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: 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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 19 insertions, 2 deletions

diff --git a/block/partitions/msdos.c b/block/partitions/msdos.c
index 5f79a6677c69..8752a5d26565 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, &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)