cmd: Add MBR partition layout control utility

Add a 'mbr' command to let users create or verify MBR partition layout
based on the provided text description. The partition layout is
alternatively read from the 'mbr_parts' environment variable. This can be
used in scripts to help system image flashing tools to ensure proper
partition layout.

The syntax of the text description of the partition list is similar to
the one used by the 'gpt' command. Supported parameters are: name
(currently ignored), start (partition start offset in bytes), size (in
bytes or '-' to expand it to the whole free area), bootable (boolean
flag) and id (MBR partition type). If one wants to create more than 4
partitions, an 'Extended' primary partition (with 0x05 ID) has to be
explicitely provided as a one of the first 4 entries.

Here is an example how to create a 6 partitions (3 on the 'extended
volume'), some of the predefined sizes:

> setenv mbr_parts 'name=boot,start=4M,size=128M,bootable,id=0x0e;
  name=rootfs,size=3072M,id=0x83;
  name=system-data,size=512M,id=0x83;
  name=[ext],size=-,id=0x05;
  name=user,size=-,id=0x83;
  name=modules,size=100M,id=0x83;
  name=ramdisk,size=8M,id=0x83'
> mbr write mmc 0

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

2 files changed, 95 insertions, 0 deletions

diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index fbb2c0481c..5869fba189 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -14,4 +14,5 @@ Shell commands
    bootefi
    bootmenu
    button
+   mbr
    pstore
diff --git a/doc/usage/mbr.rst b/doc/usage/mbr.rst
new file mode 100644
index 0000000000..bddf2f612a
--- /dev/null
+++ b/doc/usage/mbr.rst
@@ -0,0 +1,94 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+mbr command
+===========
+
+Synopsis
+--------
+
+::
+
+    mbr verify [interface] [device no] [partition list]
+    mbr write [interface] [device no] [partition list]
+
+Description
+-----------
+
+The mbr command lets users create or verify the MBR (Master Boot Record)
+partition layout based on the provided text description. The partition
+layout is alternatively read from the 'mbr_parts' environment variable.
+This can be used in scripts to help system image flashing tools to ensure
+proper partition layout.
+
+The syntax of the text description of the partition list is similar to
+the one used by the 'gpt' command.
+
+Supported partition parameters are:
+
+* name (currently ignored)
+* start (partition start offset in bytes)
+* size (in bytes or '-' to expand it to the whole free area)
+* bootable (boolean flag)
+* id (MBR partition type)
+
+If one wants to create more than 4 partitions, an 'Extended' primary
+partition (with 0x05 ID) has to be explicitly provided as a one of the
+first 4 entries.
+
+Here is an example how to create a 6 partitions (3 on the 'extended
+volume'), some of the predefined sizes:
+
+::
+
+    => setenv mbr_parts 'name=boot,start=4M,size=128M,bootable,id=0x0e;
+        name=rootfs,size=3072M,id=0x83;
+        name=system-data,size=512M,id=0x83;
+        name=[ext],size=-,id=0x05;
+        name=user,size=-,id=0x83;
+        name=modules,size=100M,id=0x83;
+        name=ramdisk,size=8M,id=0x83'
+    => mbr write mmc 0
+
+To check if the layout on the MMC #0 storage device matches the provided
+text description one has to issue following command (assuming that
+mbr_parts environment variable is set):
+
+::
+
+    => mbr verify mmc 0
+
+The verify sub-command is especially useful in the system update scripts:
+
+::
+
+    => if mbr verify mmc 0; then
+         echo MBR layout needs to be updated
+         ...
+       fi
+
+The 'mbr write' command returns 0 on success write or 1 on failure.
+
+The 'mbr verify' returns 0 if the layout matches the one on the storage
+device or 1 if not.
+
+Configuration
+-------------
+
+To use the mbr command you must specify CONFIG_CMD_MBR=y.
+
+Return value
+------------
+
+The variable *$?* takes the following values
+
++---+------------------------------+
+| 0 | mbr write was succesful      |
++---+------------------------------+
+| 1 | mbr write failed             |
++---+------------------------------+
+| 0 | mbr verify was succesful     |
++---+------------------------------+
+| 1 | mbr verify was not succesful |
++---+------------------------------+
+|-1 | invalid arguments            |
++---+------------------------------+