Greetings Peter,
> Sent: Monday, January 07, 2019 at 11:06 AM
> From: "Peter Krempa" <pkre...@redhat.com>
> To: daggs <da...@gmx.com>
> Cc: libvirt-users@redhat.com
> Subject: Re: [libvirt-users] script called from qemu hook freezes.
>
> On Fri, Jan 04, 2019 at 17:27:48 +0100, daggs wrote:
> > Greetings Peter,
> >
> > > Sent: Friday, January 04, 2019 at 4:47 PM
> > > From: "Peter Krempa" <pkre...@redhat.com>
> > > To: daggs <da...@gmx.com>
> > > Cc: libvirt-users@redhat.com
> > > Subject: Re: [libvirt-users] script called from qemu hook freezes.
> > >
> > > On Thu, Jan 03, 2019 at 18:07:58 +0100, daggs wrote:
> > > > Greetings,
> > > >
> > > > I'm executing an external script when the qemu hook is called with
> > > > start or release, the script is rather simple, upon start it iterates
> > > > over the output of lsusb -t and for each device, it looks if it should
> > > > be added to the vm we started, if so, it attaches it to the vm as
> > > > follows:
> > > > virsh --connect qemu:///system "${cmd}" "${domain}" /dev/stdin << END
> > > > <hostdev mode='subsystem' type='usb'>
> > > > <source>
> > > > <address bus='${busnum}' device='${devnum}' />
> > > > </source>
> > > > </hostdev>
> > > > END
> > > >
> > > > where cmd is attach-device, domain is the vm's name, busnum and devnum
> > > > come from the output of the lsusb -t.
> > > > my issue is that upon the first attach attempt, the cmd hangs, I need
> > > > to kill it and after than I cannot preform any virsh cmd, I must
> > > > restart the host.
> > > > if I try to execute the same cmd after the vm is up, it works great.
> > > >
> > > > why the attach process gets stuck? do I need to execute it under
> > > > different stage?
> > >
> > > Hook scripts shall never call any libvirt API (even through virsh). At
> > > the point when the hook script is called the VM startup process is
> > > paused until the script returns. If the script attempts to modify the VM
> > > it gets stuck as the VM is locked at that point.
> > >
> > > You either need to add the device prior to startup, but AFAIK that is
> > > not possible with a hook script or after but the script needs to return.
> > >
> > > So you either fork off a process which will wait for the startup to
> > > finish from the hook script or write an APP using the libvirt API which
> > > will wait for the VM start event and then execute what's necessary.
> > >
> >
> > I see, is there another way to do what I need (on startup usb hotplug) or
> > maybe optional hotplug (e.g. don't fail the device isn't present)?
>
> If you need programatic logic to decide which device to plug in you
> either use the above suggestion to use a daemon using libvirt API or
> fork off a separate process or do the logic prior to start by
> pre-constructing the XML and using 'virsh create xmlfile' which will be
> used as the running config without modifying the persistent one.
>
Laine's suggestion was the missing part, now it is a udev issue as it seems
that not all the usb dev have settled when the rule is executed.
Dagg.
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