[PATCH] libblkid: support for GUID Partition Table (GPT), please?

[PATCH] libblkid: support for GUID Partition Table (GPT), please?

[Ivan Shmakov]

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	GPT contains a supposed to be unique “Disk GUID” field, which
	allows for the media bearing such a partition table to be
	identified.

	May I suggest adding support for GPT to libblkid?  An
	alpha-quality patch is MIME'd.

-- 
FSF associate member #7257

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diff --git a/lib/blkid/probe.c b/lib/blkid/probe.c
index 6b75732..0e6c70d 100644
--- a/lib/blkid/probe.c
+++ b/lib/blkid/probe.c
@@ -1383,6 +1383,28 @@ static int probe_btrfs(struct blkid_probe *probe,
 	set_uuid(probe->dev, bs->fsid, 0);
 	return 0;
 }
+
+static int probe_gpt (struct blkid_probe *probe,
+                      struct blkid_magic *id,
+                      unsigned char *buf)
+{
+	struct gpt_header *gh
+		= (struct gpt_header *)(buf + 0x200);
+
+	/* FIXME: check gh->header_crc32 */
+
+	{
+		__u64 uuid;
+		char uuid_str[17];
+
+		uuid = blkid_le64 (*((__u64 *)gh->disk_guid));
+		sprintf (uuid_str, "%016llX", uuid);
+		blkid_set_tag (probe->dev, "UUID", uuid_str, 0);
+	}
+
+	return 0;
+}
+
 /*
  * Various filesystem magics that we can check for.  Note that kboff and
  * sboff are in kilobytes and bytes respectively.  All magics are in
@@ -1482,6 +1504,7 @@ static struct blkid_magic type_array[] = {
   { "lvm2pv",	 1,  0x018,  8, "LVM2 001",		probe_lvm2 },
   { "lvm2pv",	 1,  0x218,  8, "LVM2 001",		probe_lvm2 },
   { "btrfs",	 64,  0x40,  8, "_BHRfS_M",		probe_btrfs },
+  { "gpt",       0,  0x200,  8, "EFI PART",             probe_gpt },
   {   NULL,	 0,	 0,  0, NULL,			NULL }
 };
 
diff --git a/lib/blkid/probe.h b/lib/blkid/probe.h
index 37fc9c0..4d39b84 100644
--- a/lib/blkid/probe.h
+++ b/lib/blkid/probe.h
@@ -725,6 +725,28 @@ struct btrfs_super_block {
 	__u8 sys_chunk_array[BTRFS_SYSTEM_CHUNK_ARRAY_SIZE];
 } __attribute__ ((__packed__));
 
+struct gpt_header {
+	/* references:
+	 *   * linux/include/linux/efi.h;
+	 *   * Wikipedia entry.
+	 */
+	__u64 signature;
+	__u32 revision;
+	__u32 header_size;
+	__u32 header_crc32;
+	__u32 reserved1;
+	__u64 my_lba;
+	__u64 alternate_lba;
+	__u64 first_usable_lba;
+	__u64 last_usable_lba;
+	__u8 disk_guid[16];
+	__u64 partition_entry_lba;
+	__u32 num_partition_entries;
+	__u32 sizeof_partition_entry;
+	__u32 partition_entry_array_crc32;
+	__u8 reserved2[512 - 92];
+} __attribute__ ((__packed__));
+
 /*
  * Byte swap functions
  */

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Re: [PATCH] libblkid: support for GUID Partition Table (GPT), please?

[Ivan Shmakov]

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>>>>> "IS" == Ivan Shmakov <ivan@main.uusia.org> writes:

 IS> GPT contains a supposed to be unique “Disk GUID” field, which
 IS> allows for the media bearing such a partition table to be
 IS> identified.

 IS> May I suggest adding support for GPT to libblkid?  An alpha-quality
 IS> patch is MIME'd.

	Ahem.  Wrong copy-paste late at night.  Should be better this
	time.

	For a test:

$ blkid -t TYPE=gpt /dev/sd? 
/dev/sdb: UUID="CE050C6F-E7BE-AD46-8FEE-F02476EC767E" TYPE="gpt" 
/dev/sdd: UUID="2A1210B5-535F-4A4A-84D0-34ABC6E57FFB" TYPE="gpt" 
/dev/sde: UUID="7B0FA8C6-26DD-1840-BBF5-46AD26CA551C" TYPE="gpt" 
/dev/sdf: UUID="04DF9DE5-CFDA-514D-99B7-CC61061FCE3C" TYPE="gpt" 
$ 

	Please note that the CRC-32 value contained in the GPT is not
	checked.

