[Crash-utility] PATCH 00/10] teach crash to work with "live" ramdump

[Oleg Nesterov]

On 04/26, Dave Anderson wrote:
>
>
> ----- Original Message -----
> > On 04/26, Dave Anderson wrote:
> > >
> > > > No, just a regular file, qemu creates it and does mmap(MAP_SHARED) on it.
> > > >
> > > > > that constantly contains the
> > > > > current contents of the guest's physical memory?
> > > >
> > > > Yes,
> > > >
> > > > > Is it like /dev/mem?
> > > >
> > > > yes, but more like /dev/crash.
> > > >
> > > > Oleg.
> > >
> > > Unfortunately I am completely unfamiliar with qemu option specifications.
> >
> > I too do not know much about qemu options,
> >
> > > So if I were to log into the guest machine, does a /tmp/MEM file exist?
> >
> > No,
> >
> > > Or does it exist on the host machine?
> >
> > Yes, it is just the normal file on the host which runs qemu.
> >
> > Well, "normal" is not neccessarily true in that you can use, for example,
> >
> > 	mem-path=/path/to/hugetlb-mount/...
> >
> > but this doesn't matter. It is still the "regular" file mmaped by qemu, the
> > host can read it to acess the guest's physical memory.
> >
> > Oleg.
>
> OK, so we're running on a host machine that has one of these memory files
> that is accessible as a regular file.

Yes, and this file is the physical memory of the guest. So it is essentially
the RAM dump which can be used by "crash PATH-TO-THIS-FILE at 0" right now without
any patches. And in this particular case the offset is always zero.

But not on x86-64, is_ramdump() insists on ramdump_to_elf() even if we could
use read_ramdump(), and ramdump_to_elf() doesn't support x86-64.

And of course, you can't use this RAM dump in "live" mode (without these
changes).

> So what's the remote access needed
> for -- just to query for the particulars of the layout of the memory file?

Sorry, I don't understand...

Do you ask me what qemu does with this file or what?

Oleg.