blk: blkmap: Add basic infrastructure

blkmaps are loosely modeled on Linux's device mapper subsystem. The
basic idea is that you can create virtual block devices whose blocks
can be backed by a plethora of sources that are user configurable.

This change just adds the basic infrastructure for creating and
removing blkmap devices. Subsequent changes will extend this to add
support for actual mappings.

Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index e95da48bdc0..5a1aeb3d2b4 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -67,6 +67,24 @@ config BLOCK_CACHE
 	  it will prevent repeated reads from directory structures and other
 	  filesystem data structures.
 
+config BLKMAP
+	bool "Composable virtual block devices (blkmap)"
+	depends on BLK
+	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 SPL_BLOCK_CACHE
 	bool "Use block device cache in SPL"
 	depends on SPL_BLK