[PATCH] UBI: block: Configurable device major number

[Dan Ehrenberg]

By default UBI block devices use a dynamic major number. This
config option can replace that with a static major number. Set
to the new major number, or 0 for dynamic. This is useful if
you want to use an ubiblock as the root filesystem in an
indirect way, e.g., though DM and need to refer to it before
userspace is up.

Signed-off-by: Dan Ehrenberg <dehrenberg at chromium.org>
---
 drivers/mtd/ubi/Kconfig | 13 +++++++++++++
 drivers/mtd/ubi/block.c |  7 ++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index f0855ce..5ac8d63 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -103,4 +103,17 @@ config MTD_UBI_BLOCK
 
 	   If in doubt, say "N".
 
+config MTD_UBI_BLOCK_MAJOR
+	int "Major device number for UBI block devices"
+	default 0
+	range 0 256
+	depends on MTD_UBI_BLOCK
+	help
+	   By default UBI block devices use a dynamic major number. This
+	   config option can replace that with a static major number. Set
+	   to the new major number, or 0 for dynamic. This is useful if
+	   you want to use an ubiblock as the root filesystem in an
+	   indirect way, e.g., though DM and need to refer to it before
+	   userspace is up.
+
 endif # MTD_UBI
diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
index 6b6bce2..6c8333d 100644
--- a/drivers/mtd/ubi/block.c
+++ b/drivers/mtd/ubi/block.c
@@ -635,9 +635,14 @@ int __init ubiblock_init(void)
 {
 	int ret;
 
-	ubiblock_major = register_blkdev(0, "ubiblock");
+	ubiblock_major = register_blkdev(CONFIG_MTD_UBI_BLOCK_MAJOR,
+					 "ubiblock");
 	if (ubiblock_major < 0)
 		return ubiblock_major;
+	if (CONFIG_MTD_UBI_BLOCK_MAJOR) {
+		BUG_ON(ubiblock_major);
+		ubiblock_major = CONFIG_MTD_UBI_BLOCK_MAJOR;
+	}
 
 	/* Attach block devices from 'block=' module param */
 	ret = ubiblock_create_from_param();
-- 
2.2.0.rc0.207.ga3a616c