DTrace (or other monitor) access to LBA of a block device

[Artem Belevich]

> GEOM sounds like a good candidate for probing of that kind.
>
> sudo dtrace -n 'fbt:kernel:g_io_deliver:entry { printf("%s %d %d
> %d\n",stringof(args[0]->bio_from->geom->name), args[0]->bio_cmd,
> args[0]->bio_offset, args[0]->bio_length); }'

By the way, in order for this to work one would need r207057 applied
to -8. Any chance that could be MFC'ed?

http://svn.freebsd.org/viewvc/base?view=revision&revision=207057

--Artem