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

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@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?