----- Original Message ----- > On 04/26, Dave Anderson wrote: > > > > I didn't write this code, but here's how I understand it. > > Thanks Dave, I'll read your explanation tomorrow, I need to run away again. > > > > OK. So I am running the rhel7 guest on my Fedora machine and I pass the following > > > (additional) options to qemu: > > > > > > -object memory-backend-file,id=MEM,size=128m,mem-path=/tmp/MEM,share=on \ > > > -numa node,memdev=MEM \ > > > > > > so in this (trivial) case /tmp/MEM represents the physical memory as it seen by > > > the guest. > > > > Exactly what is this /tmp/MEM that you speak of? > > please note the "mem-path=/tmp/MEM" in the memory-backend-file arg above. > > With this option qemu doesn't use the anonymous/private mapping for the guest's > physical memory it creates a file (specified by mem-path=). The host can read > (and write of course) to this file. This file _is_ the guest's physical memory. > > Just in case, you pass multiple memory-backend-file/numa arguments, so you will > have the "multi-file" ramdump. > > > > Now suppose that this guest crashes and qemu exits. In this case the "live" mode > > > makes no sense, if nothing else it is slower. > > > > I don't understand. Does the /tmp/MEM file still exist somewhere after the guest > > crashed? > > Yes, > > > > > > "live" ramdump is a bit more interesting. I can do > > > > > > $ crash path-to-rhel7-vmlinux live:/tmp/MEM@0 > > > > Again, I am clueless as to what /tmp/MEM consists of on the guest. > > See above, > > > Is is a pseudo-file > > 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. So if I were to log into the guest machine, does a /tmp/MEM file exist? Or does it exist on the host machine? Dave -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
