From: Stephen Warren swarren@nvidia.com
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: Stephen Warren swarren@nvidia.com --- block/partitions/msdos.c | 21 +++++++++++++++++++-- init/do_mounts.c | 4 ++++ 2 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/block/partitions/msdos.c b/block/partitions/msdos.c index 5f79a66..8752a5d 100644 --- a/block/partitions/msdos.c +++ b/block/partitions/msdos.c @@ -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, §); 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) diff --git a/init/do_mounts.c b/init/do_mounts.c index fcbe825..b6aa632 100644 --- a/init/do_mounts.c +++ b/init/do_mounts.c @@ -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. *