From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Xu Subject: Re: [PATCH 3/8] migration: support todetectcompression and decompression errors Date: Wed, 28 Mar 2018 12:20:03 +0800 Message-ID: <20180328042003.GB29554@xz-mi> References: <20180328030351.GU17789@xz-mi> <201803281208196040484@zte.com.cn> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Cc: kvm@vger.kernel.org, mst@redhat.com, mtosatti@redhat.com, xiaoguangrong@tencent.com, qemu-devel@nongnu.org, guangrong.xiao@gmail.com, pbonzini@redhat.com To: jiang.biao2@zte.com.cn Return-path: Content-Disposition: inline In-Reply-To: <201803281208196040484@zte.com.cn> 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 On Wed, Mar 28, 2018 at 12:08:19PM +0800, jiang.biao2@zte.com.cn wrote: > >=20 > > On Tue, Mar 27, 2018 at 10:35:29PM +0800, Xiao Guangrong wrote: > > > >> > > No, we can't make the assumption that "error _must_ be caused by= page update". > >> > > No document/ABI about compress/decompress promised it. :) > > > > Indeed, I found no good documents about below errors that jiang.biao > > pointed out. > Hi, Peter > The description about the errors comes from here, > http://www.zlib.net/manual.html > And about the error codes returned by inflate(), they are described as=EF= =BC=8C > ** inflate() returns=20 > Z_OK if some progress has been made (more input processed or more outpu= t produced), > Z_STREAM_END if the end of the compressed data has been reached and all= uncompressed output has been produced,=20 > Z_NEED_DICT if a preset dictionary is needed at this point,=20 > Z_DATA_ERROR if the input data was corrupted (input stream not conformi= ng to the zlib format or incorrect check value, in which case strm->msg p= oints to a string with a more specific error),=20 > Z_STREAM_ERROR if the stream structure was inconsistent (for example ne= xt_in or next_out was Z_NULL, or the state was inadvertently written over= by the application),=20 > Z_MEM_ERROR if there was not enough memory,=20 > Z_BUF_ERROR if no progress was possible or if there was not enough room= in the output buffer when Z_FINISH is used. ...=20 > ** Ah yes. My bad to be so uncareful. :) > According to the above description, the error caused by page update loo= ks=20 > more like tend to return Z_DATA_ERROR, but I do not have env to verify = that. :) > As I understand it, the real compress/decompress error cases other than= that=20 > caused by page update should be rare, maybe the error code is enough to > distinguish those if we can verify the the error codes returned by page= update > and other silent failures by test. If so, we can cut the cost of memcpy= . =20 > If not, I agree with Guangrong's idea too. I never read the zlib code a= nd all my > information comes from the manual, so if anything inaccurate, pls ignor= e my > option. :) So I suppose all of us know that alternative now, we just need a solid way to confirm the uncertainty. I'll leave this to Guangrong. Thanks, --=20 Peter Xu