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: Stephen Warren <swarren@nvidia.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Tejun Heo <tj@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/block/partitions/msdos.c b/block/partitions/msdos.c
index 5f79a6677c69706cee48844f2babd988fb5e26a8..8752a5d265653a5a743c333c9c99bb259aca554b 100644 (file)
--- 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, &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)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index fcbe8253645576137e92366f783f49a116f8b938..b6aa6324502f23a8c24cd738c472bd0ecc358723 100644 (file)
--- 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.
  *