VNC reverse broken in qemu 2.6.0

[Andreas Hofmeister]

Hi all,

I recently tried to upgrade from Qemu 2.4.1 to 2.6.0, but found some problems with VNC reverse connections.

1) In "-vnc 172.16.1.3:5902,reverse" used to mean "connect to port 5902"
   That seems to have changed changed since 2.4.1, the thing after the IP address is now interpreted
   as a display number. If that change was intentional, the man-page needs to be fixed.

2) After subtracting 5900 from that port number (-vnc 172.16.1.3:2,reverse), I ran into a segfault.

---8<---
Program received signal SIGSEGV, Segmentation fault.
qio_channel_socket_get_local_address (ioc=0x0, errp=errp@entry=0x7fffffffe118) at io/channel-socket.c:33
33 return socket_sockaddr_to_address(&ioc->localAddr,
(gdb) bt
#0 qio_channel_socket_get_local_address (ioc=0x0, errp=errp@entry=0x7fffffffe118) at io/channel-socket.c:33
#1 0x000055555594c0f5 in vnc_init_basic_info_from_server_addr (errp=0x7fffffffe118, info=0x555558f35990,
    ioc=<optimized out>) at ui/vnc.c:146
#2 vnc_server_info_get (vd=0x7fffecc4b010) at ui/vnc.c:223
#3 0x000055555595192a in vnc_qmp_event (vs=0x555558f41f30, vs=0x555558f41f30, event=QAPI_EVENT_VNC_CONNECTED)
    at ui/vnc.c:279
#4 vnc_connect (vd=vd@entry=0x7fffecc4b010, sioc=sioc@entry=0x555558f34c00, skipauth=skipauth@entry=false,
    websocket=websocket@entry=false) at ui/vnc.c:2994
#5 0x00005555559520d8 in vnc_display_open (id=id@entry=0x555556437650 "default", errp=errp@entry=0x7fffffffe228)
    at ui/vnc.c:3773
#6 0x0000555555952fd3 in vnc_init_func (opaque=<optimized out>, opts=<optimized out>, errp=<optimized out>)
    at ui/vnc.c:3868
#7 0x0000555555a011da in qemu_opts_foreach (list=<optimized out>, func=0x555555952fa0 <vnc_init_func>, opaque=0x0,
    errp=0x0) at util/qemu-option.c:1116
#8 0x00005555556dcfbe in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4592
--->8---

A git bisect shows that this happens since

---8<---
commit 98481bfcd661daa3c160cc87a297b0e60a307788
Author: Eric Blake <email address hidden>
Date: Mon Oct 26 16:34:45 2015 -0600

    vnc: Hoist allocation of VncBasicInfo to callers
--->8---

TIA
  Andi

[Thomas Huth (th-huth)]

I think this has been fixed in QEMU 2.7, likely with the following commit:
http://git.qemu.org/?p=qemu.git;a=commitdiff;h=3e7f136d8b4383d99f