On 08.08.2016 09:33, Patrick PICHON wrote: > Hello, > > > All my VMs are using LVs created on the host side. > > I'm using collectd to monitor some of the ressources of my host as > well > as the libvirt pluging to monitor my VMs. > > Collectd has an interesting plugin ( df ) which can monitor the > filesystem usage. > > I would like to use it to monitor the VMs filesytsem usage. > > As it is obvious that if I mount the VM filesystem on the host while > the > VM is running, I'm wondering if I could mount it in READONLY without > expecting any panic/corruption problem. > > > Any advices ? I don't think it is a good idea. Mostly because of caching - you probably won't get consistent results. Moreover, some filesystems (e.g. ext4) replay journal even if mounted as RO (frankly, I haven't found a way how to mount ext really RO). I don't know of any filesystem that would support being mounted multiple times from two different hosts (except network FS obviously). What you could do is to write small guest agent that will report disk usage to host (e.g. via virito serial console). Michal

On 08.08.2016 09:33, Patrick PICHON wrote: > Hello, > > > All my VMs are using LVs created on the host side. > > I'm using collectd to monitor some of the ressources of my host as > well > as the libvirt pluging to monitor my VMs. > > Collectd has an interesting plugin ( df ) which can monitor the > filesystem usage. > > I would like to use it to monitor the VMs filesytsem usage. > > As it is obvious that if I mount the VM filesystem on the host while > the > VM is running, I'm wondering if I could mount it in READONLY without > expecting any panic/corruption problem. > > > Any advices ? I don't think it is a good idea. Mostly because of caching - you probably won't get consistent results. Moreover, some filesystems (e.g. ext4) replay journal even if mounted as RO (frankly, I haven't found a way how to mount ext really RO). I don't know of any filesystem that would support being mounted multiple times from two different hosts (except network FS obviously). What you could do is to write small guest agent that will report disk usage to host (e.g. via virito serial console). Michal _______________________________________________ libvirt-users mailing list libvirt-users(a)redhat.com https://www.redhat.com/mailman/listinfo/libvirt-users

On 08.08.2016 10:23, Patrick PICHON wrote: >  > hello Michal, >  > That was my worries as well, and I think that your advice is probably > the right one. Or even, I'm might request an enhancement to the collect > libvirt plugin to report also FS information.   What I'd like to see is libvirt's ability to spawn commands inside guest. But it is not that simple. I mean, the hardest part is to design public libvirt API. For instance, we'd have to deal with both blocking & non-blocking (i.e. long-running) commands; then we would need to give users possibility to read command's output (possibly asynchronously).   With this, you'd just: virDomainRunCommand(dom, 'df', '-h', NULL); or something and you'd be good.

On Mon, 2016-08-08 at 10:37 +0200, Michal Privoznik wrote: > On 08.08.2016 10:23, Patrick PICHON wrote: >> >> hello Michal, >> >> That was my worries as well, and I think that your advice is probably >> the right one. Or even, I'm might request an enhancement to the collect >> libvirt plugin to report also FS information. > > What I'd like to see is libvirt's ability to spawn commands inside > guest. But it is not that simple. I mean, the hardest part is to design > public libvirt API. For instance, we'd have to deal with both blocking & > non-blocking (i.e. long-running) commands; then we would need to give > users possibility to read command's output (possibly asynchronously). > > With this, you'd just: virDomainRunCommand(dom, 'df', '-h', NULL); or > something and you'd be good. Not as straightforward as you'd like, but if you use QEMU you can already achieve something similar via qemu-guest-agent. https://www.redhat.com/archives/libvir-list/2016-August/msg00339.html