deliver_flock.c

[詳解]

/*++
/* 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);
}