Re: [libvirt] [PATCH v1 0/4] libxl: channels support

On 20.09.2016 12:43, Joao Martins wrote: > On 09/20/2016 05:14 AM, Michal Privoznik wrote: >> On 20.09.2016 00:04, Jim Fehlig wrote: >>> On 09/16/2016 05:43 PM, Joao Martins wrote: >>>> Hey, >>>> >>>> Additionally what does "state" >>>> signify for virtio case: is it that the guest agent is connected, or that the >>>> virtio serial is connected? Looking at the qemu driver on >>>> processSerialChangedEvent it sounds to me like it's about the serial state. >>> >>> AFAICT you are right, but perhaps Michal is kind enough to confirm. I think he >>> is familiar with this code. >> >> That attribute is put by libvirt into live XML so that mgmt apps can >> query for it. The attribute says whether the guest part of channel is >> opened by a process running within guest. In case of the qemu-ga whether >> we have the guest agent up & running. Whenever the guest end of a >> channel is opened/closed, qemu sends us an event so we can update our >> internal state and put the correct value when formatting live XML. >> Therefore, it makes no sense to make this attribute RW (meaning users >> could set it), obviously. > Hmm if it refers to qemu agent actually (dis)connected from guest side it might > be difficult to provide the same "state" semantics in libxl driver at least > without changes on the toolstack. If it referring to virtio-serial state we > could easily do that by periodically calling libxl_channel_getinfo until state > is 4 (connected). But it's the actual agent process state as connected in which > case to have "state" attribute we would need to add similar to libxl event > DOMAIN_CREATE_CONSOLE_AVAILABLE but instead referring to the guest channel. Well, in qemu it really just means that somebody is listening. Note that I say "somebody". That is if you kill qemu-ga in the guest and just 'cat /dev/virtio-ports/org.qemu-ga.' we will report state='connected' (or what's the path, and yes you can't use cat, but you get my point).

We don't do any checks whether it is actual qemu-ga listening. Moreover, we report that for all the channels, not just the one used by the guest agent. So it really means that there is somebody listening in the guest.