with-lock-ex: Replace ad-hoc option parser with getopt.

[chiark-utils.git] / cprogs / with-lock-ex.c

diff --git a/cprogs/with-lock-ex.c b/cprogs/with-lock-ex.c
index 1850d1f0283bd61fc1da12458cba7ec0a227c572..d1b23db9064a32bd520783e1473dd9393788442d 100644 (file)
--- a/cprogs/with-lock-ex.c
+++ b/cprogs/with-lock-ex.c
@@ -1,12 +1,17 @@
 /*
  * File locker
  *
- * Usage: with-lock-ex -<mode> <lockfile> <command> <args>...
+ * Usage:
+ *  with-lock-ex -<mode> <lockfile> <command> <args>...
+ *  with-lock-ex -l      <lockfile>
  *
  * modes are
  *  w    wait for the lock
  *  f    fail if the lock cannot be acquired
  *  q    silently do nothing if the lock cannot be acquired
+ *  l    show who is waiting (print "none" or "read <pid>"
+ *         or "write <pid>"; lockfile opened for reading;
+ *         no command may be specified)
  *
  * with-lock-ex will open and lock the lockfile for writing and
  * then feed the remainder of its arguments to exec(2); when
@@ -17,7 +22,31 @@
  * compatibility with an earlier version).
  *
  * This file written by me, Ian Jackson, in 1993, 1994, 1995, 1996,
- * 1998, 1999.  I hereby place it in the public domain.
+ * 1998, 1999, 2016.
+ *
+ * Copyright 1993-2016 Ian Jackson in some jurisdictions
+ * Copyright 2017      Ian Jackson in all jurisdictions
+ * Copyright 2017      Genome Research Ltd
+ *
+ * (MIT licence:)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * SOFTWARE IN THE PUBLIC INTEREST, INC. BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
  */
 
 #include <errno.h>
@@ -37,44 +66,80 @@ static void fail(const char *why) {
   exit(255);
 }
 
+static void badusage(void) __attribute__((noreturn));
+
+static void badusage(void) {
+    fputs("usage: with-lock-ex -w|-q|-f [-t <secs>] <lockfile> <command> <args>...\n"
+         "       with-lock-ex -l       <lockfile>\n"
+         "       with-lock-ex          <lockfile> <command> <args>...\n",
+         stderr);
+    exit(255);
+}
+
+static int mode;
+
 int main(int argc, char **argv) {
-  int fd, mode, um;
+  int fd, um, c;
   struct stat stab, fstab;
   long cloexec;
   struct flock fl;
-  const char *p;
-
-  if (argc >= 3 && !strcmp((p= strrchr(argv[0],'/')) ? ++p : argv[0], "with-lock")) {
-    mode= 'f';
-  } else if (argc < 4 || argv[1][0] != '-' || argv[1][2] ||
-            ((mode= argv[1][1]) != 'w' && mode != 'q' && mode != 'f')) {
-    fputs("usage: with-lock-ex -w|-q|-f <lockfile> <command> <args>...\n"
-         "       with-lock             <lockfile> <command> <args>...\n",
-         stderr);
-    exit(255);
-  } else {
-    argv++; argc--;
+
+  mode= 'x';
+  while ((c= getopt(argc,argv,"+wfqlt:")) != -1) {
+    switch(c) {
+    case 'l':
+    case 'w':
+    case 'f':
+    case 'q':
+      if (mode != 'x') badusage();
+      mode= c;
+      break;
+    default:
+      badusage();
+    }
   }
+
+  argv += optind-1; argc -= optind-1;
+  if (argc < 2) badusage();
+
   cmd= argv[2];
   um= umask(0777); if (um==-1) fail("find umask");
   if (umask(um)==-1) fail("reset umask");
 
   for (;;) {
-  
-    fd= open(argv[1],O_RDWR|O_CREAT,0666&~(um|((um&0222)<<1)));
+
+    int openmode = mode=='l' ? O_RDONLY : O_RDWR|O_CREAT;
+
+    fd= open(argv[1],openmode,0666&~(um|((um&0222)<<1)));
     if (fd<0) fail(argv[1]);
   
     for (;;) {
       fl.l_type= F_WRLCK;
       fl.l_whence= SEEK_SET;
       fl.l_start= 0;
-      fl.l_len= 1;
-      if (fcntl(fd, mode=='w' ? F_SETLKW : F_SETLK, &fl) != -1) break;
+      fl.l_len= mode=='l' ? 0 : 1;
+      if (fcntl(fd,
+               mode=='l' ? F_GETLK :
+               mode=='w' ? F_SETLKW :
+               F_SETLK,
+               &fl) != -1) break;
       if (mode=='q' &&
          (errno == EAGAIN || errno == EWOULDBLOCK || errno == EBUSY))
        exit(0);
       if (errno != EINTR) fail("could not acquire lock");
     }
+    if (mode=='l') {
+      if (fl.l_pid) {
+       printf("%s %lu\n",
+              fl.l_type == F_WRLCK ? "write" :
+              fl.l_type == F_RDLCK ? "read" : "unknown",
+              (unsigned long)fl.l_pid);
+      } else {
+       printf("none\n");
+      }
+      if (ferror(stdout)) fail("print to stdout\n");
+      exit(0);
+    }
 
     if (fstat(fd, &fstab)) fail("could not fstat lock fd");
     if (stat(argv[1], &stab)) {