[Badmem-developer] Improved proc_memmap

[Yann D. <yd...@fr...>]

Hi,

I've worked a bit on memmap today, and discovered a couple of annoying
bugs, which I could fix, at the same time as I implemented a couple of
other things.  Here is the changelog:

 - extracted from badmem patch, and made so that both can be applied
   in any order
 - allowed to be used as a module to ease further development
 - fixed displayed offset for each line to be offset for this line,
   not next one's
 - fixed calculation of dotconst to include all requested pages
 - moved legend from /proc/memmap into Documentation/vm/memmap
 - added 'x' symbol to show pages below min_low_pfn
 - fixed error codes to be all negative, printk a message on all errors
 - protect write from buffer overflow
 - turned on auto-detection of numeration base of numbers written to
   procfile, instead of forcing 10
 - allow changing numbers of rows and columns


Note that allowing to build memmap as a module required that the
(min|max)_low_pfn symbols are exported from bootmem.c, which may not
be desirable.  I'm not digged much into the VM yet (memmap is supposed
to help me ;), but as I understand it, there should be after boottime
other means to get this information, which may already be exported.

However, it is infinitely more comfortable to be able to rmmod and
insmod a new version back for testing purposes.  I hope this will
encourage others to hack into this.

Other thoughts:

- writing to /proc/memmap is not much flexible.  We could want to add
more parameters to tune, or get other general information.  Maybe a
set of files in a /proc/memmap-params/ or so would be cleaner.

- a single view of the memory may not be flexible enough for some
uses.  It would be useful to keep an eye on the big picture while
looking at precise pieces of memory in a more precise manner.

That could probably be handled by a central writable file, to which we
would write things like "myregion 0 8000", resulting in
/proc/memmap/myregion being created to look at the specified region.

I thought it would be neat to be able to say just "echo 0 8000 >
/proc/memmap/myregion" to get that new map created, and "rm
/proc/memmap/myregion" to free the resources, but I fear procfs may
not be flexible enough for this.

Best regards,
-- 
Yann Dirson <Yan...@fr...>                 http://www.alcove.com/
Technical support manager                Responsable de l'assistance technique
Senior Free-Software Consultant          Consultant senior en Logiciels Libres
Debian developer (di...@de...)                        Développeur Debian