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tianon / docker-qemu

Dockerization of supported QEMU releases
https://qemu.org
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Need more accurate test on /dev/kvm #4

Closed infinnovation-dev closed 3 years ago

infinnovation-dev commented 5 years ago

If running as a non-privileged user, e.g. using singularity or (untested) podman rather than docker, and /dev/kvm has restricted permissions, the test on the existence of /dev/kvm may lead start-qemu to set the -enable-kvm flag which then doesn't work. Perhaps

if [ -r /dev/kvm ]; then

would be better?

tianon commented 4 years ago

I agree a more robust test would be great -- my only concern is that we need to also ensure the test ensures our cgroup has access, which I think is possibly harder than just test -r? (not sure)

tianon commented 3 years ago

Just to come back and confirm my suspicions here:

$ docker run --rm -v /dev/kvm:/kvm:ro bash test -w /kvm; echo $?
0

(Both test -r and test -w are insufficient :disappointed:)

tianon commented 3 years ago

Here's an idea that might work, but I have no idea how abusive this is to this kernel interface: :weary:

$ docker run --rm -v /dev/kvm:/kvm bash -c 'echo -n > /kvm'; echo $?
bash: line 1: /kvm: Operation not permitted
1
$ docker run --rm --device /dev/kvm:/kvm bash -c 'echo -n > /kvm'; echo $?
0
tianon commented 3 years ago

Reading through https://lwn.net/Articles/658511/, this seems pretty sane -- thanks for filing the issue, and sorry it took me so long to find a better solution! :sweat_smile: