Commit d33b98fc authored by Stephen Warren's avatar Stephen Warren Committed by Jens Axboe
Browse files

block: partition: msdos: provide UUIDs for partitions 



The MSDOS/MBR partition table includes a 32-bit unique ID, often referred
to as the NT disk signature.  When combined with a partition number within
the table, this can form a unique ID similar in concept to EFI/GPT's
partition UUID.  Constructing and recording this value in struct
partition_meta_info allows MSDOS partitions to be referred to on the
kernel command-line using the following syntax:

root=PARTUUID=0002dd75-01

Signed-off-by: default avatarStephen Warren <swarren@nvidia.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 283f8fc0

block/partitions/msdos.c

+19 −2
Original line number Diff line number Diff line
@@ -94,6 +94,17 @@ static int aix_magic_present(struct parsed_partitions *state, unsigned char *p) 
	return ret;

}



static void set_info(struct parsed_partitions *state, int slot,

		     u32 disksig)

{

	struct partition_meta_info *info = &state->parts[slot].info;



	snprintf(info->uuid, sizeof(info->uuid), "%08x-%02x", disksig,

		 slot);

	info->volname[0] = 0;

	state->parts[slot].has_info = true;

}



/*

 * Create devices for each logical partition in an extended partition.

 * The logical partitions form a linked list, with each entry being
@@ -106,7 +117,8 @@ static int aix_magic_present(struct parsed_partitions *state, unsigned char *p) 
 */



static void parse_extended(struct parsed_partitions *state,

			   sector_t first_sector, sector_t first_size)

			   sector_t first_sector, sector_t first_size,

			   u32 disksig)

{

	struct partition *p;

	Sector sect;
@@ -166,6 +178,7 @@ static void parse_extended(struct parsed_partitions *state, 
			}



			put_partition(state, state->next, next, size);

			set_info(state, state->next, disksig);

			if (SYS_IND(p) == LINUX_RAID_PARTITION)

				state->parts[state->next].flags = ADDPART_FLAG_RAID;

			loopct = 0;
@@ -437,6 +450,7 @@ int msdos_partition(struct parsed_partitions *state) 
	struct partition *p;

	struct fat_boot_sector *fb;

	int slot;

	u32 disksig;



	data = read_part_sector(state, 0, &sect);

	if (!data)
@@ -491,6 +505,8 @@ int msdos_partition(struct parsed_partitions *state) 
#endif

	p = (struct partition *) (data + 0x1be);



	disksig = le32_to_cpup((__le32 *)(data + 0x1b8));



	/*

	 * Look for partitions in two passes:

	 * First find the primary and DOS-type extended partitions.
@@ -515,11 +531,12 @@ int msdos_partition(struct parsed_partitions *state) 
			put_partition(state, slot, start, n);



			strlcat(state->pp_buf, " <", PAGE_SIZE);

			parse_extended(state, start, size);

			parse_extended(state, start, size, disksig);

			strlcat(state->pp_buf, " >", PAGE_SIZE);

			continue;

		}

		put_partition(state, slot, start, size);

		set_info(state, slot, disksig);

		if (SYS_IND(p) == LINUX_RAID_PARTITION)

			state->parts[slot].flags = ADDPART_FLAG_RAID;

		if (SYS_IND(p) == DM6_PARTITION)

init/do_mounts.c

+4 −0
Original line number Diff line number Diff line
@@ -189,6 +189,10 @@ done: 
 *	   used when disk name of partitioned disk ends on a digit.

 *	6) PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF representing the

 *	   unique id of a partition if the partition table provides it.

 *	   The UUID may be either an EFI/GPT UUID, or refer to an MSDOS

 *	   partition using the format SSSSSSSS-PP, where SSSSSSSS is a zero-

 *	   filled hex representation of the 32-bit "NT disk signature", and PP

 *	   is a zero-filled hex representation of the 1-based partition number.

 *	7) PARTUUID=<UUID>/PARTNROFF=<int> to select a partition in relation to

 *	   a partition with a known unique id.

 *

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