[PATCH] UBI: new module ubiblk: block layer on top of UBI

[Christoph Hellwig]

> TODO:
>  * the modules keeps a table of the devices which length is the maximum number
>    of UBI volumes.  It should make use of a linked list.

A linked list isn't very nice either.  Try using idr, which gives you
both an allocator for the minor number space, and a way to look up
the structure by that index.

> Advantages of ubiblk over gluebi+mtdblock_ro:

This section should be in the main commit log, and not that part with
the changelog which gets dropped.

> +int major;

Please don't use global variables with generic names.  In this case you
should neither make it global nor give it a generic name.