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authorreinelt <>2000-04-07 05:42:20 +0000
committerreinelt <>2000-04-07 05:42:20 +0000
commit65540b205445edffe8ca75e7d797ea2f3d9ab41d (patch)
treee289981edc6218ca381876155d0a81cfe527d25e /lock.c
parentccb26ef39584226382cf4b5f895f4e2472975694 (diff)
downloadlcd4linux-65540b205445edffe8ca75e7d797ea2f3d9ab41d.tar.gz
[lcd4linux @ 2000-04-07 05:42:20 by reinelt]
UUCP style lockfiles for the serial port
Diffstat (limited to 'lock.c')
-rw-r--r--lock.c159
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;
+}