Add a new DDB(4) facility, output capture. Input and output from DDB may be

captured to a memory buffer for later inspection using sysctl(8), or in the
future, to a textdump.

A new DDB command, "capture", is added, which accepts arguments "on", "off",
"reset", and "status".

A new DDB sysctl tree, debug.ddb.capture, is added, which can be used to
resize the capture buffer and extract buffer contents.

MFC after:	3 months

sys/conf/files

@@ -350,6 +350,7 @@ crypto/sha2/sha2.c		optional crypto | geom_bde | ipsec | random | \
 					 sctp
 ddb/db_access.c			optional	ddb
 ddb/db_break.c			optional	ddb
+ddb/db_capture.c		optional	ddb
 ddb/db_command.c		optional	ddb
 ddb/db_examine.c		optional	ddb
 ddb/db_expr.c			optional	ddb

sys/ddb/db_capture.c

@@ -0,0 +1,301 @@
+/*-
+ * Copyright (c) 2007 Robert N. M. Watson
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * DDB capture support: capture kernel debugger output into a fixed-size
+ * buffer for later dumping to disk or extraction from user space.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/conf.h>
+#include <sys/kernel.h>
+#include <sys/kerneldump.h>
+#include <sys/malloc.h>
+#include <sys/msgbuf.h>
+#include <sys/priv.h>
+#include <sys/sx.h>
+#include <sys/sysctl.h>
+#include <sys/systm.h>
+
+#include <ddb/ddb.h>
+#include <ddb/db_lex.h>
+
+/*
+ * While it would be desirable to use a small block-sized buffer and dump
+ * incrementally to disk in fixed-size blocks, it's not possible to enter
+ * kernel dumper routines without restarting the kernel, which is undesirable
+ * in the midst of debugging.  Instead, we maintain a large static global
+ * buffer that we fill from DDB's output routines.
+ */
+static MALLOC_DEFINE(M_DB_CAPTURE, "db_capture", "DDB capture buffer");
+
+#define	DB_CAPTURE_DEFAULTBUFSIZE	48*1024
+#define	DB_CAPTURE_MAXBUFSIZE	512*1024
+
+static char *db_capture_buf;
+static u_int db_capture_bufsize = DB_CAPTURE_DEFAULTBUFSIZE;
+static u_int db_capture_maxbufsize = DB_CAPTURE_MAXBUFSIZE; /* Read-only. */
+static u_int db_capture_bufoff;		/* Next location to write in buffer. */
+static int db_capture_inpager;		/* Suspend capture in pager. */
+static int db_capture_inprogress;	/* DDB capture currently in progress. */
+
+struct sx db_capture_sx;		/* Lock against user thread races. */
+SX_SYSINIT(db_capture_sx, &db_capture_sx, "db_capture_sx");
+
+static SYSCTL_NODE(_debug_ddb, OID_AUTO, capture, CTLFLAG_RW, 0,
+    "DDB capture options");
+
+SYSCTL_UINT(_debug_ddb_capture, OID_AUTO, bytes, CTLFLAG_RD,
+    &db_capture_bufoff, 0, "Bytes of data in DDB capture buffer");
+
+SYSCTL_UINT(_debug_ddb_capture, OID_AUTO, maxbufsize, CTLFLAG_RD,
+    &db_capture_maxbufsize, 0,
+    "Maximum value for debug.ddb.capture.bufsize");
+
+/*
+ * Boot-time allocation of the DDB capture buffer, if any.
+ */
+static void
+db_capture_sysinit(__unused void *dummy)
+{
+
+	TUNABLE_INT_FETCH("debug.ddb.capture.bufsize", &db_capture_bufsize);
+	if (db_capture_bufsize > DB_CAPTURE_MAXBUFSIZE)
+		db_capture_bufsize = DB_CAPTURE_MAXBUFSIZE;
+
+	if (db_capture_bufsize != 0)
+		db_capture_buf = malloc(db_capture_bufsize, M_DB_CAPTURE,
+		    M_WAITOK);
+}
+SYSINIT(db_capture, SI_SUB_DDB_SERVICES, SI_ORDER_ANY, db_capture_sysinit,
+    NULL);
+
+/*
+ * Run-time adjustment of the capture buffer.
+ */
+static int
+sysctl_debug_ddb_capture_bufsize(SYSCTL_HANDLER_ARGS)
+{
+	u_int len, size;
+	char *buf;
+	int error;
+
+	size = db_capture_bufsize;
+	error = sysctl_handle_int(oidp, &size, 0, req);
+	if (error || req->newptr == NULL)
+		return (error);
+	if (size > DB_CAPTURE_MAXBUFSIZE)
+		return (EINVAL);
+
+	sx_xlock(&db_capture_sx);
+	if (size != 0) {
+		/*
+		 * Potentially the buffer is quite large, so if we can't
+		 * allocate it, fail rather than waiting.
+		 */
+		buf = malloc(size, M_DB_CAPTURE, M_NOWAIT);
+		if (buf == NULL) {
+			sx_xunlock(&db_capture_sx);
+			return (ENOMEM);
+		}
+		len = min(db_capture_bufoff, size);
+	} else {
+		buf = NULL;
+		len = 0;