	The UUID could be printed in lower case instead.

-- 
FSF associate member #7257

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diff --git a/lib/blkid/probe.c b/lib/blkid/probe.c
index 6b75732..8500320 100644
--- a/lib/blkid/probe.c
+++ b/lib/blkid/probe.c
@@ -1383,6 +1383,33 @@ static int probe_btrfs(struct blkid_probe *probe,
 	set_uuid(probe->dev, bs->fsid, 0);
 	return 0;
 }
+
+static int probe_gpt (struct blkid_probe *probe,
+                      struct blkid_magic *id,
+                      unsigned char *buf)
+{
+	struct gpt_header *gh
+		= (struct gpt_header *)(buf + 0x200);
+
+	/* FIXME: check gh->header_crc32 */
+
+	{
+		const __u8 *u = gh->disk_guid;
+		char uuid_str[33];
+
+		sprintf (uuid_str,
+			 ("%02X%02X%02X%02X"
+			  "-%02X%02X-%02X%02X-%02X%02X"
+			  "-%02X%02X%02X%02X%02X%02X"),
+			 u[0], u[1], u[2], u[3],
+			 u[4], u[5], u[6], u[7], u[8], u[9],
+			 u[10], u[11], u[12], u[13], u[14], u[15]);
+		blkid_set_tag (probe->dev, "UUID", uuid_str, 0);
+	}
+
+	return 0;
+}
+
 /*
  * Various filesystem magics that we can check for.  Note that kboff and
  * sboff are in kilobytes and bytes respectively.  All magics are in
@@ -1482,6 +1509,7 @@ static struct blkid_magic type_array[] = {
   { "lvm2pv",	 1,  0x018,  8, "LVM2 001",		probe_lvm2 },
   { "lvm2pv",	 1,  0x218,  8, "LVM2 001",		probe_lvm2 },
   { "btrfs",	 64,  0x40,  8, "_BHRfS_M",		probe_btrfs },
+  { "gpt",       0,  0x200,  8, "EFI PART",             probe_gpt },
   {   NULL,	 0,	 0,  0, NULL,			NULL }
 };
 
diff --git a/lib/blkid/probe.h b/lib/blkid/probe.h
index 37fc9c0..4d39b84 100644
--- a/lib/blkid/probe.h
+++ b/lib/blkid/probe.h
@@ -725,6 +725,28 @@ struct btrfs_super_block {
 	__u8 sys_chunk_array[BTRFS_SYSTEM_CHUNK_ARRAY_SIZE];
 } __attribute__ ((__packed__));
 
+struct gpt_header {
+	/* references:
+	 *   * linux/include/linux/efi.h;
+	 *   * Wikipedia entry.
+	 */
+	__u64 signature;
+	__u32 revision;
+	__u32 header_size;
+	__u32 header_crc32;
+	__u32 reserved1;
+	__u64 my_lba;
+	__u64 alternate_lba;
+	__u64 first_usable_lba;
+	__u64 last_usable_lba;
+	__u8 disk_guid[16];
+	__u64 partition_entry_lba;
+	__u32 num_partition_entries;
+	__u32 sizeof_partition_entry;
+	__u32 partition_entry_array_crc32;
+	__u8 reserved2[512 - 92];
+} __attribute__ ((__packed__));
+
 /*
  * Byte swap functions
  */

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Re: [PATCH] libblkid: support for GUID Partition Table (GPT), please?

[Karel Zak]

On Sat, May 15, 2010 at 10:06:23AM +0700, Ivan Shmakov wrote:
> >>>>> "IS" == Ivan Shmakov <ivan@main.uusia.org> writes:
> 
>  IS> GPT contains a supposed to be unique “Disk GUID” field, which
>  IS> allows for the media bearing such a partition table to be
>  IS> identified.

