msg_output.c revision 1.3 
1/*	$NetBSD: msg_output.c,v 1.3 2020/03/18 19:05:21 christos Exp $	*/
2
3/*++
4/* NAME
5/*	msg_output 3
6/* SUMMARY
7/*	diagnostics output management
8/* SYNOPSIS
9/*	#include <msg_output.h>
10/*
11/*	typedef void (*MSG_OUTPUT_FN)(int level, char *text)
12/*
13/*	void	msg_output(output_fn)
14/*	MSG_OUTPUT_FN output_fn;
15/*
16/*	void	msg_printf(level, format, ...)
17/*	int	level;
18/*	const char *format;
19/*
20/*	void	msg_vprintf(level, format, ap)
21/*	int	level;
22/*	const char *format;
23/*	va_list ap;
24/* DESCRIPTION
25/*	This module implements low-level output management for the
26/*	msg(3) diagnostics interface.
27/*
28/*	msg_output() registers an output handler for the diagnostics
29/*	interface. An application can register multiple output handlers.
30/*	Output handlers are called in the specified order.
31/*	An output handler takes as arguments a severity level (MSG_INFO,
32/*	MSG_WARN, MSG_ERROR, MSG_FATAL, MSG_PANIC, monotonically increasing
33/*	integer values ranging from 0 to MSG_LAST) and pre-formatted,
34/*	sanitized, text in the form of a null-terminated string.
35/*
36/*	msg_printf() and msg_vprintf() format their arguments, sanitize the
37/*	result, and call the output handlers registered with msg_output().
38/*
39/*	msg_text() copies a pre-formatted text, sanitizes the result, and
40/*	calls the output handlers registered with msg_output().
41/* REENTRANCY
42/* .ad
43/* .fi
44/*	The above output routines are protected against ordinary
45/*	recursive calls and against re-entry by signal
46/*	handlers, with the following limitations:
47/* .IP \(bu
48/*	The signal handlers must never return. In other words, the
49/*	signal handlers must do one or more of the following: call
50/*	_exit(), kill the process with a signal, and permanently
51/*	block the process.
52/* .IP \(bu
53/*	The signal handlers must call the above output routines not
54/*	until after msg_output() completes initialization, and not
55/*	until after the first formatted output to a VSTRING or
56/*	VSTREAM.
57/* .IP \(bu
58/*	Each msg_output() call-back function, and each Postfix or
59/*	system function called by that call-back function, either
60/*	must protect itself against recursive calls and re-entry
61/*	by a terminating signal handler, or it must be called
62/*	exclusively by functions in the msg_output(3) module.
63/* .PP
64/*	When re-entrancy is detected, the requested output operation
65/*	is skipped. This prevents memory corruption of VSTREAM_ERR
66/*	data structures, and prevents deadlock on Linux releases
67/*	that use mutexes within system library routines such as
68/*	syslog(). This protection exists under the condition that
69/*	these specific resources are accessed exclusively via
70/*	msg_output() call-back functions.
71/* LICENSE
72/* .ad
73/* .fi
74/*	The Secure Mailer license must be distributed with this software.
75/* AUTHOR(S)
76/*	Wietse Venema
77/*	IBM T.J. Watson Research
78/*	P.O. Box 704
79/*	Yorktown Heights, NY 10598, USA
80/*
81/*	Wietse Venema
82/*	Google, Inc.
83/*	111 8th Avenue
84/*	New York, NY 10011, USA
85/*--*/
86
87/* System library. */
88
89#include <sys_defs.h>
90#include <stdarg.h>
91#include <errno.h>
92
93/* Utility library. */
94
95#include <mymalloc.h>
96#include <vstring.h>
97#include <vstream.h>
98#include <msg_vstream.h>
99#include <stringops.h>
100#include <percentm.h>
101#include <msg_output.h>
102
103 /*
104  * Global scope, to discourage the compiler from doing smart things.
105  */
106volatile int msg_vprintf_level;
107
108 /*
109  * Private state. Allow one nested call, so that one logging error can be
110  * reported to stderr before bailing out.
111  */
112#define MSG_OUT_NESTING_LIMIT	2
113static MSG_OUTPUT_FN *msg_output_fn = 0;
114static int msg_output_fn_count = 0;
115static VSTRING *msg_buffers[MSG_OUT_NESTING_LIMIT];
116
117/* msg_output - specify output handler */
118
119void    msg_output(MSG_OUTPUT_FN output_fn)
120{
121    int     i;
122
123    /*
124     * Allocate all resources during initialization. This may result in a
125     * recursive call due to memory allocation error.
126     */
127    if (msg_buffers[MSG_OUT_NESTING_LIMIT - 1] == 0) {
128	for (i = 0; i < MSG_OUT_NESTING_LIMIT; i++)
129	    msg_buffers[i] = vstring_alloc(100);
130    }
131
132    /*
133     * We're not doing this often, so avoid complexity and allocate memory
134     * for an exact fit.
135     */
136    if (msg_output_fn_count == 0)
137	msg_output_fn = (MSG_OUTPUT_FN *) mymalloc(sizeof(*msg_output_fn));
138    else
139	msg_output_fn = (MSG_OUTPUT_FN *) myrealloc((void *) msg_output_fn,
140			(msg_output_fn_count + 1) * sizeof(*msg_output_fn));
141    msg_output_fn[msg_output_fn_count++] = output_fn;
142}
143
144/* msg_printf - format text and log it */
145
146void    msg_printf(int level, const char *format,...)
147{
148    va_list ap;
149
150    va_start(ap, format);
151    msg_vprintf(level, format, ap);
152    va_end(ap);
153}
154
155/* msg_vprintf - format text and log it */
156
157void    msg_vprintf(int level, const char *format, va_list ap)
158{
159    int     saved_errno = errno;
160    VSTRING *vp;
161    int     i;
162
163    if (msg_vprintf_level < MSG_OUT_NESTING_LIMIT) {
164	msg_vprintf_level += 1;
165	/* On-the-fly initialization for test programs and startup errors. */
166	if (msg_output_fn_count == 0)
167	    msg_vstream_init("unknown", VSTREAM_ERR);
168	vp = msg_buffers[msg_vprintf_level - 1];
169	/* OK if terminating signal handler hijacks control before next stmt. */
170	vstring_vsprintf(vp, percentm(format, errno), ap);
171	printable(vstring_str(vp), '?');
172	for (i = 0; i < msg_output_fn_count; i++)
173	    msg_output_fn[i] (level, vstring_str(vp));
174	msg_vprintf_level -= 1;
175    }
176    errno = saved_errno;
177}
178