Patch zlib-1.2.7-z-block-flush.patch was added because tigervnc server crashed with zlib 1.2.7. It was deducted that zlib's upstream commit f1ebdd6a9c495a5db9a22aa80dd7d54ae7db42e9 triggered this failure. First of all, I don't see how f1ebdd6a9c4 commit can be wrong ... and so partly reverting the patch (by re-ranking Z_BLOCK flush to stronger flush) does not make sense to me. This patch seems to bring a bug in API. Then, we seem to have no reproducer for this issue, and after a lot of trying I'm not able to reproduce this with Fedora's tigervnc against old (without block-flush.patch) zlib. Perhaps this has been fixed in tigervnc at the end? I was also trying to bulid old tigervnc, but it turns out to be a non-trivial task (tiger vnc brings some xserver versoin-specific set of patches, and unfortunately the old tigervnc 1.1.0 doesn't have a patch for quite new xserver 1.17 (which is now in RHEL 7). Because the downstream patch in zlib seems to be wrong, and looks like it is not needed for tigervnc now -- I'll give it a few days (waiting for any response) and then (when no objections) I'll revert the patch. Any help here would be really appreciated.
Ok, I can confirm that drop of this patch is fairly safe, because upstream of tigervnc applied b5822f32ab5043b4e70e55ccbac0f548a2f784fc commit to fix (work-around zlib) issue. Reverting this patch in EPEL7 leads to tigervnc-server failure (similarly on Fedora) with reproducer: server $ vncserver # starts on :2 client $ vncviewer CompressLevel=2 server:2 with the following server log: Xvnc TigerVNC 1.3.1 - built Jan 29 2017 15:56:11 Copyright (C) 1999-2011 TigerVNC Team and many others (see README.txt) See http://www.tigervnc.org for information on TigerVNC. Underlying X server release 11702000, The X.Org Foundation Mon Jan 30 09:29:43 2017 vncext: VNC extension running! vncext: Listening for VNC connections on all interface(s), port 5903 vncext: created VNC server for screen 0 Mon Jan 30 09:30:00 2017 Connections: accepted: 10.34.4.132::47716 SConnection: Client needs protocol version 3.8 SConnection: Client requests security type VeNCrypt(19) Mon Jan 30 09:30:02 2017 VNCSConnST: Server default pixel format depth 24 (32bpp) little-endian rgb888 VNCSConnST: Client pixel format depth 24 (32bpp) little-endian rgb888 Connections: closed: 10.34.4.132::47716 (ZlibOutStream: deflateParams failed) SMsgWriter: framebuffer updates 1 ...
Fixed in Rawdhide (F26) by: http://pkgs.fedoraproject.org/cgit/rpms/zlib.git/commit/?id=4871b1554bef470feb