+	}
+	if (db_capture_buf != NULL && buf != NULL)
+		bcopy(db_capture_buf, buf, len);
+	if (db_capture_buf != NULL)
+		free(db_capture_buf, M_DB_CAPTURE);
+	db_capture_bufoff = len;
+	db_capture_buf = buf;
+	db_capture_bufsize = size;
+	sx_xunlock(&db_capture_sx);
+
+	KASSERT(db_capture_bufoff <= db_capture_bufsize,
+	    ("sysctl_debug_ddb_capture_bufsize: bufoff > bufsize"));
+	KASSERT(db_capture_bufsize <= DB_CAPTURE_MAXBUFSIZE,
+	    ("sysctl_debug_ddb_capture_maxbufsize: bufsize > maxbufsize"));
+
+	return (0);
+}
+SYSCTL_PROC(_debug_ddb_capture, OID_AUTO, bufsize, CTLTYPE_UINT|CTLFLAG_RW,
+    0, 0, sysctl_debug_ddb_capture_bufsize, "IU",
+    "Size of DDB capture buffer");
+
+/*
+ * Sysctl to read out the capture buffer from userspace.  We require
+ * privilege as sensitive process/memory information may be accessed.
+ */
+static int
+sysctl_debug_ddb_capture_data(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	char ch;
+
+	error = priv_check(req->td, PRIV_DDB_CAPTURE);
+	if (error)
+		return (error);
+
+	sx_slock(&db_capture_sx);
+	error = SYSCTL_OUT(req, db_capture_buf, db_capture_bufoff);
+	sx_sunlock(&db_capture_sx);
+	if (error)
+		return (error);
+	ch = '\0';
+	return (SYSCTL_OUT(req, &ch, sizeof(ch)));
+}
+SYSCTL_PROC(_debug_ddb_capture, OID_AUTO, data, CTLTYPE_STRING | CTLFLAG_RD,
+    NULL, 0, sysctl_debug_ddb_capture_data, "A", "DDB capture data");
+
+/*
+ * Routines for capturing DDB output into a fixed-size buffer.  These are
+ * invoked from DDB's input and output routines.  If we hit the limit on the
+ * buffer, we simply drop further data.
+ */
+void
+db_capture_write(char *buffer, u_int buflen)
+{
+	u_int len;
+
+	if (db_capture_inprogress == 0 || db_capture_inpager)
+		return;
+	len = min(buflen, db_capture_bufsize - db_capture_bufoff);
+	bcopy(buffer, db_capture_buf + db_capture_bufoff, len);
+	db_capture_bufoff += len;
+
+	KASSERT(db_capture_bufoff <= db_capture_bufsize,
+	    ("db_capture_write: bufoff > bufsize"));
+}
+
+void
+db_capture_writech(char ch)
+{
+
+	return (db_capture_write(&ch, sizeof(ch)));
+}
+
+void
+db_capture_enterpager(void)
+{
+
+	db_capture_inpager = 1;
+}
+
+void
+db_capture_exitpager(void)
+{
+
+	db_capture_inpager = 0;
+}
+
+/*
+ * Reset capture state, which flushes buffers.
+ */
+static void
+db_capture_reset(void)
+{
+
+	db_capture_inprogress = 0;
+	db_capture_bufoff = 0;
+}
+
+/*
+ * Start capture.  Only one session is allowed at any time, but we may
+ * continue a previous session, so the buffer isn't reset.
+ */
+static void
+db_capture_start(void)
+{
+
+	if (db_capture_inprogress) {
+		db_printf("Capture already started\n");
+		return;
+	}
+	db_capture_inprogress = 1;
+}
+
+/*
+ * Terminate DDB output capture.
+ */
+static void
+db_capture_stop(void)
+{
+
+	if (db_capture_inprogress == 0) {
+		db_printf("Capture not started\n");
+		return;
+	}
+	db_capture_inprogress = 0;
+}
+
+/*-
+ * DDB(4) command to manage capture:
+ *
+ * capture on          - start DDB output capture
+ * capture off         - stop DDB output capture
+ * capture reset       - reset DDB capture buffer (also stops capture)
+ * capture status      - print DDB output capture status
+ */
+static void
+db_capture_usage(void)
+{
+
+	db_error("capture [on|off|reset|status]\n");
+}
+
+void
+db_capture_cmd(db_expr_t addr, boolean_t have_addr, db_expr_t count,
+    char *modif)
+{
+	int t;
+
+	t = db_read_token();
+	if (t != tIDENT) {
+		db_capture_usage();
+		return;
+	}
+	if (db_read_token() != tEOL)
+		db_error("?\n");
+	if (strcmp(db_tok_string, "on") == 0)
+		db_capture_start();
+	else if (strcmp(db_tok_string, "off") == 0)
+		db_capture_stop();
+	else if (strcmp(db_tok_string, "reset") == 0)
+		db_capture_reset();
+	else if (strcmp(db_tok_string, "status") == 0) {
+		db_printf("%u/%u bytes used\n", db_capture_bufoff,
+		    db_capture_bufsize);
+		if (db_capture_inprogress)
+			db_printf("capture is on\n");
+		else
+			db_printf("capture is off\n");
+	} else
+		db_capture_usage();
+}