 The devel version of libblkid from util-linux-ng supports partition tables
 parsing, and the partition name (GPT nad Mac) and partition UUID (only GPT)
 are exported to udev. For example:

   # blkid -p -o udev /dev/sdb1
   ID_PART_ENTRY_SCHEME=gpt
   ID_PART_ENTRY_NAME=ThisIsName
   ID_PART_ENTRY_UUID=bc10cf1d-7e63-524c-8203-087ae10a820b
   ID_PART_ENTRY_TYPE=a2a0d0eb-e5b9-3344-87c0-68b6b72699c7
   ID_PART_ENTRY_NUMBER=1

 In my TODO list is to support partition identifiers for standard
 operations like mount/fsck, something like:

   # mount PARTUUID=bc10cf1d-7e63-524c-8203-087ae10a820b /mnt
 or
   # mount PARTLABEL=ThisIsName /mnt
 
 Comments?

    Karel

-- 
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 http://karelzak.blogspot.com
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Re: [PATCH] libblkid: support for GUID Partition Table (GPT), please?

[Ivan Shmakov]

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>>>>> Karel Zak <kzak@redhat.com> writes:
>>>>> Ivan Shmakov <ivan@main.uusia.org> writes:

 >>> GPT contains a supposed to be unique “Disk GUID” field, which allows
 >>> for the media bearing such a partition table to be identified.

 > The devel version of libblkid from util-linux-ng supports partition
 > tables parsing, and the partition name (GPT nad Mac) and partition
 > UUID (only GPT) are exported to udev.

	I don't quite understand how udev is tied here, but please note
	that the UUID I was talking above is the one associated with the
	partition table as a whole, not with a particular partition.

	(Huh?  util-linux-ng has its own libblkid?  And, BTW, any chance
	of having the changes accepted into e2fsprogs?)

	Such a UUID allows for removable media to be identified, which,
	in turn, allows for automated backups for such media.
	(Consider, e. g., that one has a bunch of bootable USB flash
	drives.  From time to time, the OS'es are upgraded; and there
	may be problems with newer versions.  The possibility of
	restoring the bootable image to the state it had at a certain
	time could then become extremly handy.)

	(Actually, I've just finished with the design of such a backup
	scheme, and it relies on the media — or partition table —
	UUID's, Sleuthkit and, to preserve disk space, Jigdo.  Hopefully
	I'd be able to describe it at my “hacks collection” [1] soon.)

[1] http://lhc.am-1.org/lhc/users/ivan_shmakov/

 > For example:

 > # blkid -p -o udev /dev/sdb1
 > ID_PART_ENTRY_SCHEME=gpt
 > ID_PART_ENTRY_NAME=ThisIsName
 > ID_PART_ENTRY_UUID=bc10cf1d-7e63-524c-8203-087ae10a820b
 > ID_PART_ENTRY_TYPE=a2a0d0eb-e5b9-3344-87c0-68b6b72699c7
 > ID_PART_ENTRY_NUMBER=1

 > In my TODO list is to support partition identifiers for standard
 > operations like mount/fsck, something like:

 > # mount PARTUUID=bc10cf1d-7e63-524c-8203-087ae10a820b /mnt
 > or
 > # mount PARTLABEL=ThisIsName /mnt

 > Comments?

	Well, to my mind, allowing UUID's that are stored in the
	partition table could be useful in two cases:

	• the filesystem contained on a partition doesn't allow for a
	  UUID;

	• the filesystem is ought to be re-initialized (either to the
	  same filesystem type or any other one) from time to time.

	Although I consider both of the above somewhat unlikely in my
	current practice, I don't see any harm of having such a feature
	“just for a case”.

	The labels are a bit useless, to my mind, since when one does
	mount(8) or fsck(8) by hand, it's usually when one does it with
	the medium attached to a host other than it was usually attached
	to.  There, a name clash is quite likely.

-- 
FSF associate member #7257

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Re: [PATCH] libblkid: support for GUID Partition Table (GPT), please?

[tytso]

On Mon, May 17, 2010 at 08:45:10PM +0700, Ivan Shmakov wrote:
> 
> 	(Huh?  util-linux-ng has its own libblkid?  And, BTW, any chance
> 	of having the changes accepted into e2fsprogs?)

The blkid library has been transitioned to util-linux-ng.  I'll put in
critical bug fixes, but at this point, there is significant new
functionality in the version of blkid in util-linux-ng, and the major
distributions are using the one from util-linux-ng.

	      	  	    	     - Ted