xref: /freebsd/sys/ddb/db_capture.c (revision d6b92ffa) 
1 /*-
2  * Copyright (c) 2007 Robert N. M. Watson
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24  * SUCH DAMAGE.
25  */
26 
27 /*
28  * DDB capture support: capture kernel debugger output into a fixed-size
29  * buffer for later dumping to disk or extraction from user space.
30  */
31 
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
34 
35 #include "opt_ddb.h"
36 
37 #include <sys/param.h>
38 #include <sys/conf.h>
39 #include <sys/kernel.h>
40 #include <sys/kerneldump.h>
41 #include <sys/malloc.h>
42 #include <sys/msgbuf.h>
43 #include <sys/priv.h>
44 #include <sys/sx.h>
45 #include <sys/sysctl.h>
46 #include <sys/systm.h>
47 
48 #include <ddb/ddb.h>
49 #include <ddb/db_lex.h>
50 
51 /*
52  * While it would be desirable to use a small block-sized buffer and dump
53  * incrementally to disk in fixed-size blocks, it's not possible to enter
54  * kernel dumper routines without restarting the kernel, which is undesirable
55  * in the midst of debugging.  Instead, we maintain a large static global
56  * buffer that we fill from DDB's output routines.
57  *
58  * We enforce an invariant at runtime that buffer sizes are even multiples of
59  * the textdump block size, which is a design choice that we might want to
60  * reconsider.
61  */
62 static MALLOC_DEFINE(M_DDB_CAPTURE, "ddb_capture", "DDB capture buffer");
63 
64 #ifndef DDB_CAPTURE_DEFAULTBUFSIZE
65 #define	DDB_CAPTURE_DEFAULTBUFSIZE	48*1024
66 #endif
67 #ifndef DDB_CAPTURE_MAXBUFSIZE
68 #define	DDB_CAPTURE_MAXBUFSIZE	5*1024*1024
69 #endif
70 #define	DDB_CAPTURE_FILENAME	"ddb.txt"	/* Captured DDB output. */
71 
72 static char *db_capture_buf;
73 static u_int db_capture_bufsize = DDB_CAPTURE_DEFAULTBUFSIZE;
74 static u_int db_capture_maxbufsize = DDB_CAPTURE_MAXBUFSIZE; /* Read-only. */
75 static u_int db_capture_bufoff;		/* Next location to write in buffer. */
76 static u_int db_capture_bufpadding;	/* Amount of zero padding. */
77 static int db_capture_inpager;		/* Suspend capture in pager. */
78 static int db_capture_inprogress;	/* DDB capture currently in progress. */
79 
80 struct sx db_capture_sx;		/* Lock against user thread races. */
81 SX_SYSINIT(db_capture_sx, &db_capture_sx, "db_capture_sx");
82 
83 static SYSCTL_NODE(_debug_ddb, OID_AUTO, capture, CTLFLAG_RW, 0,
84     "DDB capture options");
85 
86 SYSCTL_UINT(_debug_ddb_capture, OID_AUTO, bufoff, CTLFLAG_RD,
87     &db_capture_bufoff, 0, "Bytes of data in DDB capture buffer");
88 
89 SYSCTL_UINT(_debug_ddb_capture, OID_AUTO, maxbufsize, CTLFLAG_RD,
90     &db_capture_maxbufsize, 0,
91     "Maximum value for debug.ddb.capture.bufsize");
92 
93 SYSCTL_INT(_debug_ddb_capture, OID_AUTO, inprogress, CTLFLAG_RD,
94     &db_capture_inprogress, 0, "DDB output capture in progress");
95 
96 /*
97  * Boot-time allocation of the DDB capture buffer, if any.  Force all buffer
98  * sizes, including the maximum size, to be rounded to block sizes.
99  */
100 static void
101 db_capture_sysinit(__unused void *dummy)
102 {
103 
104 	TUNABLE_INT_FETCH("debug.ddb.capture.bufsize", &db_capture_bufsize);
105 	db_capture_maxbufsize = roundup(db_capture_maxbufsize,
106 	    TEXTDUMP_BLOCKSIZE);
107 	db_capture_bufsize = roundup(db_capture_bufsize, TEXTDUMP_BLOCKSIZE);
108 	if (db_capture_bufsize > db_capture_maxbufsize)
109 		db_capture_bufsize = db_capture_maxbufsize;
110 	if (db_capture_bufsize != 0)
111 		db_capture_buf = malloc(db_capture_bufsize, M_DDB_CAPTURE,
112 		    M_WAITOK);
113 }
114 SYSINIT(db_capture, SI_SUB_DDB_SERVICES, SI_ORDER_ANY, db_capture_sysinit,
115     NULL);
116 
117 /*
118  * Run-time adjustment of the capture buffer.
