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+/*++
+/* NAME
+/* deliver_flock 3
+/* SUMMARY
+/* lock open file for mail delivery
+/* SYNOPSIS
+/* #include <deliver_flock.h>
+/*
+/* int deliver_flock(fd, lock_style, why)
+/* int fd;
+/* int lock_style;
+/* VSTRING *why;
+/* DESCRIPTION
+/* deliver_flock() sets one exclusive kernel lock on an open file,
+/* for example in order to deliver mail.
+/* It performs several non-blocking attempts to acquire an exclusive
+/* lock before giving up.
+/*
+/* Arguments:
+/* .IP fd
+/* A file descriptor that is associated with an open file.
+/* .IP lock_style
+/* A locking style defined in myflock(3).
+/* .IP why
+/* A null pointer, or storage for diagnostics.
+/* DIAGNOSTICS
+/* deliver_flock() returns -1 in case of problems, 0 in case
+/* of success. The reason for failure is returned via the \fIwhy\fR
+/* parameter.
+/* CONFIGURATION PARAMETERS
+/* deliver_lock_attempts, number of locking attempts
+/* deliver_lock_delay, time in seconds between attempts
+/* sun_mailtool_compatibility, disable kernel locking
+/* LICENSE
+/* .ad
+/* .fi
+/* The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/* Wietse Venema
+/* IBM T.J. Watson Research
+/* P.O. Box 704
+/* Yorktown Heights, NY 10598, USA
+/*--*/
+
+/* System library. */
+
+#include "sys_defs.h"
+#include <unistd.h>
+
+/* Utility library. */
+
+#include <vstring.h>
+#include <myflock.h>
+#include <iostuff.h>
+
+/* Global library. */
+
+#include "mail_params.h"
+#include "deliver_flock.h"
+
+/* Application-specific. */
+
+#define MILLION 1000000
+
+/* deliver_flock - lock open file for mail delivery */
+
+int deliver_flock(int fd, int lock_style, VSTRING *why)
+{
+ int i;
+
+ for (i = 1; /* void */ ; i++) {
+ if (myflock(fd, lock_style,
+ MYFLOCK_OP_EXCLUSIVE | MYFLOCK_OP_NOWAIT) == 0)
+ return (0);
+ if (i >= var_flock_tries)
+ break;
+ rand_sleep(var_flock_delay * MILLION, var_flock_delay * MILLION / 2);
+ }
+ if (why)
+ vstring_sprintf(why, "unable to lock for exclusive access: %m");
+ return (-1);
+}