UBI: R/O block driver on top of UBI volumes
This commit introduces read-only block device emulation on top of UBI volumes.
Given UBI takes care of wear leveling and bad block management it's possible
to add a thin layer to enable block device access to UBI volumes.
This allows to use a block-oriented filesystem on a flash device.
The UBI block devices are meant to be used in conjunction with any
regular, block-oriented file system (e.g. ext4), although it's primarily
targeted at read-only file systems, such as squashfs.
Block devices are created upon user request through new ioctls:
UBI_IOCVOLATTBLK to attach and UBI_IOCVOLDETBLK to detach.
Also, a new UBI module parameter is added 'ubi.block'. This parameter is
needed in order to attach a block device on boot-up time, allowing to
mount the rootfs on a ubiblock device.
For instance, you could have these kernel parameters:
ubi.mtd=5 ubi.block=0,0 root=/dev/ubiblock0_0
Or, if you compile ubi as a module:
$ modprobe ubi mtd=/dev/mtd5 block=/dev/ubi0_0
Artem: amend commentaries and massage the patch a little bit.
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
diff --git a/include/uapi/mtd/ubi-user.h b/include/uapi/mtd/ubi-user.h
index 723c324..b98585a 100644
--- a/include/uapi/mtd/ubi-user.h
+++ b/include/uapi/mtd/ubi-user.h
@@ -134,6 +134,13 @@
* used. A pointer to a &struct ubi_set_vol_prop_req object is expected to be
* passed. The object describes which property should be set, and to which value
* it should be set.
+ *
+ * Block devices on UBI volumes
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * To attach or detach a block device from an UBI volume the %UBI_IOCVOLATTBLK
+ * and %UBI_IOCVOLDETBLK ioctl commands should be used, respectively.
+ * These commands take no arguments.
*/
/*
@@ -191,6 +198,10 @@
/* Set an UBI volume property */
#define UBI_IOCSETVOLPROP _IOW(UBI_VOL_IOC_MAGIC, 6, \
struct ubi_set_vol_prop_req)
+/* Attach a block device to an UBI volume */
+#define UBI_IOCVOLATTBLK _IO(UBI_VOL_IOC_MAGIC, 7)
+/* Detach a block device from an UBI volume */
+#define UBI_IOCVOLDETBLK _IO(UBI_VOL_IOC_MAGIC, 8)
/* Maximum MTD device name length supported by UBI */
#define MAX_UBI_MTD_NAME_LEN 127