From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dr. David Alan Gilbert" Subject: Re: [PATCH v3 08/10] migration: handle the error condition properly Date: Wed, 8 Aug 2018 15:11:13 +0100 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 Cc: kvm@vger.kernel.org, mst@redhat.com, mtosatti@redhat.com, Xiao Guangrong , qemu-devel@nongnu.org, Peter Xu , wei.w.wang@intel.com, jiang.biao2@zte.com.cn, pbonzini@redhat.com To: Xiao Guangrong Return-path: Content-Disposition: inline In-Reply-To: <503d7733-e2e7-09c5-75a3-1e250f549065@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org * 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