RE: [Patch][RFC] Support "xm dump" (is Re:Re:[Patch]Enable "sysrq c" handler for domU coredump)

[Akio Takebe <takebe_akio@jp.fujitsu.com>]

Hi, Simon

>I mean that if you want to crash a domain and collect a dump, you can do
>'xm dump' followed by 'xm destroy' or 'xm reboot' -- there's no need to 
>add another command to do the combination.
OK, I understand.

>> >2. I don't see the point of the --noreboot option on 'xm dump' -- I
>> >think this command
>> >   should simply live-dump the specified domain - as above you can
>use
>> >other commands
>> >   to cause the domain to restart afterwards.
>> >
>> Ordinary dump features have atomatically rebooting features.
>> (e.g. diskdump, kdump, and so on)
>> So I think this is necessary.
>
>xm dump foo
>xm reboot foo
OK.

>
>does the job nicely -- why complicate things by adding extra
>options/commands
>
>> 
>> >3. There's no need to pause the domain to dump it - I actually wrote
>a
>> >little utility
>> >   to live dump a guest (based on xenconsoled and attached) and it
>> seems
>> >to work
>> >   quite nicely! This could easily be morphed into the 'xm dump'
>> command
>> >- it just
>> >   didn't occur to me at the time!
>> >
>> Your xendump command is dump feature without pause.
>> In the case without pause, domain's memory is modified while dumping.
>> I think both w/o and w pause are needed.
>
>Hmm... perhaps although I'm not convinced -- I understand that memory
>can change during the dump and therefore there can be some
>inconsistencies in the dump, HOWEVER, pausing the domain doesn't ensure
>all the data structures are consistent either - it pretty much just
>stops the VM wherever is happens to be so the memory can still be
>inconsistent. 
>
>I also think there is an issue with pausing -- unless I am mistaken,
>pause requires code to run in the domain - if the domain is glued up
>this cant run and the pause will hang (and lets face it, the usual
>reason for dumping a domain is because something is wrong; definitely a
>good idea to minimize the amount of work you expect from the domain in
>this case).
>
>FWIW, my opinion is that it isn't necessary to pause.
>
I don't agree it. It is necessary to pause for dumping domU's core,
because debugging is difficut with the unpause core.

But I think we can resolve the issue with the following way.
- If we want to get dump with pause
  1. xm pause foo
  2. xm dump foo
  3. xm reboot foo (if want to reboot)

- If we want to get live dump w/o pause
  1. xm dump foo

BTW, I try to make your xendump.c, but cannot compile it.
Could you post the Makefile?
I'd like to use your xendump.

Best Regards,

Akio Takebe