[Qemu-devel] Providing a mechanism to reopen() file based chardevs

[Tony Breeds]

Hi All,
    Openstcak (Nova) has had an issue for a longish time where a running
instance (qemu via libvirt) which has a file based console can fill the disk of
the hypervisor causing all guests to stall.

I'm looking at ways to fix this.  Clearly it can be done in openstack wothout
changing qemu but it seems to be that a better idea would be to teach qemu to
reopen() these files when it recieves a sighup and/or something in the monitor.

I like the idea of sighup as it allows systems administrators to use logrotate
thereby avoiding baking policy into qemu.

My initial thoughts are that I'd need to add a flag to the chardev (perhaps
allowreopen?) and upon reciept of the reopen request I'd I iterate over the
open chardevs and reopen them if they have this flag set.

The main target of this would be a console log.

So my main question is would that be something that would be considered for
2.3.0?  If so any high level design points I shoudl consider?

 - Is the chardev flag a good/bad idea?
 - Is it okay to change the action taken by sighup?

Yours Tony.

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