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, 4 insertions, 0 deletions

diff --git a/init/do_mounts.c b/init/do_mounts.c
index c950d7c93f98..1d1b6348f903 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.
  *