On Tue, Mar 27, 2018 at 10:35:29PM +0800, Xiao Guangrong wrote: > > > On 03/28/2018 08:43 AM, jiang.biao2@xxxxxxxxxx wrote: > > > On 03/27/2018 07:17 PM, Peter Xu wrote: > > > > On Tue, Mar 27, 2018 at 03:42:32AM +0800, Xiao Guangrong wrote: > > > > > > > > [...] > > > > > > > > > > It'll be understandable to me if the problem is that the compress() > > > > > > API does not allow the input buffer to be changed during the whole > > > > > > period of the call. If that is a must, this patch for sure helps. > > > > > > > > > > Yes, that is exactly what i want to say. :) > > > > > > > > So I think now I know what this patch is for. :) And yeah, it makes > > > > sense. > > > > > > > > Though another question would be: if the buffer is updated during > > > > compress() and compress() returned error, would that pollute the whole > > > > z_stream or it only fails the compress() call? > > > > > > > > > > I guess deflateReset() can recover everything, i.e, keep z_stream as > > > it is init'ed by deflate_init(). > > > > > > > (Same question applies to decompress().) > > > > > > > > If it's only a compress() error and it won't pollute z_stream (or say, > > > > it can be recovered after a deflateReset() and then we can continue to > > > > call deflate() without problem), then we'll actually have two > > > > alternatives to solve this "buffer update" issue: > > > > > > > > 1. Use the approach of current patch: we copy the page every time, so > > > > deflate() never fails because update never happens. But it's slow > > > > since we copy the pages every time. > > > > > > > > 2. Use the old approach, and when compress() fail, we just ignore that > > > > page (since now we know that error _must_ be caused by page update, > > > > then we are 100% sure that we'll send that page again so it'll be > > > > perfectly fine). > > > > > > > > > > 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. > > So, as I metioned before, can we just distingush the decompress/compress errors > > from errors caused by page update by the return code of inflate/deflate? > > According to the zlib manual, there seems to be several error codes for different > > cases, > > #define Z_ERRNO (-1) > > #define Z_STREAM_ERROR (-2) > > #define Z_DATA_ERROR (-3) > > #define Z_MEM_ERROR (-4) > > #define Z_BUF_ERROR (-5) > > #define Z_VERSION_ERROR (-6) > > Did you check the return code when silent failure(not caused by page update) > > happened before? :) > > I am afraid there is no such error code and i guess zlib is not designed to > compress the data which is being modified. So I agree with you, maybe the only right way to do now is copy the page, until we know better about zlib and find something useful. Thanks! -- Peter Xu
