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

["Graham, Simon" <Simon.Graham@xxxxxxxxxxx>]

> Hi, Simon
> 
> >Two things:
> >
> >1. I'm not convinced 'xm crash' is needed - 'xm destroy' will do this
> >(and if you want
> >   a dump, do 'xm dump' followed by 'xm destroy')
> >
> What do you mean?
> I think we cannot dump with "xm destroy" now.
> "xm destory" only call the following domain_kill().

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.

> >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

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.

/simgr


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