Repair /proc/devices early-termination regression.

2.6.16 broke /proc/devices.  An application often gets an
EOF before the end of data is reached, if that application
uses a series of short read(2)s to access the data.  I have
used read buffers of varying sizes with varying degrees
of unsuccess (larger sizes get further into the data than
smaller sizes, following a simple pattern).  It appears
that the only safe way to get the data is to use a single
read buffer larger than all the data in /proc/devices.

The following example demonstates the problem:

    # dd if=/proc/devices bs=1
    Character devices:
      1 mem
    27+0 records in
    27+0 records out

This patch is a backport of the fix recently accepted to
Linus's tree:

    commit 68eef3b4791572ecb70249c7fb145bb3742dd899
    [PATCH] Simplify proc/devices and fix early termination regression

It replaces the complex, state-machine algorithm introduced
in 2.6.16 with a simple algorithm, modeled on the implementation
of /proc/interrupts.

[akpm@osdl.org: cleanups, simplifications]

Signed-off-by: Joe Korty <joe.korty@ccur.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

A Christoph suggested that the /proc/devices file be converted to use the
seq_file interface.  This patch does that.

I've obxerved one or two installation that had sufficiently large sans that
they overran the 4k limit on /proc/devices.

Signed-off-by: Neil Horman <nhorman@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Leave the overloaded "hotplug" word to susbsystems which are handling
real devices. The driver core does not "plug" anything, it just exports
the state to userspace and generates events.

Signed-off-by: Kay Sievers <kay.sievers@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Use the symbolic name where appropriate and add a comment to the
disk_stats structure.

Signed-off-by: Jens Axboe <axboe@suse.de>

drivers/block/ is right now a mix of core and driver parts. Lets move
the core parts to a new top level directory. Al will move the fs/
related block parts to block/ next.

Signed-off-by: Jens Axboe <axboe@suse.de>