From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35315) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fnPBL-0000sv-5J for qemu-devel@nongnu.org; Wed, 08 Aug 2018 10:11:24 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fnPBH-0006JR-5E for qemu-devel@nongnu.org; Wed, 08 Aug 2018 10:11:23 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:47758 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 1fnPBG-0006IX-Vq for qemu-devel@nongnu.org; Wed, 08 Aug 2018 10:11:19 -0400 Date: Wed, 8 Aug 2018 15:11:13 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20180808141112.GK2734@work-vm> References: <20180807091209.13531-1-xiaoguangrong@tencent.com> <20180807091209.13531-9-xiaoguangrong@tencent.com> <20180808050846.GG24415@xz-mi> <503d7733-e2e7-09c5-75a3-1e250f549065@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <503d7733-e2e7-09c5-75a3-1e250f549065@gmail.com> Subject: Re: [Qemu-devel] [PATCH v3 08/10] migration: handle the error condition properly List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Xiao Guangrong Cc: Peter Xu , pbonzini@redhat.com, mst@redhat.com, mtosatti@redhat.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, wei.w.wang@intel.com, jiang.biao2@zte.com.cn, eblake@redhat.com, Xiao Guangrong * Xiao Guangrong (guangrong.xiao@gmail.com) wrote: > > > On 08/08/2018 01:08 PM, Peter Xu wrote: > > On Tue, Aug 07, 2018 at 05:12:07PM +0800, guangrong.xiao@gmail.com wrote: > > > From: Xiao Guangrong > > > > > > ram_find_and_save_block() can return negative if any error hanppens, > > > however, it is completely ignored in current code > > > > Could you hint me where we'll return an error? > > > > I think control_save_page() may return a error condition but i am not > good at it ... Other places look safe _currently_. These functions were > designed to have error returned anyway. ram_control_save_page's return is checked by control_save_page which returns true/false but sets *pages to a return value. What I'd need to follow closely is the case where ram_control_save_page returns RAM_SAVE_CONTROL_DELAYED, in that case control_save_page I think returns with *pages=-1 and returns true. And I think in that case ram_save_target_page can leak that -1 - hmm. Now, ram_save_host_page already checks for <0 and will return that, but I think that would potentially loop in ram_find_and_save_block; I'm not sure we want to change that or not! Dave > > > (Anyway I agree that the error handling is not that good, mostly > > because the QEMUFile APIs does not provide proper return code, e.g., > > qemu_put_be64 returns void) > > > > Yes, it is, the returned error condition is mixed in file's API and > function's return value... :( > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK