(lock_db): New function.

(unlock_db): New function.

src/server/lockdb.c

+/*
+ * Lock and unlock the database.
+ * Copyright (C) 1999  Lysator Academic Computer Association.
+ *
+ * This file is part of the LysKOM server.
+ * 
+ * LysKOM is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by 
+ * the Free Software Foundation; either version 1, or (at your option) 
+ * any later version.
+ * 
+ * LysKOM is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with LysKOM; see the file COPYING.  If not, write to
+ * Lysator, c/o ISY, Linkoping University, S-581 83 Linkoping, SWEDEN,
+ * or the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, 
+ * MA 02139, USA.
+ *
+ * Please mail bug reports to bug-lyskom@lysator.liu.se. 
+ */
+
+#include <config.h>
+
+#include <sys/param.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#ifdef HAVE_STRING_H
+#  include <string.h>
+#else
+#  ifdef HAVE_STRINGS_H
+#    include <strings.h>
+#  endif
+#endif
+#ifndef HAVE_STRCHR
+#  define strchr index
+#endif
+#include <stdlib.h>
+#include <signal.h>
+
+#include "lockdb.h"
+#include "log.h"
+#include "kom-types.h"
+#include "param.h"
+#include "lyskomd.h"
+
+int lock_db(void)
+{
+    char new_lock[MAXHOSTNAMELEN + 3 + 3 * sizeof(pid_t)];
+    char current_lock[MAXHOSTNAMELEN + 4 + 3 * sizeof(pid_t)];
+    char *end;
+    int retry;
+    size_t sz;
+    size_t ix;
+    pid_t pid;
+    
+
+    if (gethostname(new_lock, MAXHOSTNAMELEN) == -1)
+	restart_kom("gethostname failed (%d)\n", errno);
+
+    new_lock[MAXHOSTNAMELEN+1] = '\0';
+    end = strchr(new_lock, '\0');
+    sprintf(end, ":%ld", (long)getpid());
+
+    for (retry = 0; retry < 2; ++retry)
+    {
+	if (symlink(new_lock, param.lockfile_name) == 0)
+	{
+	    kom_log("Created lock %s\n", param.lockfile_name);
+	    return 0;
+	}
+	
+	if (errno != EEXIST)
+	    restart_kom("Failed to create lock symlink %s "
+			"pointing to %s: %d\n", param.lockfile_name,
+			new_lock, errno);
+
+	if (retry)
+	{
+	    kom_log("Lock file recreated by some other party\n");
+	    return -1;
+	}
+
+	sz = readlink(param.lockfile_name, current_lock, sizeof(current_lock));
+	if (sz >= sizeof(current_lock) - 1)
+	    restart_kom("Too much data in lock symlink %s\n",
+			param.lockfile_name);
+	current_lock[sz] = '\0';
+
+	for (ix = 0; ix < sizeof(new_lock); ++ix)
+	{
+	    if (new_lock[ix] != current_lock[ix])
+	    {
+		kom_log("Database locked by %s\n", current_lock);
+		return -1;
+	    }
+
+	    if (new_lock[ix] == ':')
+		break;
+	}
+
+	pid = strtol(&current_lock[ix+1], &end, 10);
+	if (end == &current_lock[ix+1])
+	    restart_kom("Broken lock symlink %s: %s\n",
+			param.lockfile_name, current_lock);
+
+	if (kill(pid, 0) == 0 || errno != ESRCH)
+	{
+	    kom_log("Database locked by %s\n", current_lock);
+	    return -1;
+	}
+
+	/* The process is dead.  Remove the stale lock file.  If it
+	   was just removed by a dying process -- fine.  */
+	if (remove(param.lockfile_name) < 0 && errno != ENOENT)
+	    restart_kom("Failed to remove stale lock symlink %s\n",
+			param.lockfile_name);
+    }
+    restart_kom("Unreachable code reached in lock_db.\n");
+}
+
+void
+unlock_db(void)
+{
+    if (remove(param.lockfile_name) < 0)
+	restart_kom("Failed to remove lock file %s\n", param.lockfile_name);
+}

src/server/lockdb.h

+/*
+ * Lock and unlock the database.
+ * Copyright (C) 1999  Lysator Academic Computer Association.
+ *
+ * This file is part of the LysKOM server.
+ * 
+ * LysKOM is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by 
+ * the Free Software Foundation; either version 1, or (at your option) 
+ * any later version.
+ * 
+ * LysKOM is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with LysKOM; see the file COPYING.  If not, write to
+ * Lysator, c/o ISY, Linkoping University, S-581 83 Linkoping, SWEDEN,
+ * or the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, 
+ * MA 02139, USA.
+ *
+ * Please mail bug reports to bug-lyskom@lysator.liu.se. 
+ */
+
+/* Attempt to lock the database.  Returns 0 on success, or -1 if the
+   database is already locked.  If it is locked, an error message will
+   be written using kom_log().  */
+int lock_db(void);
+
+/* Unlock the database. */
+void unlock_db(void);