On 19/09/2017 15:12, Daniel P. Berrange wrote: > On Tue, Sep 19, 2017 at 02:57:00PM +0200, Paolo Bonzini wrote: >> On 19/09/2017 14:53, Daniel P. Berrange wrote: >>>> + /* Try to reconnect while sending the CDB. */ >>>> + for (attempts = 0; attempts < PR_MAX_RECONNECT_ATTEMPTS; attempts++) { >>> >>> I'm curious why you need to loop here. The helper daemon should be running >>> already, as you're not spawning it on demand IIUC. So it shoudl either >>> succeed first time, or fail every time. >> >> You're focusing on the usecase where the helper daemon is spawned per-VM >> by the system libvirtd, which I agree is the most important one. >> However, the other usecase is the one with a global daemon, access to >> which is controlled via Unix permissions. This is not SELinux-friendly, >> but it is nicer for testing and it is also the only possibility for user >> libvirtd. >> >> In that case, upgrading QEMU on the host could result in a "systemctl >> restart qemu-pr-helper.service" (or, hopefully unlikely, a crash could >> result in systemd respawning the daemon). Reconnect is useful in that case. > > If using systemd socket activation and you restart the daemon, the listening > socket should be preserved, so you shouldn't need to reconnect - the client > should get queued until it has started again (likewise on crash).
Oh, that's cool. I didn't know that. However, systemd socket activation is optional, and it's only a handful of lines so I think it's a bit nicer behavior (chardevs for example have options to reconnect). Paolo