From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36757) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fLuqN-0002KN-OJ for qemu-devel@nongnu.org; Thu, 24 May 2018 14:20:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fLuqH-0006bm-TZ for qemu-devel@nongnu.org; Thu, 24 May 2018 14:20:07 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:37250 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fLuqH-0006bb-Oc for qemu-devel@nongnu.org; Thu, 24 May 2018 14:20:01 -0400 Date: Thu, 24 May 2018 21:20:00 +0300 From: "Michael S. Tsirkin" Message-ID: <20180524211726-mutt-send-email-mst@kernel.org> References: <1527176250-178968-1-git-send-email-mst@redhat.com> <70262dde-3b96-b650-f0fb-8143e869c4ab@redhat.com> <20180524190123-mutt-send-email-mst@kernel.org> <6492471e-f8a7-5f5b-9cf9-95cb604f203a@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6492471e-f8a7-5f5b-9cf9-95cb604f203a@redhat.com> Subject: Re: [Qemu-devel] [PATCH v2 2/1] libqtest: add more exit status checks List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: qemu-devel@nongnu.org, Thomas Huth , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Markus Armbruster On Thu, May 24, 2018 at 01:16:24PM -0500, Eric Blake wrote: > On 05/24/2018 11:01 AM, Michael S. Tsirkin wrote: > > On Thu, May 24, 2018 at 11:00:19AM -0500, Eric Blake wrote: > > > On 05/24/2018 10:52 AM, Eric Blake wrote: > > > > > > > Also, since waitpid() can only return either s->qemu_pid or -1 as we > > > > aren't using WNOHANG, it may also be worth asserting that if pid == -1, > > > > we either have EAGAIN (but why aren't we looping in that case?) or > > > > ECHILD. > > > > > > I meant EINTR, not EAGAIN. But in general, using waitpid() to collect > > > process status without doing it in a loop is risky. > > > > Interesting. Risky how? > > If your process has any signal handler installed, then an EINTR failure > means you interpret a transient failure to grab process status (because your > check was interrupted by something else) as a permanent failure, unless you > go back to another waitpid() in a loop. I don't think we have a handler installed, though. > -- > Eric Blake, Principal Software Engineer > Red Hat, Inc. +1-919-301-3266 > Virtualization: qemu.org | libvirt.org