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Diffstat (limited to '')
| -rw-r--r-- | lock.c | 159 |
1 files changed, 159 insertions, 0 deletions
@@ -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; +} |