[PATCH xserver 06/24] os/xdmcp: Just send XDMCP keepalive packets once every three minutes

[Keith Packard]

There was a complicated scheme to increase the time between keepalives
from 3 minutes up to as much as 24 hours in an attempt to reduce
network traffic from idle X terminals. X terminals receiving X
traffic, or receiving user input would use the 3 minute value; X
terminals without any network traffic would use a longer value.

However, this was actually broken -- any activity in the X server,
either client requests or user input, would end up resetting the
keepalive timeout, so a user mashing on the keyboard would never
discover that the XDMCP master had disappeared and have the session
terminated, which was precisely the design goal of the XDMCP keepalive
mechanism.

Instead of attempting to fix this, accept the cost of a pair of XDMCP
packets once every three minutes and just perform keepalives
regularly.

This will also make reworking the block and wakeup handler APIs to
eliminate select masks easier.

Signed-off-by: Keith Packard <keithp at keithp.com>
---
 os/xdmcp.c | 20 ++------------------
 1 file changed, 2 insertions(+), 18 deletions(-)

diff --git a/os/xdmcp.c b/os/xdmcp.c
index b1ee5d2..7939b41 100644
--- a/os/xdmcp.c
+++ b/os/xdmcp.c
@@ -84,8 +84,6 @@ static int req_socklen;
 static CARD32 SessionID;
 static CARD32 timeOutTime;
 static int timeOutRtx;
-static CARD32 defaultKeepaliveDormancy = XDM_DEF_DORMANCY;
-static CARD32 keepaliveDormancy = XDM_DEF_DORMANCY;
 static CARD16 DisplayNumber;
 static xdmcp_states XDM_INIT_STATE = XDM_OFF;
 
@@ -632,6 +630,7 @@ XdmcpOpenDisplay(int sock)
     if (state != XDM_AWAIT_MANAGE_RESPONSE)
         return;
     state = XDM_RUN_SESSION;
+    timeOutTime = GetTimeInMillis() + XDM_DEF_DORMANCY * 1000;
     sessionSocket = sock;
 }
 
@@ -689,7 +688,6 @@ XdmcpWakeupHandler(void *data,        /* unused */
                    int i, void *pReadmask)
 {
     fd_set *last_select_mask = (fd_set *) pReadmask;
-    fd_set devicesReadable;
 
     if (state == XDM_OFF)
         return;
@@ -704,13 +702,6 @@ XdmcpWakeupHandler(void *data,        /* unused */
             FD_CLR(xdmcpSocket6, last_select_mask);
         }
 #endif
-        XFD_ANDSET(&devicesReadable, last_select_mask, &EnabledDevices);
-        if (XFD_ANYSET(&devicesReadable)) {
-            if (state == XDM_RUN_SESSION)
-                keepaliveDormancy = defaultKeepaliveDormancy;
-        }
-        if (XFD_ANYSET(&AllClients) && state == XDM_RUN_SESSION)
-            timeOutTime = GetTimeInMillis() + keepaliveDormancy * 1000;
     }
     else if (timeOutTime && (int) (GetTimeInMillis() - timeOutTime) >= 0) {
         if (state == XDM_RUN_SESSION) {
@@ -1399,15 +1390,8 @@ recv_alive_msg(unsigned length)
     if (XdmcpReadCARD8(&buffer, &SessionRunning) &&
         XdmcpReadCARD32(&buffer, &AliveSessionID)) {
         if (SessionRunning && AliveSessionID == SessionID) {
-            /* backoff dormancy period */
             state = XDM_RUN_SESSION;
-            if ((GetTimeInMillis() - LastEventTime(XIAllDevices).milliseconds) >
-                keepaliveDormancy * 1000) {
-                keepaliveDormancy <<= 1;
-                if (keepaliveDormancy > XDM_MAX_DORMANCY)
-                    keepaliveDormancy = XDM_MAX_DORMANCY;
-            }
-            timeOutTime = GetTimeInMillis() + keepaliveDormancy * 1000;
+            timeOutTime = GetTimeInMillis() + XDM_DEF_DORMANCY * 1000;
         }
         else {
             XdmcpDeadSession("Alive response indicates session dead");
-- 
2.5.0