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diff -up util-linux-2.23.2/libblkid/src/superblocks/superblocks.c.kzak util-linux-2.23.2/libblkid/src/superblocks/superblocks.c
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--- util-linux-2.23.2/libblkid/src/superblocks/superblocks.c.kzak	2015-06-24 12:58:20.790115492 +0200
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+++ util-linux-2.23.2/libblkid/src/superblocks/superblocks.c	2015-06-24 12:57:57.961286166 +0200
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@@ -49,6 +49,8 @@
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  *
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  * @UUID_SUB: subvolume uuid (e.g. btrfs)
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  *
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+ * @LOGUUID: external log UUID (e.g. xfs)
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+ *
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  * @UUID_RAW: raw UUID from FS superblock
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  *
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  * @EXT_JOURNAL: external journal UUID
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@@ -113,6 +115,7 @@ static const struct blkid_idinfo *idinfo
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 	&swsuspend_idinfo,
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 	&swap_idinfo,
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 	&xfs_idinfo,
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+	&xfs_log_idinfo,
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 	&ext4dev_idinfo,
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 	&ext4_idinfo,
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 	&ext3_idinfo,
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diff -up util-linux-2.23.2/libblkid/src/superblocks/superblocks.h.kzak util-linux-2.23.2/libblkid/src/superblocks/superblocks.h
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--- util-linux-2.23.2/libblkid/src/superblocks/superblocks.h.kzak	2015-06-24 12:58:48.533908071 +0200
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+++ util-linux-2.23.2/libblkid/src/superblocks/superblocks.h	2015-06-24 12:59:00.098821476 +0200
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@@ -29,6 +29,7 @@ extern const struct blkid_idinfo ext2_id
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 extern const struct blkid_idinfo jbd_idinfo;
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 extern const struct blkid_idinfo jfs_idinfo;
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 extern const struct blkid_idinfo xfs_idinfo;
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+extern const struct blkid_idinfo xfs_log_idinfo;
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 extern const struct blkid_idinfo gfs_idinfo;
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 extern const struct blkid_idinfo gfs2_idinfo;
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 extern const struct blkid_idinfo romfs_idinfo;
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diff -up util-linux-2.23.2/libblkid/src/superblocks/xfs.c.kzak util-linux-2.23.2/libblkid/src/superblocks/xfs.c
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--- util-linux-2.23.2/libblkid/src/superblocks/xfs.c.kzak	2015-06-24 12:39:34.300507071 +0200
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+++ util-linux-2.23.2/libblkid/src/superblocks/xfs.c	2015-06-24 12:39:45.389427015 +0200
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@@ -4,6 +4,7 @@
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  * Copyright (C) 2001 by Andreas Dilger
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  * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
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  * Copyright (C) 2008 Karel Zak <kzak@redhat.com>
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+ * Copyright (C) 2013 Eric Sandeen <sandeen@redhat.com>
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  *
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  * This file may be redistributed under the terms of the
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  * GNU Lesser General Public License.
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@@ -187,3 +188,90 @@ const struct blkid_idinfo xfs_idinfo =
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 	}
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 };
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+struct xlog_rec_header {
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+	uint32_t	h_magicno;
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+	uint32_t	h_dummy1[1];
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+	uint32_t	h_version;
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+	uint32_t	h_len;
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+	uint32_t	h_dummy2[71];
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+	uint32_t	h_fmt;
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+	unsigned char	h_uuid[16];
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+} __attribute__((packed));
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+
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+#define XLOG_HEADER_MAGIC_NUM 0xFEEDbabe
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+
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+/*
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+ * For very small filesystems, the minimum log size
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+ * can be smaller, but that seems vanishingly unlikely
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+ * when used with an external log (which is used for
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+ * performance reasons; tiny conflicts with that goal).
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+ */
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+#define XFS_MIN_LOG_BYTES	(10 * 1024 * 1024)
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+
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+#define XLOG_FMT_LINUX_LE	1
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+#define XLOG_FMT_LINUX_BE	2
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+#define XLOG_FMT_IRIX_BE	3
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+
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+#define XLOG_VERSION_1		1
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+#define XLOG_VERSION_2		2	/* Large IClogs, Log sunit */
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+#define XLOG_VERSION_OKBITS	(XLOG_VERSION_1 | XLOG_VERSION_2)
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+
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+static int xlog_valid_rec_header(struct xlog_rec_header *rhead)
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+{
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+	uint32_t hlen;
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+
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+	if (rhead->h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM))
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+		return 0;
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+
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+	if (!rhead->h_version ||
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+            (be32_to_cpu(rhead->h_version) & (~XLOG_VERSION_OKBITS)))
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+		return 0;
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+
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+	/* LR body must have data or it wouldn't have been written */
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+	hlen = be32_to_cpu(rhead->h_len);
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+	if (hlen <= 0 || hlen > INT_MAX)
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+		return 0;
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+
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+	if (rhead->h_fmt != cpu_to_be32(XLOG_FMT_LINUX_LE) &&
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+	    rhead->h_fmt != cpu_to_be32(XLOG_FMT_LINUX_BE) &&
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+	    rhead->h_fmt != cpu_to_be32(XLOG_FMT_IRIX_BE))
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+		return 0;
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+
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+	return 1;
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+}
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+
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+/* xlog record header will be in some sector in the first 256k */
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+static int probe_xfs_log(blkid_probe pr, const struct blkid_idmag *mag)
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+{
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+	int i;
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+	struct xlog_rec_header *rhead;
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+	unsigned char *buf;
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+
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+	buf = blkid_probe_get_buffer(pr, 0, 256*1024);
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+	if (!buf)
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+		return errno ? -errno : 1;
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+
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+	if (memcmp(buf, "XFSB", 4) == 0)
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+		return 1;			/* this is regular XFS, ignore */
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+
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+	/* check the first 512 512-byte sectors */
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+	for (i = 0; i < 512; i++) {
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+		rhead = (struct xlog_rec_header *)&buf[i*512];
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+
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+		if (xlog_valid_rec_header(rhead)) {
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+			blkid_probe_set_uuid_as(pr, rhead->h_uuid, "LOGUUID");
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+			return 0;
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+		}
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+	}
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+
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+	return 1;
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+}
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+
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+const struct blkid_idinfo xfs_log_idinfo =
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+{
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+	.name		= "xfs_external_log",
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+	.usage		= BLKID_USAGE_OTHER,
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+	.probefunc	= probe_xfs_log,
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+	.magics		= BLKID_NONE_MAGIC,
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+	.minsz		= XFS_MIN_LOG_BYTES,
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+};