/karelzak/util-linux/commit/e44a4c7ac9522c03b76d8b62ce88b443771fdb0b
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Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1392661
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Signed-off-by: Karel Zak <kzak@redhat.com>
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---
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 libblkid/src/superblocks/zfs.c | 95 ++++++++++++++++++++++++++----------------
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 1 file changed, 58 insertions(+), 37 deletions(-)
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diff --git a/libblkid/src/superblocks/zfs.c b/libblkid/src/superblocks/zfs.c
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index 4a64a03..9b5601e 100644
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--- a/libblkid/src/superblocks/zfs.c
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+++ b/libblkid/src/superblocks/zfs.c
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@@ -20,6 +20,7 @@
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 #define VDEV_LABEL_NVPAIR	( 16 * 1024ULL)
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 #define VDEV_LABEL_SIZE		(256 * 1024ULL)
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 #define UBERBLOCK_SIZE		1024ULL
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+#define UBERBLOCKS_COUNT   128
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 /* #include <sys/uberblock_impl.h> */
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 #define UBERBLOCK_MAGIC         0x00bab10c              /* oo-ba-bloc!  */
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@@ -32,7 +33,6 @@ struct zfs_uberblock {
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 	char		ub_rootbp;	/* MOS objset_phys_t		*/
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 } __attribute__((packed));
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-#define ZFS_TRIES	512
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 #define ZFS_WANT	 4
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 #define DATA_TYPE_UINT64 8
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@@ -163,61 +163,82 @@ static void zfs_extract_guid_name(blkid_probe pr, loff_t offset)
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 #define zdebug(fmt, ...)	do {} while(0)
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 /*#define zdebug(fmt, a...)	fprintf(stderr, fmt, ##a)*/
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-/* ZFS has 128x1kB host-endian root blocks, stored in 2 areas (labels)
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- * at the start of the disk, and 2 areas at the end of the disk.
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- */
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+static int find_uberblocks(const void *label, loff_t *ub_offset, int *swap_endian)
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+{
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+	uint64_t swab_magic = swab64(UBERBLOCK_MAGIC);
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+	struct zfs_uberblock *ub;
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+	int i, found = 0;
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+	loff_t offset = VDEV_LABEL_UBERBLOCK;
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+
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+	for (i = 0; i < UBERBLOCKS_COUNT; i++, offset += UBERBLOCK_SIZE) {
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+		ub = (struct zfs_uberblock *)(label + offset);
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+
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+		if (ub->ub_magic == UBERBLOCK_MAGIC) {
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+			*ub_offset = offset;
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+			*swap_endian = 0;
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+			found++;
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+			zdebug("probe_zfs: found little-endian uberblock at %llu\n", offset >> 10);
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+		}
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+
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+		if (ub->ub_magic == swab_magic) {
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+			*ub_offset = offset;
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+			*swap_endian = 1;
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+			found++;
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+			zdebug("probe_zfs: found big-endian uberblock at %llu\n", offset >> 10);
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+		}
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+  }
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+
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+  return found;
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+}
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+
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+/* ZFS has 128x1kB host-endian root blocks, stored in 2 areas at the start
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+ * of the disk, and 2 areas at the end of the disk.  Check only some of them...
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+ * #4 (@ 132kB) is the first one written on a new filesystem. */
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 static int probe_zfs(blkid_probe pr, const struct blkid_idmag *mag)
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 {
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 	uint64_t swab_magic = swab64(UBERBLOCK_MAGIC);
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+	int swab_endian = 0;
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 	struct zfs_uberblock *ub;
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-	int swab_endian;
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 	loff_t offset, ub_offset = 0;
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-	int tried;
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-	int found;
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+	int label_no, found = 0, found_in_label;
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+	void *label;
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 	loff_t blk_align = (pr->size % (256 * 1024ULL));
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 	zdebug("probe_zfs\n");
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-	/* Look for at least 4 uberblocks to ensure a positive match.
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-	   Begin with Label 0 (L0) at the start of the block device. */
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-	for (tried = found = 0, offset = VDEV_LABEL_UBERBLOCK;
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-	     found < ZFS_WANT && tried < ZFS_TRIES;
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-	     tried++, offset += UBERBLOCK_SIZE)
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-	{
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-		/* Leave L0 to try other labels */
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-		switch(tried) {
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-		case 128: // jump to L1, just after L0
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-			offset = VDEV_LABEL_SIZE + VDEV_LABEL_UBERBLOCK;
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+	/* Look for at least 4 uberblocks to ensure a positive match */
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+	for (label_no = 0; label_no < 4; label_no++) {
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+		switch(label_no) {
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+		case 0: // jump to L0
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+			offset = 0;
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 			break;
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-		case 256: // jump to L2 near the far end of the block device
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-			offset = pr->size - 2 * VDEV_LABEL_SIZE + VDEV_LABEL_UBERBLOCK - blk_align;
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-			zdebug("probe_zfs: l2 offset %llu\n", offset >> 10);
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+		case 1: // jump to L1
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+			offset = VDEV_LABEL_SIZE;
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 			break;
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-		case 384: // jump to L3 at the furthest end of the block device
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-			offset = pr->size - VDEV_LABEL_SIZE + VDEV_LABEL_UBERBLOCK - blk_align;
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-			zdebug("probe_zfs: l3 offset %llu\n", offset >> 10);
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+		case 2: // jump to L2
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+			offset = pr->size - 2 * VDEV_LABEL_SIZE - blk_align;
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+			break;
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+		case 3: // jump to L3
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+			offset = pr->size - VDEV_LABEL_SIZE - blk_align;
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 			break;
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 		}
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-		ub = (struct zfs_uberblock *)
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-			blkid_probe_get_buffer(pr, offset,
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-					       sizeof(struct zfs_uberblock));
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-		if (ub == NULL)
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+		label = blkid_probe_get_buffer(pr, offset, VDEV_LABEL_SIZE);
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+		if (label == NULL)
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 			return errno ? -errno : 1;
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-		if (ub->ub_magic == UBERBLOCK_MAGIC) {
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-			ub_offset = offset;
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-			found++;
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-			zdebug("probe_zfs: found little-endian uberblock at %llu\n", offset >> 10);
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-		}
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+		found_in_label = find_uberblocks(label, &ub_offset, &swab_endian);
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-		if ((swab_endian = (ub->ub_magic == swab_magic))) {
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-			ub_offset = offset;
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-			found++;
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-			zdebug("probe_zfs: found big-endian uberblock at %llu\n", offset >> 10);
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+		if (found_in_label > 0) {
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+			found+= found_in_label;
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+			ub = (struct zfs_uberblock *)(label + ub_offset);
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+			ub_offset += offset;
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+
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+			if (found >= ZFS_WANT)
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+				break;
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 		}
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 	}
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-	if (found < 4)
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+	if (found < ZFS_WANT)
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 		return 1;
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 	/* If we found the 4th uberblock, then we will have exited from the
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-- 
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2.9.3
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