cmd: blkmap: Add blkmap command

Add a frontend for the blkmap subsystem. In addition to the common
block device operations, this allows users to create and destroy
devices, and map in memory and slices of other block devices.

With that we support two primary use-cases:

- Being able to "distro boot" from a RAM disk. I.e., from an image
  where the kernel is stored in /boot of some filesystem supported
  by U-Boot.

- Accessing filesystems not located on exact partition boundaries,
  e.g. when a filesystem image is wrapped in an FIT image and stored
  in a disk partition.

Signed-off-by: Tobias Waldekranz <[email protected]>
Reviewed-by: Simon Glass <[email protected]>

1 files changed, 19 insertions, 0 deletions

diff --git a/cmd/Kconfig b/cmd/Kconfig
index 8c9b430f99f..bab35fc6678 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1980,6 +1980,25 @@ config CMD_BLOCK_CACHE
 	  during development, but also allows the cache to be disabled when
 	  it might hurt performance (e.g. when using the ums command).
 
+config CMD_BLKMAP
+	bool "blkmap - Composable virtual block devices"
+	depends on BLKMAP
+	default y if BLKMAP
+	help
+ 	  Create virtual block devices that are backed by various sources,
+ 	  e.g. RAM, or parts of an existing block device. Though much more
+ 	  rudimentary, it borrows a lot of ideas from Linux's device mapper
+ 	  subsystem.
+
+	  Example use-cases:
+	  - Treat a region of RAM as a block device, i.e. a RAM disk. This let's
+            you extract files from filesystem images stored in RAM (perhaps as a
+            result of a TFTP transfer).
+	  - Create a virtual partition on an existing device. This let's you
+            access filesystems that aren't stored at an exact partition
+            boundary. A common example is a filesystem image embedded in an FIT
+            image.
+
 config CMD_BUTTON
 	bool "button"
 	depends on BUTTON