diff -up util-linux-2.23.2/libblkid/src/superblocks/superblocks.c.kzak util-linux-2.23.2/libblkid/src/superblocks/superblocks.c

--- util-linux-2.23.2/libblkid/src/superblocks/superblocks.c.kzak	2015-06-24 12:58:20.790115492 +0200

+++ util-linux-2.23.2/libblkid/src/superblocks/superblocks.c	2015-06-24 12:57:57.961286166 +0200

@@ -49,6 +49,8 @@

  *

  * @UUID_SUB: subvolume uuid (e.g. btrfs)

  *

+ * @LOGUUID: external log UUID (e.g. xfs)

+ *

  * @UUID_RAW: raw UUID from FS superblock

  *

  * @EXT_JOURNAL: external journal UUID

@@ -113,6 +115,7 @@ static const struct blkid_idinfo *idinfo

 	&swsuspend_idinfo,

 	&swap_idinfo,

 	&xfs_idinfo,

+	&xfs_log_idinfo,

 	&ext4dev_idinfo,

 	&ext4_idinfo,

 	&ext3_idinfo,

diff -up util-linux-2.23.2/libblkid/src/superblocks/superblocks.h.kzak util-linux-2.23.2/libblkid/src/superblocks/superblocks.h

--- util-linux-2.23.2/libblkid/src/superblocks/superblocks.h.kzak	2015-06-24 12:58:48.533908071 +0200

+++ util-linux-2.23.2/libblkid/src/superblocks/superblocks.h	2015-06-24 12:59:00.098821476 +0200

@@ -29,6 +29,7 @@ extern const struct blkid_idinfo ext2_id

 extern const struct blkid_idinfo jbd_idinfo;

 extern const struct blkid_idinfo jfs_idinfo;

 extern const struct blkid_idinfo xfs_idinfo;

+extern const struct blkid_idinfo xfs_log_idinfo;

 extern const struct blkid_idinfo gfs_idinfo;

 extern const struct blkid_idinfo gfs2_idinfo;

 extern const struct blkid_idinfo romfs_idinfo;

diff -up util-linux-2.23.2/libblkid/src/superblocks/xfs.c.kzak util-linux-2.23.2/libblkid/src/superblocks/xfs.c

--- util-linux-2.23.2/libblkid/src/superblocks/xfs.c.kzak	2015-06-24 12:39:34.300507071 +0200

+++ util-linux-2.23.2/libblkid/src/superblocks/xfs.c	2015-06-24 12:39:45.389427015 +0200

@@ -4,6 +4,7 @@

  * Copyright (C) 2001 by Andreas Dilger

  * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>

  * Copyright (C) 2008 Karel Zak <kzak@redhat.com>

+ * Copyright (C) 2013 Eric Sandeen <sandeen@redhat.com>

  *

  * This file may be redistributed under the terms of the

  * GNU Lesser General Public License.

@@ -187,3 +188,90 @@ const struct blkid_idinfo xfs_idinfo =

 	}

 };

+struct xlog_rec_header {

+	uint32_t	h_magicno;

+	uint32_t	h_dummy1[1];

+	uint32_t	h_version;

+	uint32_t	h_len;

+	uint32_t	h_dummy2[71];

+	uint32_t	h_fmt;

+	unsigned char	h_uuid[16];

+} __attribute__((packed));

+

+#define XLOG_HEADER_MAGIC_NUM 0xFEEDbabe

+

+/*

+ * For very small filesystems, the minimum log size

+ * can be smaller, but that seems vanishingly unlikely

+ * when used with an external log (which is used for

+ * performance reasons; tiny conflicts with that goal).

+ */

+#define XFS_MIN_LOG_BYTES	(10 * 1024 * 1024)

+

+#define XLOG_FMT_LINUX_LE	1

+#define XLOG_FMT_LINUX_BE	2

+#define XLOG_FMT_IRIX_BE	3

+

+#define XLOG_VERSION_1		1

+#define XLOG_VERSION_2		2	/* Large IClogs, Log sunit */

+#define XLOG_VERSION_OKBITS	(XLOG_VERSION_1 | XLOG_VERSION_2)

+

+static int xlog_valid_rec_header(struct xlog_rec_header *rhead)

+{

+	uint32_t hlen;

+

+	if (rhead->h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM))

+		return 0;

+

+	if (!rhead->h_version ||

+            (be32_to_cpu(rhead->h_version) & (~XLOG_VERSION_OKBITS)))

+		return 0;

+

+	/* LR body must have data or it wouldn't have been written */

+	hlen = be32_to_cpu(rhead->h_len);

+	if (hlen <= 0 || hlen > INT_MAX)

+		return 0;

+

+	if (rhead->h_fmt != cpu_to_be32(XLOG_FMT_LINUX_LE) &&

+	    rhead->h_fmt != cpu_to_be32(XLOG_FMT_LINUX_BE) &&

+	    rhead->h_fmt != cpu_to_be32(XLOG_FMT_IRIX_BE))

+		return 0;

+

+	return 1;

+}

+

+/* xlog record header will be in some sector in the first 256k */

+static int probe_xfs_log(blkid_probe pr, const struct blkid_idmag *mag)

+{

+	int i;

+	struct xlog_rec_header *rhead;

+	unsigned char *buf;

+

+	buf = blkid_probe_get_buffer(pr, 0, 256*1024);

+	if (!buf)

+		return errno ? -errno : 1;

+

+	if (memcmp(buf, "XFSB", 4) == 0)

+		return 1;			/* this is regular XFS, ignore */

+

+	/* check the first 512 512-byte sectors */

+	for (i = 0; i < 512; i++) {

+		rhead = (struct xlog_rec_header *)&buf[i*512];

+

+		if (xlog_valid_rec_header(rhead)) {

+			blkid_probe_set_uuid_as(pr, rhead->h_uuid, "LOGUUID");

+			return 0;

+		}

+	}

+

+	return 1;

+}

+

+const struct blkid_idinfo xfs_log_idinfo =

+{

+	.name		= "xfs_external_log",

+	.usage		= BLKID_USAGE_OTHER,

+	.probefunc	= probe_xfs_log,

+	.magics		= BLKID_NONE_MAGIC,

+	.minsz		= XFS_MIN_LOG_BYTES,

+};