[Crash-utility] dev command deteriorates with new kernels

[Bob Montgomery]

On Mon, 2009-06-08 at 19:50 +0000, Dave Anderson wrote:

Regarding blkext 259
> 
> Correction -- it does appear in the major_names[] array, in a 2.6.30
> kernel for example, like this:
> 
>   crash> p * major_names[4]
>   $51 = {
>     next = 0x0, 
>     major = 259, 
>     name = "blkext\000\000\000\000\000\000\000\000\000"
>   }
> 
> where it appears to be the only major_names[] entry whose "major" value
> doesn't equal the index into the array (i.e., 259 != 4).  But the
> bdev_map.probes[4] entry is unused.

The blkext is supposed to get used as soon as someone wants to put more
than 15 partitions on an sd disk.  (Explanation at
http://thread.gmane.org/gmane.linux.kernel/701825)

Then the upper partitions will appear as minors of 259.  When that
starts happening more, having a way to see it might (*might*) be
interesting.

> > At this point I'm about ready to deprecate the whole command...  ;-)

And at this point I couldn't really argue much :-)  I obviously hadn't
used the command for a while.  I was casting around, hoping it would
maybe help me find the diskstats stuff for the block devices.  I was
trying to answer a question like "How much disk activity was going on
before this crashed?"

When I tried the dev command and it bombed at the chrdev stuff before
getting to the blkdev stuff, I was motivated to get it going enough to
see if it would help answer my question, but it doesn't print anything
(like hd_struct pointers) that could help me with my problem.  But I
figured someone had once wanted that device info, so it might as well
work...

Bob Montgomery