From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH 3/8] migration: support todetectcompression and decompression errors Date: Wed, 28 Mar 2018 02:44:21 +0800 Message-ID: References: <20180328030351.GU17789@xz-mi> <201803281208196040484@zte.com.cn> <20180328042003.GB29554@xz-mi> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: kvm@vger.kernel.org, mst@redhat.com, mtosatti@redhat.com, xiaoguangrong@tencent.com, qemu-devel@nongnu.org, pbonzini@redhat.com To: Peter Xu , jiang.biao2@zte.com.cn Return-path: In-Reply-To: <20180328042003.GB29554@xz-mi> Content-Language: en-US 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 03/28/2018 12:20 PM, Peter Xu wrote: > On Wed, Mar 28, 2018 at 12:08:19PM +0800, jiang.biao2@zte.com.cn wrote: >>> >>> 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， >> ** inflate() returns >> Z_OK if some progress has been made (more input processed or more output produced), >> Z_STREAM_END if the end of the compressed data has been reached and all uncompressed output has been produced, >> Z_NEED_DICT if a preset dictionary is needed at this point, >> Z_DATA_ERROR if the input data was corrupted (input stream not conforming to the zlib format or incorrect check value, in which case strm->msg points to a string with a more specific error), >> Z_STREAM_ERROR if the stream structure was inconsistent (for example next_in or next_out was Z_NULL, or the state was inadvertently written over by the application), >> Z_MEM_ERROR if there was not enough memory, >> Z_BUF_ERROR if no progress was possible or if there was not enough room in the output buffer when Z_FINISH is used. ... >> ** > > Ah yes. My bad to be so uncareful. :) > >> According to the above description, the error caused by page update looks >> more like tend to return Z_DATA_ERROR, but I do not have env to verify that. :) No, still lack info to confirm the case of compressing the data being updated is the only one to return Z_DATA_ERROR. And nothing provided that no other error condition causes data corrupted will be squeezed into this error code. >> As I understand it, the real compress/decompress error cases other than that >> 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. Please note, compare with other operations, e.g, compression, detect zero page, etc., memcpy() is not a hot function at all. >> If not, I agree with Guangrong's idea too. I never read the zlib code and all my >> information comes from the manual, so if anything inaccurate, pls ignore 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. Yes, i still prefer to memcpy() to make it safe enough to protect our production unless we get enough certainty to figure out the error conditions. Thanks!