qemu: Add swtpm to emulator cgroup

qemu: Add swtpm to emulator cgroup

Add the external swtpm to the emulator cgroup so that upper limits of CPU
usage can be enforced on the emulated TPM.

To enable this we need to have the swtpm write its process id (pid) into a
file. We then read it from the file to configure the emulator cgroup.

The PID file is created in /var/run/libvirt/qemu/swtpm:

[root@localhost swtpm]# ls -lZ /var/run/libvirt/qemu/swtpm/
total 4
-rw-r--r--. 1 tss  tss  system_u:object_r:qemu_var_run_t:s0          5 Apr 10 12:26 1-testvm-swtpm.pid
srw-rw----. 1 qemu qemu system_u:object_r:svirt_image_t:s0:c597,c632 0 Apr 10 12:26 1-testvm-swtpm.sock

The swtpm command line now looks as follows:

root@localhost testvm]# ps auxZ | grep swtpm | grep socket | grep -v grep
system_u:system_r:virtd_t:s0:c597,c632 tss 18697 0.0  0.0 28172 3892 ?       Ss   16:46   0:00 /usr/bin/swtpm socket --daemon --ctrl type=unixio,path=/var/run/libvirt/qemu/swtpm/1-testvm-swtpm.sock,mode=0600 --tpmstate dir=/var/lib/libvirt/swtpm/485d0004-a48f-436a-8457-8a3b73e28568/tpm1.2/ --log file=/var/log/swtpm/libvirt/qemu/testvm-swtpm.log --pid file=/var/run/libvirt/qemu/swtpm/1-testvm-swtpm.pid

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>