fcntl-linux.h: add new definitions and manual updates for open file description locks

Open file description locks have been merged into the Linux kernel for
v3.15.  Add the appropriate command-value definitions and an update to
the manual that describes their usage.

1 files changed, 77 insertions, 0 deletions

diff --git a/manual/examples/ofdlocks.c b/manual/examples/ofdlocks.c
new file mode 100644
index 0000000..85e193c
--- /dev/null
+++ b/manual/examples/ofdlocks.c
@@ -0,0 +1,77 @@
+/* Open File Description Locks Usage Example
+   Copyright (C) 1991-2014 Free Software Foundation, Inc.
+
+   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
+   of the License, 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, see <http://www.gnu.org/licenses/>.
+*/
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <pthread.h>
+
+#define FILENAME	"/tmp/foo"
+#define NUM_THREADS	3
+#define ITERATIONS	5
+
+void *
+thread_start (void *arg)
+{
+  int i, fd, len;
+  long tid = (long) arg;
+  char buf[256];
+  struct flock lck = {
+    .l_whence = SEEK_SET,
+    .l_start = 0,
+    .l_len = 1,
+  };
+
+  fd = open ("/tmp/foo", O_RDWR | O_CREAT, 0666);
+
+  for (i = 0; i < ITERATIONS; i++)
+    {
+      lck.l_type = F_WRLCK;
+      fcntl (fd, F_OFD_SETLKW, &lck);
+
+      len = sprintf (buf, "%d: tid=%ld fd=%d\n", i, tid, fd);
+
+      lseek (fd, 0, SEEK_END);
+      write (fd, buf, len);
+      fsync (fd);
+
+      lck.l_type = F_UNLCK;
+      fcntl (fd, F_OFD_SETLK, &lck);
+
+      /* sleep to ensure lock is yielded to another thread */
+      usleep (1);
+    }
+  pthread_exit (NULL);
+}
+
+int
+main (int argc, char **argv)
+{
+  long i;
+  pthread_t threads[NUM_THREADS];
+
+  truncate (FILENAME, 0);
+
+  for (i = 0; i < NUM_THREADS; i++)
+    pthread_create (&threads[i], NULL, thread_start, (void *) i);
+
+  pthread_exit (NULL);
+  return 0;
+}