The "bdev" library provides basic primitives for file systems to talk
to block device drivers, hiding the details of the underlying protocol
and interaction model.
This version of libbdev is rather basic. It is planned to support the
following features in the long run:
- asynchronous requests and replies;
- recovery support for underlying block drivers;
- retrying of failed I/O requests.
The commit also changes our block-based file systems (mfs, ext2, isofs)
to make use of libbdev.
. move cache size heuristic from mfs there
so mfs and ext2 can share it
. add vfs credentials retrieving function, with
backwards compatability from previous struct
format, to be used by both ext2 and mfs
. fix for ext2 - STATICINIT was fed no.
of bytes instead of no. of elements, overallocating
memory by a megabyte or two for the superblock
