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From: Branden Robinson <branden@debian.org>
Date: Wed, 20 Aug 2008 02:56:41 +0200
Subject: add support for logfile rotation
- Implement new ReopenLogFile() and ReopenLogFileNotify() functions.
ReopenLogFileNotify() is a signal handler for SIGUSR2.
- Move the definition of the WRITES() macro from error.c to dm_error.h
so that dm.c can use it as well.
- Document xdm's signal handling in its manpage.
Forward-ported by Eugene Konev and Julien Cristau.
Last-Updated: 2025-12-08
---
include/dm_error.h | 2 ++
man/xdm.man | 31 +++++++++++++++++++++++++++++++
xdm/dm.c | 40 +++++++++++++++++++++++++++++++++++++++-
3 files changed, 72 insertions(+), 1 deletion(-)
diff --git a/xdm/dm.c b/xdm/dm.c
index 73280b2..864c5aa 100644
--- a/xdm/dm.c
+++ b/xdm/dm.c
@@ -83,8 +83,10 @@ from The Open Group.
# endif
#endif
-static void StopAll (int n), RescanNotify (int n);
+static void StopAll (int n), RescanNotify (int n),
+ ReopenLogFileNotify (int n);
static void RescanServers (void);
+static void ReopenLogFile (void);
static void RestartDisplay (struct display *d, int forceReserver);
static void ScanServers (void);
static void SetAccessFileTime (void);
@@ -93,6 +95,7 @@ static void StartDisplays (void);
static void TerminateProcess (pid_t pid, int signal);
volatile int Rescan;
+volatile int Reopen;
static long ServersModTime, ConfigModTime, AccessFileModTime;
int nofork_session = 0;
@@ -242,6 +245,7 @@ main (int argc, char **argv)
AddOtherEntropy();
#endif
(void) Signal (SIGHUP, RescanNotify);
+ (void) Signal (SIGUSR2, ReopenLogFileNotify);
(void) Signal (SIGCHLD, ChildNotify);
Debug ("startup successful; entering main loop\n");
while (
@@ -250,6 +254,11 @@ main (int argc, char **argv)
#endif
AnyDisplaysLeft ())
{
+ if (Reopen)
+ {
+ ReopenLogFile ();
+ Reopen = 0;
+ }
if (Rescan)
{
RescanServers ();
@@ -274,10 +283,31 @@ RescanNotify (int n)
int olderrno = errno;
Debug ("Caught SIGHUP\n");
+ Reopen = 1;
Rescan = 1;
errno = olderrno;
}
+/*
+ * Handle a SIGUSR2: set variable that will instruct the main loop to
+ * reopen the log file.
+ */
+static void
+ReopenLogFileNotify (int n)
+{
+#ifdef SIGNALS_RESET_WHEN_CAUGHT
+ int olderrno = errno;
+#endif
+
+ /* Debug() is not safe inside a signal handler. */
+ WRITES(STDERR_FILENO, "ReopenLogFileNotify handling SIGUSR2\n");
+ Reopen = 1;
+#ifdef SIGNALS_RESET_WHEN_CAUGHT
+ (void) Signal (SIGUSR2, ReopenLogFileNotify);
+ errno = olderrno;
+#endif
+}
+
static void
ScanServers (void)
{
@@ -345,6 +375,14 @@ RescanServers (void)
StartDisplays ();
}
+static void
+ReopenLogFile (void)
+{
+ Debug ("closing standard error file descriptor %d\n", STDERR_FILENO);
+ close (STDERR_FILENO);
+ InitErrorLog ();
+}
+
static void
SetConfigFileTime (void)
{
diff --git a/include/dm_error.h b/include/dm_error.h
index 09c124e..da94cc7 100644
--- a/include/dm_error.h
+++ b/include/dm_error.h
@@ -34,6 +34,8 @@ authorization.
#ifndef _DM_ERROR_H_
# define _DM_ERROR_H_ 1
+#define WRITES(fd, buf) write(fd, buf, strlen(buf))
+
extern void Debug (const char * fmt, ...) _X_ATTRIBUTE_PRINTF(1,2);
extern void InitErrorLog (void);
extern void LogAppend (const char * fmt, ...) _X_ATTRIBUTE_PRINTF(1,2);
diff --git a/man/xdm.man b/man/xdm.man
index 5e63e48..734942a 100644
--- a/man/xdm.man
+++ b/man/xdm.man
@@ -1420,6 +1420,37 @@ isn't very good at doing is coexisting with other window systems. To use
multiple window systems on the same hardware, you'll probably be more
interested in
.I xinit.
+.SH "ASYNCHRONOUS EVENTS"
+.B xdm
+uses
+.B SIGALRM
+and
+.B SIGUSR1
+for its own inter-process communication purposes, managing the relationship
+between the parent
+.B xdm
+process and its children.
+Sending these signals to any
+.B xdm
+process may result in unexpected behavior.
+.TP
+.B SIGHUP
+causes
+.B xdm
+to rescan its configuration files and reopen its log file.
+.TP
+.B SIGTERM
+causes
+.B xdm
+to terminate its children and shut down.
+.TP
+.B SIGUSR2
+causes
+.B xdm
+to reopen its log file.
+This is useful if log rotation is desired, but
+.B SIGHUP
+is too disruptive.
.SH FILES
.TP 20
.I XDMDIR/xdm-config
|
