On Fri, Aug 17, 2012 at 08:10:40AM -0500, Ryan Harper wrote:
- Dan Kenigsberg danken@redhat.com [2012-08-16 15:59]:
On Thu, Aug 16, 2012 at 10:53:17AM -0500, Ryan Harper wrote:
- Dan Kenigsberg danken@redhat.com [2012-08-16 03:37]:
Dan Kenigsberg has posted comments on this change.
Change subject: Fix vdsm-faqemu VM launch failure on hosts with newer libvirt ......................................................................
Patch Set 1: I would prefer that you didn't submit this
(1 inline comment)
.................................................... File vdsm_hooks/faqemu/vdsm-faqemu Line 20: Line 21: qemu_argv += filter(lambda x: x != "-enable-kvm", sys.argv[1:]) Line 22: # libvirt 0.9.10+ checks for the presence of /dev/kvm to provide Line 23: # better error messages, but this breaks this hook, fake it out Line 24: os.system("touch /dev/kvm") how can this work? this script runs as vdsm.
# sudo -u vdsm touch /dev/kvm touch: cannot touch `/dev/kvm': Permission denied
But I can assure you that it did work. I didn't just touch the file as root. I installed the faqemu hook and /dev/kvm is owned by root. Are you sure hooks run as vdsm?
Yes. They are called by hooks.py's execCmd. However I was wrong about this script being a hook script: it is the emulator used by libvirt instead of qemu. Again, I am very much surprised that this runs as root - libvirt's default is qemu:qemu.
Agreed, I'm not quite sure what's going on here as the VMs indeed are running as non-root qemu user:
Could libvirt be running the emulator twice? Once as root to check -help, and then as qemu?
qemu 31698 2.0 0.8 997456 71884 ? Sl Aug16 25:45 /usr/bin/qemu-kvm
It's run as root:
[root@ichigo-dom228 tmp]# cat /usr/libexec/vdsm/vdsm-faqemu #!/usr/bin/python
import os import sys
qemu_paths = [ "/usr/bin/qemu-kvm", "/usr/libexec/qemu-kvm", ]
for qemu_bin in qemu_paths: if os.path.exists(qemu_bin): break else: raise RuntimeError, "QEMU binary not found"
qemu_argv = [ qemu_bin ]
if not "-no-kvm" in sys.argv: qemu_argv += [ "-no-kvm" ]
qemu_argv += filter(lambda x: x != "-enable-kvm", sys.argv[1:]) os.system('id > /tmp/faqemu_id.out') os.system('touch /dev/kvm') os.execv(qemu_bin, qemu_argv)
[root@ichigo-dom228 tmp]# cat /tmp/faqemu_id.out uid=0(root) gid=0(root) groups=0(root) context=system_u:system_r:virtd_t:s0-s0:c0.c1023
also, there are less expensive ways to create a file - how about shipping it in this hook's rpm ?
Is that really less expensive? I worry about having an rpm include the file; and /dev gets remounted/changed accross reboots; so this wouldn't work.
What's expensive about a touch?
It is, comparing to opening the file for writing
file('/dev/kvm', 'w')
We're launching a VM, an additional exec isn't a lot of overhead. If someone comes back and says launching the VM took too long and we spend all our time in one os.system('touch') call, then maybe you're right.
(platechiller) ~ % cat touch.py import os os.system('touch /dev/kvm') (platechiller) ~ % sudo time python touch.py 0.01user 0.00system 0:00.01elapsed 84%CPU (0avgtext+0avgdata 21328maxresident)k 0inputs+0outputs (0major+2424minor)pagefaults 0swaps
Yes, one fork is negligible. But they pile up. I see no reason to call fork(2) when you actually want open(2).
Anyway, I cannot say that I'm happy with this solution: nothing clears /dev/kvm after the hook is uninstalled, for one's.
/dev/kvm will be removed on reboot since /dev is reconstructed.
The presence of the file doesn't bother loading of the module either:
(platechiller) ~ % ls -al /dev/kvm crw-rw----+ 1 root kvm 10, 232 Aug 17 08:06 /dev/kvm (platechiller) ~ % sudo modprobe -vr kvm_intel kvm rmmod /lib/modules/3.2.0-29-generic/kernel/arch/x86/kvm/kvm-intel.ko rmmod /lib/modules/3.2.0-29-generic/kernel/arch/x86/kvm/kvm.ko (platechiller) ~ % ls -al /dev/kvm ls: cannot access /dev/kvm: No such file or directory (platechiller) ~ % sudo touch /dev/kvm (platechiller) ~ % ls -al /dev/kvm -rw-r--r-- 1 root root 0 Aug 17 08:06 /dev/kvm (platechiller) ~ % sudo modprobe -v kvm-intel insmod /lib/modules/3.2.0-29-generic/kernel/arch/x86/kvm/kvm.ko insmod /lib/modules/3.2.0-29-generic/kernel/arch/x86/kvm/kvm-intel.ko (platechiller) ~ % ls -al /dev/kvm crw-rw----+ 1 root kvm 10, 232 Aug 17 08:07 /dev/kvm
It's less destructive than I thought, but it's not prettier... On the other hand, it let's touch the file only when the script is enabled.
Dan.