FreeBSD/Linux Kernel Cross Reference
sys/ddb/db_capture.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * 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 "opt_ddb.h"
    
    #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.
     *
     * We enforce an invariant at runtime that buffer sizes are even multiples of
     * the textdump block size, which is a design choice that we might want to
     * reconsider.
     */
    static MALLOC_DEFINE(M_DDB_CAPTURE, "ddb_capture", "DDB capture buffer");
    
    #ifndef DDB_CAPTURE_DEFAULTBUFSIZE
    #define DDB_CAPTURE_DEFAULTBUFSIZE      48*1024
    #endif
    #ifndef DDB_CAPTURE_MAXBUFSIZE
    #define DDB_CAPTURE_MAXBUFSIZE  5*1024*1024
    #endif
    #define DDB_CAPTURE_FILENAME    "ddb.txt"       /* Captured DDB output. */
    
    static char *db_capture_buf;
    static u_int db_capture_bufsize = DDB_CAPTURE_DEFAULTBUFSIZE;
    static u_int db_capture_maxbufsize = DDB_CAPTURE_MAXBUFSIZE; /* Read-only. */
    static u_int db_capture_bufoff;         /* Next location to write in buffer. */
    static u_int db_capture_bufpadding;     /* Amount of zero padding. */
    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 | CTLFLAG_MPSAFE, 0,
        "DDB capture options");
    
    SYSCTL_UINT(_debug_ddb_capture, OID_AUTO, bufoff, 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");
    
    SYSCTL_INT(_debug_ddb_capture, OID_AUTO, inprogress, CTLFLAG_RD,
        &db_capture_inprogress, 0, "DDB output capture in progress");
    
    /*
    * Boot-time allocation of the DDB capture buffer, if any.  Force all buffer
    * sizes, including the maximum size, to be rounded to block sizes.
    */
   static void
   db_capture_sysinit(__unused void *dummy)
   {
   
           TUNABLE_INT_FETCH("debug.ddb.capture.bufsize", &db_capture_bufsize);
           db_capture_maxbufsize = roundup(db_capture_maxbufsize,
               TEXTDUMP_BLOCKSIZE);
           db_capture_bufsize = roundup(db_capture_bufsize, TEXTDUMP_BLOCKSIZE);
           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_DDB_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);
           size = roundup(size, TEXTDUMP_BLOCKSIZE);
           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_DDB_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_DDB_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 | CTLFLAG_MPSAFE, 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 | CTLFLAG_MPSAFE, 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;
   }
   
   /*
    * Zero out any bytes left in the last block of the DDB capture buffer.  This
    * is run shortly before writing the blocks to disk, rather than when output
    * capture is stopped, in order to avoid injecting nul's into the middle of
    * output.
    */
   static void
   db_capture_zeropad(void)
   {
           u_int len;
   
           len = min(TEXTDUMP_BLOCKSIZE, (db_capture_bufsize -
               db_capture_bufoff) % TEXTDUMP_BLOCKSIZE);
           bzero(db_capture_buf + db_capture_bufoff, len);
           db_capture_bufpadding = len;
   }
   
   /*
    * Reset capture state, which flushes buffers.
    */
   static void
   db_capture_reset(void)
   {
   
           db_capture_inprogress = 0;
           db_capture_bufoff = 0;
           db_capture_bufpadding = 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--real work is deferred to db_capture_dump,
    * which executes outside of the DDB context.  We don't zero pad here because
    * capture may be started again before the dump takes place.
    */
   static void
   db_capture_stop(void)
   {
   
           if (db_capture_inprogress == 0) {
                   db_printf("Capture not started\n");
                   return;
           }
           db_capture_inprogress = 0;
   }
   
   /*
    * Dump DDB(4) captured output (and resets capture buffers).
    */
   void
   db_capture_dump(struct dumperinfo *di)
   {
           u_int offset;
   
           if (db_capture_bufoff == 0)
                   return;
   
           db_capture_zeropad();
           textdump_mkustar(textdump_block_buffer, DDB_CAPTURE_FILENAME,
               db_capture_bufoff);
           (void)textdump_writenextblock(di, textdump_block_buffer);
           for (offset = 0; offset < db_capture_bufoff + db_capture_bufpadding;
               offset += TEXTDUMP_BLOCKSIZE)
                   (void)textdump_writenextblock(di, db_capture_buf + offset);
           db_capture_bufoff = 0;
           db_capture_bufpadding = 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, bool 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();
   }

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