non_blocking.c

[詳解]

/*++
/* NAME
/*  non_blocking 3
/* SUMMARY
/*  set/clear non-blocking flag
/* SYNOPSIS
/*  #include <iostuff.h>
/*
/*  int non_blocking(int fd, int on)
/* DESCRIPTION
/*  the \fInon_blocking\fR() function manipulates the non-blocking
/*  flag for the specified open file, and returns the old setting.
/*
/*  Arguments:
/* .IP fd
/*  A file descriptor.
/* .IP on
/*  For non-blocking I/O, specify a non-zero value (or use the
/*  NON_BLOCKING constant); for blocking I/O, specify zero
/*  (or use the BLOCKING constant).
/*
/*  The result is non-zero when the non-blocking flag was enabled.
/* DIAGNOSTICS
/*  All errors are fatal.
/* 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 interfaces. */

#include "sys_defs.h"
#include <fcntl.h>

/* Utility library. */

#include "msg.h"
#include "iostuff.h"

/* Backwards compatibility */
#ifndef O_NONBLOCK
#define PATTERN FNDELAY
#else
#define PATTERN O_NONBLOCK
#endif

/* non_blocking - set/clear non-blocking flag */

int     non_blocking(fd, on)
int     fd;
int     on;
{
    int     flags;

    if ((flags = fcntl(fd, F_GETFL, 0)) < 0)
    msg_fatal("fcntl: get flags: %m");
    if (fcntl(fd, F_SETFL, on ? flags | PATTERN : flags & ~PATTERN) < 0)
    msg_fatal("fcntl: set non-blocking flag %s: %m", on ? "on" : "off");
    return ((flags & PATTERN) != 0);
}