Re: [libvirt] Some problem with the save function

Le mercredi 16 septembre 2009 à 21:36 +0100, Daniel P. Berrange a écrit : > On Wed, Sep 16, 2009 at 05:05:36PM +0200, Daniel Berteaud wrote: > > Hi everyone. This is my first post to this list, so excuse me if it's > > not the right place to poste info like this. > > > > I've found some problems in qemu_driver.c in the latest versions of > > libvirt: > > > > - the first problem was also present in 0.7.0. If we run qemu guests > > unprivileged, we cannot use the save function (virsh save > > guestname /path/to/file). The reason seems to be that libvirt first > > create the destination file to write the header and the XML definition. > > The file is owned by root with 600 permission. Then, we ask qemu to > > append the dump of the memory (via the migrate exec: call) to this file. > > This part doesn't work because the qemu user cannot write to this file. > > So we endup with a file which only contains the header and the XML, and > > the guest is stoped :/ > > Doh, that's a nice problem. You can work around it by editing > /etc/libvirt/qemu.conf and telling qemu to run as root:root > again. For a real fix we'll need to make the save method > run 'fchown' on the file descriptor after writing the header. > And then fchown it back to root:root once complete, to stop > any other guest overwriting it. As I only use the save function in a script, I work around it by touching the file and chowning it to qemu:qemu before calling save, I sleep better when my guests runs with less privileges ;) > > > - the second problem is present since libvirt 0.7.1. Now that the saved > > file can be compressed, it seems we cannot save in a raw format any > > more. This is due to this part in the code (qemu_driver.c): > > > > if (STREQ (prog, "raw")) > > prog = "cat"; > > internalret = virAsprintf(&command, "migrate \"exec:" > > "%s -c >> '%s' 2>/dev/null\"", prog, > > safe_path); > > > > which result in "migrate \"exec cat -c >> safe_path 2>/dev/null\"" > > > > But cat doesn't support the -c argument, so once again, the save fails, > > as we end up with a save file which only contains the header and the XML > > definition. > > Wierd, I don't know where/when we gained a '-c' arg to cat but it > looks rather bogus. The change is in this patch : http://libvirt.org/git/?p=libvirt.git;a=commit;h=aec22258ef01d7cf36b031a4... > > > - the third problem, is that restore doesn't work any more. I haven't > > dig it yet, but when I try to restore a guest using a saved file > > (uncompressed produced under libvirt 0.7.0), I've this error: > > > > virsh restore /tmp/guest.state > > error: Failed to restore domain from /tmp/guest.state > > error: internal error unable to start guest: > > Hmm, bad error message :-( We might also need todo a chown() > in the restore path to allow QEMU to read it. NB there is no > compatability between QEMU version, so if you have upgraded > your install of QEMU between the time you saved & restored > it is very likely to crash & burn. I haven't upgraded qemu, just libvirt. And I must admit that I don't really know where and how to debug it, I'm very new to libvirt ;) (and I really don't know anything in C) Would just like to know if someone could get it working in 0.7.1, or if there's a big bug somewhere in this release.