sys/ddb/db_command.c

@@ -141,6 +141,7 @@ static struct command db_commands[] = {
 	{ "kill",	db_kill,		CS_OWN,	0 },
 	{ "watchdog",	db_watchdog,		0,	0 },
 	{ "thread",	db_set_thread,		CS_OWN,	0 },
+	{ "capture",	db_capture_cmd,		CS_OWN,	0 },
 	{ (char *)0, }
 };
 

sys/ddb/db_input.c

@@ -323,6 +323,7 @@ db_readline(lstart, lsize)
 	while (!db_inputchar(cngetc()))
 	    continue;
 
+	db_capture_write(lstart, db_le - db_lbuf_start);
 	db_printf("\n");	/* synch output position */
 	*db_le = 0;
 

sys/ddb/db_main.c

@@ -36,6 +36,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/pcpu.h>
 #include <sys/proc.h>
 #include <sys/reboot.h>
+#include <sys/sysctl.h>
 
 #include <machine/kdb.h>
 #include <machine/pcb.h>
@@ -45,6 +46,8 @@ __FBSDID("$FreeBSD$");
 #include <ddb/db_command.h>
 #include <ddb/db_sym.h>
 
+SYSCTL_NODE(_debug, OID_AUTO, ddb, CTLFLAG_RW, 0, "DDB settings");
+
 static dbbe_init_f db_init;
 static dbbe_trap_f db_trap;
 static dbbe_trace_f db_trace_self_wrapper;

sys/ddb/db_output.c

@@ -90,11 +90,13 @@ db_force_whitespace()
 	    if (next_tab <= db_output_position) {
 		while (last_print < next_tab) { /* DON'T send a tab!!! */
 			cnputc(' ');
+			db_capture_writech(' ');
 			last_print++;
 		}
 	    }
 	    else {
 		cnputc(' ');
+		db_capture_writech(' ');
 		last_print++;
 	    }
 	}
@@ -137,12 +139,14 @@ db_putchar(c, arg)
 	     */
 	    db_force_whitespace();
 	    cnputc(c);
+	    db_capture_writech(c);
 	    db_output_position++;
 	    db_last_non_space = db_output_position;
 	}
 	else if (c == '\n') {
 	    /* Newline */
 	    cnputc(c);
+	    db_capture_writech(c);
 	    db_output_position = 0;
 	    db_last_non_space = 0;
 	    db_check_interrupt();
@@ -155,6 +159,7 @@ db_putchar(c, arg)
 	else if (c == '\r') {
 	    /* Return */
 	    cnputc(c);
+	    db_capture_writech(c);
 	    db_output_position = 0;
 	    db_last_non_space = 0;
 	    db_check_interrupt();
@@ -170,6 +175,7 @@ db_putchar(c, arg)
 	else if (c == '\007') {
 	    /* bell */
 	    cnputc(c);
+	    /* No need to beep in a log: db_capture_writech(c); */
 	}
 	/* other characters are assumed non-printing */
 }
@@ -206,6 +212,7 @@ db_pager(void)
 {
 	int c, done;
 
+	db_capture_enterpager();
 	db_printf("--More--\r");
 	done = 0;
 	while (!done) {
@@ -249,6 +256,7 @@ db_pager(void)
 	db_force_whitespace();
 	db_printf("\r");
 	db_newlines = 0;
+	db_capture_exitpager();
 }
 
 /*

sys/ddb/ddb.h

@@ -37,6 +37,10 @@
 #ifndef _DDB_DDB_H_
 #define	_DDB_DDB_H_
 
+#ifdef SYSCTL_DECL
+SYSCTL_DECL(_debug_ddb);
+#endif
+
 #include <machine/db_machdep.h>		/* type definitions */
 
 #ifndef DB_MAXARGS
@@ -126,6 +130,7 @@ int		db_value_of_name(const char *name, db_expr_t *valuep);
 int		db_write_bytes(vm_offset_t addr, size_t size, char *data);
 
 db_cmdfcn_t	db_breakpoint_cmd;
+db_cmdfcn_t	db_capture_cmd;
 db_cmdfcn_t	db_continue_cmd;
 db_cmdfcn_t	db_delete_cmd;
 db_cmdfcn_t	db_deletehwatch_cmd;
@@ -168,4 +173,14 @@ struct command {
 	struct command_table *more; /* another level of command */
 };
 
+/*
+ * Interface between DDB and the DDB output capture facility.
+ */
+struct dumperinfo;
+void	db_capture_dump(struct dumperinfo *di);
+void	db_capture_enterpager(void);
+void	db_capture_exitpager(void);
+void	db_capture_write(char *buffer, u_int buflen);
+void	db_capture_writech(char ch);
+
 #endif /* !_DDB_DDB_H_ */