From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50787) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1duI5Y-0001nS-61 for qemu-devel@nongnu.org; Tue, 19 Sep 2017 08:57:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1duI5T-0007vy-8q for qemu-devel@nongnu.org; Tue, 19 Sep 2017 08:57:20 -0400 References: <20170919102434.21147-1-pbonzini@redhat.com> <20170919102434.21147-5-pbonzini@redhat.com> <20170919125300.GL9536@redhat.com> From: Paolo Bonzini Message-ID: Date: Tue, 19 Sep 2017 14:57:00 +0200 MIME-Version: 1.0 In-Reply-To: <20170919125300.GL9536@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 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. Paolo