119  */
120 static int
121 sysctl_debug_ddb_capture_bufsize(SYSCTL_HANDLER_ARGS)
122 {
123 	u_int len, size;
124 	char *buf;
125 	int error;
126 
127 	size = db_capture_bufsize;
128 	error = sysctl_handle_int(oidp, &size, 0, req);
129 	if (error || req->newptr == NULL)
130 		return (error);
131 	size = roundup(size, TEXTDUMP_BLOCKSIZE);
132 	if (size > db_capture_maxbufsize)
133 		return (EINVAL);
134 	sx_xlock(&db_capture_sx);
135 	if (size != 0) {
136 		/*
137 		 * Potentially the buffer is quite large, so if we can't
138 		 * allocate it, fail rather than waiting.
139 		 */
140 		buf = malloc(size, M_DDB_CAPTURE, M_NOWAIT);
141 		if (buf == NULL) {
142 			sx_xunlock(&db_capture_sx);
143 			return (ENOMEM);
144 		}
145 		len = min(db_capture_bufoff, size);
146 	} else {
147 		buf = NULL;
148 		len = 0;
149 	}
150 	if (db_capture_buf != NULL && buf != NULL)
151 		bcopy(db_capture_buf, buf, len);
152 	if (db_capture_buf != NULL)
153 		free(db_capture_buf, M_DDB_CAPTURE);
154 	db_capture_bufoff = len;
155 	db_capture_buf = buf;
156 	db_capture_bufsize = size;
157 	sx_xunlock(&db_capture_sx);
158 
159 	KASSERT(db_capture_bufoff <= db_capture_bufsize,
160 	    ("sysctl_debug_ddb_capture_bufsize: bufoff > bufsize"));
161 	KASSERT(db_capture_bufsize <= db_capture_maxbufsize,
162 	    ("sysctl_debug_ddb_capture_maxbufsize: bufsize > maxbufsize"));
163 
164 	return (0);
165 }
166 SYSCTL_PROC(_debug_ddb_capture, OID_AUTO, bufsize, CTLTYPE_UINT|CTLFLAG_RW,
167     0, 0, sysctl_debug_ddb_capture_bufsize, "IU",
168     "Size of DDB capture buffer");
169 
170 /*
171  * Sysctl to read out the capture buffer from userspace.  We require
172  * privilege as sensitive process/memory information may be accessed.
173  */
174 static int
175 sysctl_debug_ddb_capture_data(SYSCTL_HANDLER_ARGS)
176 {
177 	int error;
178 	char ch;
179 
180 	error = priv_check(req->td, PRIV_DDB_CAPTURE);
181 	if (error)
182 		return (error);
183 
184 	sx_slock(&db_capture_sx);
185 	error = SYSCTL_OUT(req, db_capture_buf, db_capture_bufoff);
186 	sx_sunlock(&db_capture_sx);
187 	if (error)
188 		return (error);
189 	ch = '\0';
190 	return (SYSCTL_OUT(req, &ch, sizeof(ch)));
191 }
192 SYSCTL_PROC(_debug_ddb_capture, OID_AUTO, data, CTLTYPE_STRING | CTLFLAG_RD,
193     NULL, 0, sysctl_debug_ddb_capture_data, "A", "DDB capture data");
194 
195 /*
196  * Routines for capturing DDB output into a fixed-size buffer.  These are
197  * invoked from DDB's input and output routines.  If we hit the limit on the
198  * buffer, we simply drop further data.
