master_monitor.c

[詳解]

/*++
/* NAME
/*  master_monitor 3
/* SUMMARY
/*  Postfix master - start-up monitoring
/* SYNOPSIS
/*  #include "master.h"
/*
/*  int     master_monitor(time_limit)
/*  int time_limit;
/* DESCRIPTION
/*  master_monitor() forks off a background child process, and
/*  returns in the child. The result value is the file descriptor
/*  on which the child process must write one byte after it
/*  completes successful initialization as a daemon process.
/*
/*  The foreground process waits for the child's completion for
/*  a limited amount of time. It terminates with exit status 0
/*  in case of success, non-zero otherwise.
/* DIAGNOSTICS
/*  Fatal errors: system call failure.
/* BUGS
/* SEE ALSO
/* 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 <signal.h>
#include <unistd.h>
#include <stdlib.h>

/* Utility library. */

#include <msg.h>
#include <iostuff.h>

/* Application-specific. */

#include <master.h>

/* master_monitor - fork off a foreground monitor process */

int     master_monitor(int time_limit)
{
    pid_t   pid;
    int     pipes[2];
    char    buf[1];

    /*
     * Sanity check.
     */
    if (time_limit <= 0)
    msg_panic("master_monitor: bad time limit: %d", time_limit);

    /*
     * Set up the plumbing for child-to-parent communication.
     */
    if (pipe(pipes) < 0)
    msg_fatal("pipe: %m");
    close_on_exec(pipes[0], CLOSE_ON_EXEC);
    close_on_exec(pipes[1], CLOSE_ON_EXEC);

    /*
     * Fork the child, and wait for it to report successful initialization.
     */
    switch (pid = fork()) {
    case -1:
    /* Error. */
    msg_fatal("fork: %m");
    case 0:
    /* Child. Initialize as daemon in the background. */
    close(pipes[0]);
    return (pipes[1]);
    default:
    /* Parent. Monitor the child in the foreground. */
    close(pipes[1]);
    switch (timed_read(pipes[0], buf, 1, time_limit, (void *) 0)) {
    default:
        /* The child process still runs, but something is wrong. */
        (void) kill(pid, SIGKILL);
        /* FALLTHROUGH */
    case 0:
        /* The child process exited prematurely. */
        msg_fatal("daemon initialization failure");
    case 1:
        /* The child process initialized successfully. */
        exit(0);
    }
    }
}