From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41862) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1duIUq-00077v-7T for qemu-devel@nongnu.org; Tue, 19 Sep 2017 09:23:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1duIUk-0001bb-Jl for qemu-devel@nongnu.org; Tue, 19 Sep 2017 09:23:28 -0400 References: <20170919102434.21147-1-pbonzini@redhat.com> <20170919102434.21147-5-pbonzini@redhat.com> <20170919125300.GL9536@redhat.com> <20170919131208.GM9536@redhat.com> From: Paolo Bonzini Message-ID: Date: Tue, 19 Sep 2017 15:23:09 +0200 MIME-Version: 1.0 In-Reply-To: <20170919131208.GM9536@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 4/4] scsi: add persistent reservation manager using qemu-pr-helper List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org 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 =3D 0; attempts < PR_MAX_RECONNECT_ATTEMPTS; atte= mpts++) { >>> >>> I'm curious why you need to loop here. The helper daemon should be ru= nning >>> already, as you're not spawning it on demand IIUC. So it shoudl eithe= r >>> 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-friendl= y, >> but it is nicer for testing and it is also the only possibility for us= er >> 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. >=20 > If using systemd socket activation and you restart the daemon, the list= ening > socket should be preserved, so you shouldn't need to reconnect - the cl= ient > 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