199  */
200 void
201 db_capture_write(char *buffer, u_int buflen)
202 {
203 	u_int len;
204 
205 	if (db_capture_inprogress == 0 || db_capture_inpager)
206 		return;
207 	len = min(buflen, db_capture_bufsize - db_capture_bufoff);
208 	bcopy(buffer, db_capture_buf + db_capture_bufoff, len);
209 	db_capture_bufoff += len;
210 
211 	KASSERT(db_capture_bufoff <= db_capture_bufsize,
212 	    ("db_capture_write: bufoff > bufsize"));
213 }
214 
215 void
216 db_capture_writech(char ch)
217 {
218 
219 	return (db_capture_write(&ch, sizeof(ch)));
220 }
221 
222 void
223 db_capture_enterpager(void)
224 {
225 
226 	db_capture_inpager = 1;
227 }
228 
229 void
230 db_capture_exitpager(void)
231 {
232 
233 	db_capture_inpager = 0;
234 }
235 
236 /*
237  * Zero out any bytes left in the last block of the DDB capture buffer.  This
238  * is run shortly before writing the blocks to disk, rather than when output
239  * capture is stopped, in order to avoid injecting nul's into the middle of
240  * output.
241  */
242 static void
243 db_capture_zeropad(void)
244 {
245 	u_int len;
246 
247 	len = min(TEXTDUMP_BLOCKSIZE, (db_capture_bufsize -
248 	    db_capture_bufoff) % TEXTDUMP_BLOCKSIZE);
249 	bzero(db_capture_buf + db_capture_bufoff, len);
250 	db_capture_bufpadding = len;
251 }
252 
253 /*
254  * Reset capture state, which flushes buffers.
255  */
256 static void
257 db_capture_reset(void)
258 {
259 
260 	db_capture_inprogress = 0;
261 	db_capture_bufoff = 0;
262 	db_capture_bufpadding = 0;
263 }
264 
265 /*
266  * Start capture.  Only one session is allowed at any time, but we may
267  * continue a previous session, so the buffer isn't reset.
268  */
269 static void
270 db_capture_start(void)
271 {
272 
273 	if (db_capture_inprogress) {
274 		db_printf("Capture already started\n");
275 		return;
276 	}
277 	db_capture_inprogress = 1;
278 }
279 
280 /*
281  * Terminate DDB output capture--real work is deferred to db_capture_dump,
282  * which executes outside of the DDB context.  We don't zero pad here because
283  * capture may be started again before the dump takes place.
284  */
285 static void
286 db_capture_stop(void)
287 {
288 
289 	if (db_capture_inprogress == 0) {
290 		db_printf("Capture not started\n");
291 		return;
292 	}
293 	db_capture_inprogress = 0;
294 }
295 
296 /*
297  * Dump DDB(4) captured output (and resets capture buffers).
298  */
299 void
300 db_capture_dump(struct dumperinfo *di)
301 {
302 	u_int offset;
303 
304 	if (db_capture_bufoff == 0)
305 		return;
306 
307 	db_capture_zeropad();
308 	textdump_mkustar(textdump_block_buffer, DDB_CAPTURE_FILENAME,
309 	    db_capture_bufoff);
310 	(void)textdump_writenextblock(di, textdump_block_buffer);
311 	for (offset = 0; offset < db_capture_bufoff + db_capture_bufpadding;
312 	    offset += TEXTDUMP_BLOCKSIZE)
313 		(void)textdump_writenextblock(di, db_capture_buf + offset);
314 	db_capture_bufoff = 0;
315 	db_capture_bufpadding = 0;
316 }
317 
318 /*-
319  * DDB(4) command to manage capture:
320  *
321  * capture on          - start DDB output capture
322  * capture off         - stop DDB output capture
323  * capture reset       - reset DDB capture buffer (also stops capture)
324  * capture status      - print DDB output capture status
325  */
326 static void
327 db_capture_usage(void)
328 {
329 
330 	db_error("capture [on|off|reset|status]\n");
331 }
332 
333 void
334 db_capture_cmd(db_expr_t addr, bool have_addr, db_expr_t count, char *modif)
335 {
336 	int t;
337 
338 	t = db_read_token();
339 	if (t != tIDENT) {
340 		db_capture_usage();
341 		return;
342 	}
343 	if (db_read_token() != tEOL)
344 		db_error("?\n");
345 	if (strcmp(db_tok_string, "on") == 0)
346 		db_capture_start();
347 	else if (strcmp(db_tok_string, "off") == 0)
348 		db_capture_stop();
349 	else if (strcmp(db_tok_string, "reset") == 0)
350 		db_capture_reset();
351 	else if (strcmp(db_tok_string, "status") == 0) {
352 		db_printf("%u/%u bytes used\n", db_capture_bufoff,
353 		    db_capture_bufsize);
354 		if (db_capture_inprogress)
355 			db_printf("capture is on\n");
356 		else
357 			db_printf("capture is off\n");
358 	} else
359 		db_capture_usage();
360 }
361