[lcd4linux @ 2000-04-07 05:42:20 by reinelt]

UUCP style lockfiles for the serial port

1 files changed, 159 insertions, 0 deletions

diff --git a/lock.c b/lock.c
new file mode 100644
index 0000000..dc83a10
--- /dev/null
+++ b/lock.c
@@ -0,0 +1,159 @@
+/* $Id: lock.c,v 1.1 2000/04/07 05:42:20 reinelt Exp $
+ *
+ * UUCP style locking
+ *
+ * Copyright 1999, 2000 by Michael Reinelt (reinelt@eunet.at)
+ *
+ * This program 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 2, or (at your option)
+ * any later version.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ *
+ * $Log: lock.c,v $
+ * Revision 1.1  2000/04/07 05:42:20  reinelt
+ *
+ * UUCP style lockfiles for the serial port
+ *
+ */
+
+/* 
+ * exported functions:
+ * 
+ * pid_t lock_port (char *port)
+ *   returns 0 if port could be successfully locked
+ *   otherwise returns PID of the process holding the lock
+ *
+ * pid_t unlock_port (char *port)
+ *   returns 0 if port could be successfully unlocked
+ *   otherwise returns PID of the process holding the lock
+ *
+ */
+
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+
+#include "lock.h"
+
+
+pid_t lock_port (char *port)
+{
+  char lockfile[256];
+  char tempfile[256];
+  char buffer[16];
+  char *p;
+  int fd, len, pid;
+
+  if ((p=strrchr (port, '/'))==NULL) 
+    p=port;
+  else
+    p++;
+  
+  snprintf(lockfile, sizeof(lockfile), LOCK, p);
+  snprintf(tempfile, sizeof(tempfile), LOCK, "TMP.XXXXXX");
+
+  if (mktemp(tempfile)==NULL) {
+    fprintf(stderr, "mktemp(%s) failed.\n", tempfile);
+    return -1;
+  }
+  
+  if ((fd=creat(tempfile, 0664))==-1) {
+    fprintf(stderr, "creat(%s) failed: %s\n", tempfile, strerror(errno));
+    return -1;
+  }
+  
+  snprintf (buffer, sizeof(buffer), "%10d\n", (int)getpid());
+  if (write(fd, buffer, strlen(buffer))!=strlen(buffer)) {
+    fprintf(stderr, "write(%s) failed: %s\n", tempfile, strerror(errno));
+    close(fd);
+    unlink(tempfile);
+    return -1;
+  }
+  close (fd);
+  
+
+  while (link(tempfile, lockfile)==-1) {
+
+    if (errno!=EEXIST) {
+      fprintf(stderr, "link(%s, %s) failed: %s\n", tempfile, lockfile, strerror(errno));
+      unlink(tempfile);
+      return -1;
+    }
+
+    if ((fd=open(lockfile, O_RDONLY))==-1) {
+      if (errno==ENOENT) continue; // lockfile disappared
+      fprintf (stderr, "open(%s) failed: %s\n", lockfile, strerror(errno));
+      unlink (tempfile);
+      return -1;
+    }
+
+    len=read(fd, buffer, sizeof(buffer)-1);
+    if (len<0) {
+      fprintf (stderr, "read(%s) failed: %s\n", lockfile, strerror(errno));
+      unlink (tempfile);
+      return -1;
+    }
+    
+    buffer[len]='\0';
+    if (sscanf(buffer, "%d", &pid)!=1 || pid==0) {
+      fprintf (stderr, "scan(%s) failed.\n", lockfile);
+      unlink (tempfile);
+      return -1;
+    }
+
+    if (pid==getpid()) {
+      fprintf (stderr, "%s already locked by us. uh-oh...\n", lockfile);
+      unlink(tempfile);
+      return 0;
+    }
+    
+    if ((kill(pid, 0)==-1) && errno==ESRCH) {
+      fprintf (stderr, "removing stale lockfile %s\n", lockfile);
+      if (unlink(lockfile)==-1 && errno!=ENOENT) {
+	fprintf (stderr, "unlink(%s) failed: %s\n", lockfile, strerror(errno));
+	unlink(tempfile);
+	return pid;
+      }
+      continue;
+    }
+    unlink (tempfile);
+    return pid;
+  }
+  
+  unlink (tempfile);
+  return 0;
+}
+
+
+pid_t unlock_port (char *port)
+{
+  char lockfile[256];
+  char *p;
+  
+  if ((p=strrchr (port, '/'))==NULL) 
+    p=port;
+  else
+    p++;
+  
+  snprintf(lockfile, sizeof(lockfile), LOCK, p);
+  unlink (lockfile);
+  return 0;
+}