Re: [PATCH] kmem, snap: iomem/ioport display and vmcore snapshot support

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----- Original Message -----
> From: Dave Anderson <anderson@xxxxxxxxxx>
> Subject: Re:  [PATCH] kmem, snap: iomem/ioport display
> and vmcore snapshot support
> Date: Tue, 13 Mar 2012 10:17:20 -0400 (EDT)
> 
> > 
> > 
> > ----- Original Message -----
> >> Some days ago I was in a situation that I had to convert vmcore in
> >> kvmdump format into ELF since some extension module we have locally
> >> can be used only on relatively old crash utility, around version 4,
> >> but such old crash utility cannot handle kvmdump format.
> > 
> > That's a pretty weak argument -- what did crash version ~4 have
> > that the latest version does not?  I don't recall ever removing
> > any functionality w/respect to extension module without replacing
> > it with a better interface.  In other words, why can't you fix your
> > local extension module?  I need a better reason for modifying
> > the snap module other than that.
> > 
> 
> I don't know the detail of the local extension module. The man who
> requested a help to me explained that his module gets information of
> vmcore using crash (gdb) scripts and retrives values from the scripts'
> output via pipe. While old crash behaves well, recent ones appear to
> hang in the situation where both reading and writing sides wait each
> other. Is there any difference of behaviour on communication with
> gdb?

I don't know exactly.  There's certainly have been new gdb versions,
and the changelog has a few small patches w/respect to gdb commands,
but it's hard to say how they might affect the usage of gdb scripts
from a module (?).  

> 
> Anyway it's natural that we should modify the extension module, and
> we'll do that soon. The patch for snap command was a workaround, but
> there's merit to the patch that it makes it possible to use it as
> handy vmcore conversion tool, not just as live kernel dump command, so
> I've posted this here. By this, snap command will become able to
> convert all the format currently crash supports into ELF. Though I
> have yet to test this, this can convert lkcd foramt into ELF, for
> example. Someone might want to use this for vmcore not suppoted by
> Makedumpfile.

OK, here's what to do.  The snap extension module is just that -- it
takes a "snapshot" of live physical memory and creates an ELF file.
I don't want to change that.

However, I suppose the concept of a "conversion-to-ELF" tool makes sense.
That being the case, please create a standalone extension module, and 
call it "mkelf", or "kvm2elf", or whatever name you want.  Then we can
add it to the collection of modules on the extension module web page.

Thanks,
  Dave

> 
> > 
> > Why reinvent the wheel?  The "dev -i" command does all of the above, plus
> > gives you the resource structure address:
> >  
> >   crash> dev -i
> >       RESOURCE        RANGE    NAME
> >   ffffffff80312080  0000-ffff  PCI IO
> <cut>
> 
> I myself thought it's strange if it's not present. Before making my
> patch, I did minimum check by searching crash source code for related
> symbols such as ``resource'', but I didn't find anything. Now I see
> some symbols found with the same keyword. I think I did something
> wrong at that time.
> 
> Thanks.
> HATAYAMA, Daisuke
> 
> 

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