msg_output.c

[詳解]

/*++
/* NAME
/*  msg_output 3
/* SUMMARY
/*  diagnostics output management
/* SYNOPSIS
/*  #include <msg_output.h>
/*
/*  typedef void (*MSG_OUTPUT_FN)(int level, char *text)
/*
/*  void    msg_output(output_fn)
/*  MSG_OUTPUT_FN output_fn;
/*
/*  void    msg_printf(level, format, ...)
/*  int level;
/*  const char *format;
/*
/*  void    msg_vprintf(level, format, ap)
/*  int level;
/*  const char *format;
/*  va_list ap;
/*
/*  void    msg_text(level, text)
/*  int level;
/*  const char *text;
/* DESCRIPTION
/*  This module implements low-level output management for the
/*  msg(3) diagnostics interface.
/*
/*  msg_output() registers an output handler for the diagnostics
/*  interface. An application can register multiple output handlers.
/*  Output handlers are called in the specified order.
/*  An output handler takes as arguments a severity level (MSG_INFO,
/*  MSG_WARN, MSG_ERROR, MSG_FATAL, MSG_PANIC, monotonically increasing
/*  integer values ranging from 0 to MSG_LAST) and pre-formatted,
/*  sanitized, text in the form of a null-terminated string.
/*
/*  msg_printf() and msg_vprintf() format their arguments, sanitize the
/*  result, and call the output handlers registered with msg_output().
/*
/*  msg_text() copies a pre-formatted text, sanitizes the result, and
/*  calls the output handlers registered with msg_output().
/* REENTRANCY
/* .ad
/* .fi
/*  The above output routines are protected against ordinary
/*  recursive calls and against re-entry by signal
/*  handlers, with the following limitations:
/* .IP \(bu
/*  The signal handlers must never return. In other words, the
/*  signal handlers must do one or more of the following: call
/*  _exit(), kill the process with a signal, and permanently
/*  block the process.
/* .IP \(bu
/*  The signal handlers must call the above output routines not
/*  until after msg_output() completes initialization, and not
/*  until after the first formatted output to a VSTRING or
/*  VSTREAM.
/* .IP \(bu
/*  Each msg_output() call-back function, and each Postfix or
/*  system function called by that call-back function, either
/*  must protect itself against recursive calls and re-entry
/*  by a terminating signal handler, or it must be called
/*  exclusively by functions in the msg_output(3) module.
/* .PP
/*  When re-entrancy is detected, the requested output operation
/*  is skipped. This prevents memory corruption of VSTREAM_ERR
/*  data structures, and prevents deadlock on Linux releases
/*  that use mutexes within system library routines such as
/*  syslog(). This protection exists under the condition that
/*  these specific resources are accessed exclusively via
/*  msg_output() call-back functions.
/* 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 <stdarg.h>
#include <errno.h>

/* Utility library. */

#include <mymalloc.h>
#include <vstring.h>
#include <vstream.h>
#include <msg_vstream.h>
#include <stringops.h>
#include <percentm.h>
#include <msg_output.h>

 /*
  * Global scope, to discourage the compiler from doing smart things.
  */
volatile int msg_vprintf_lock;
volatile int msg_text_lock;

 /*
  * Private state.
  */
static MSG_OUTPUT_FN *msg_output_fn = 0;
static int msg_output_fn_count = 0;
static VSTRING *msg_buffer = 0;

/* msg_output - specify output handler */

void    msg_output(MSG_OUTPUT_FN output_fn)
{

    /*
     * Allocate all resources during initialization.
     */
    if (msg_buffer == 0)
    msg_buffer = vstring_alloc(100);

    /*
     * We're not doing this often, so avoid complexity and allocate memory
     * for an exact fit.
     */
    if (msg_output_fn_count == 0)
    msg_output_fn = (MSG_OUTPUT_FN *) mymalloc(sizeof(*msg_output_fn));
    else
    msg_output_fn = (MSG_OUTPUT_FN *) myrealloc((void *) msg_output_fn,
            (msg_output_fn_count + 1) * sizeof(*msg_output_fn));
    msg_output_fn[msg_output_fn_count++] = output_fn;
}

/* msg_printf - format text and log it */

void    msg_printf(int level, const char *format,...)
{
    va_list ap;

    va_start(ap, format);
    msg_vprintf(level, format, ap);
    va_end(ap);
}

/* msg_vprintf - format text and log it */

void    msg_vprintf(int level, const char *format, va_list ap)
{
    int     saved_errno = errno;

    if (msg_vprintf_lock == 0) {
    msg_vprintf_lock = 1;
    /* On-the-fly initialization for debugging test programs only. */
    if (msg_output_fn_count == 0)
        msg_vstream_init("unknown", VSTREAM_ERR);
    /* OK if terminating signal handler hijacks control before next stmt. */
    vstring_vsprintf(msg_buffer, percentm(format, errno), ap);
    msg_text(level, vstring_str(msg_buffer));
    msg_vprintf_lock = 0;
    }
    errno = saved_errno;
}

/* msg_text - sanitize and log pre-formatted text */

void    msg_text(int level, const char *text)
{
    int     i;

    /*
     * Sanitize the text. Use a private copy if necessary.
     */
    if (msg_text_lock == 0) {
    msg_text_lock = 1;
    /* OK if terminating signal handler hijacks control before next stmt. */
    if (text != vstring_str(msg_buffer))
        vstring_strcpy(msg_buffer, text);
    printable(vstring_str(msg_buffer), '?');
    /* On-the-fly initialization for debugging test programs only. */
    if (msg_output_fn_count == 0)
        msg_vstream_init("unknown", VSTREAM_ERR);
    for (i = 0; i < msg_output_fn_count; i++)
        msg_output_fn[i] (level, vstring_str(msg_buffer));
    msg_text_lock = 0;
    }
}