common/mdb/mdb_io.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 2012, Joyent, Inc. All rights reserved.
 * Copyright (c) 2016 by Delphix. All rights reserved.
 */

/*
 * MDB uses its own enhanced standard i/o mechanism for all input and output.
 * This file provides the underpinnings of this mechanism, including the
 * printf-style formatting code, the output pager, and APIs for raw input
 * and output.  This mechanism is used throughout the debugger for everything
 * from simple sprintf and printf-style formatting, to input to the lexer
 * and parser, to raw file i/o for reading ELF files.  In general, we divide
 * our i/o implementation into two parts:
 *
 * (1) An i/o buffer (mdb_iob_t) provides buffered read or write capabilities,
 * as well as access to formatting and the ability to invoke a pager.  The
 * buffer is constructed explicitly for use in either reading or writing; it
 * may not be used for both simultaneously.
 *
 * (2) Each i/o buffer is associated with an underlying i/o backend (mdb_io_t).
 * The backend provides, through an ops-vector, equivalents for the standard
 * read, write, lseek, ioctl, and close operations.  In addition, the backend
 * can provide an IOP_NAME entry point for returning a name for the backend,
 * IOP_LINK and IOP_UNLINK entry points that are called when the backend is
 * connected or disconnected from an mdb_iob_t, and an IOP_SETATTR entry point
 * for manipulating terminal attributes.
 *
 * The i/o objects themselves are reference counted so that more than one i/o
 * buffer may make use of the same i/o backend.  In addition, each buffer
 * provides the ability to push or pop backends to interpose on input or output
 * behavior.  We make use of this, for example, to implement interactive
 * session logging.  Normally, the stdout iob has a backend that is either
 * file descriptor 1, or a terminal i/o backend associated with the tty.
 * However, we can push a log i/o backend on top that multiplexes stdout to
 * the original back-end and another backend that writes to a log file.  The
 * use of i/o backends is also used for simplifying tasks such as making
 * lex and yacc read from strings for mdb_eval(), and making our ELF file
 * processing code read executable "files" from a crash dump via kvm_uread.
 *
 * Additionally, the formatting code provides auto-wrap and indent facilities
 * that are necessary for compatibility with adb macro formatting.  In auto-
 * wrap mode, the formatting code examines each new chunk of output to determine
 * if it will fit on the current line.  If not, instead of having the chunk
 * divided between the current line of output and the next, the auto-wrap
 * code will automatically output a newline, auto-indent the next line,
 * and then continue.  Auto-indent is implemented by simply prepending a number
 * of blanks equal to iob_margin to the start of each line.  The margin is
 * inserted when the iob is created, and following each flush of the buffer.
 */

#include <sys/types.h>
#include <sys/termios.h>
#include <stdarg.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#include <mdb/mdb_types.h>
#include <mdb/mdb_argvec.h>
#include <mdb/mdb_stdlib.h>
#include <mdb/mdb_string.h>
#include <mdb/mdb_target.h>
#include <mdb/mdb_signal.h>
#include <mdb/mdb_debug.h>
#include <mdb/mdb_io_impl.h>
#include <mdb/mdb_modapi.h>
#include <mdb/mdb_demangle.h>
#include <mdb/mdb_err.h>
#include <mdb/mdb_nv.h>
#include <mdb/mdb_frame.h>
#include <mdb/mdb_lex.h>
#include <mdb/mdb.h>

/*
 * Define list of possible integer sizes for conversion routines:
 */
typedef enum {
    SZ_SHORT,       /* format %h? */
    SZ_INT,         /* format %? */
    SZ_LONG,        /* format %l? */
    SZ_LONGLONG     /* format %ll? */
} intsize_t;

/*
 * The iob snprintf family of functions makes use of a special "sprintf
 * buffer" i/o backend in order to provide the appropriate snprintf semantics.
 * This structure is maintained as the backend-specific private storage,
 * and its use is described in more detail below (see spbuf_write()).
 */
typedef struct {
    char *spb_buf;      /* pointer to underlying buffer */
    size_t spb_bufsiz;  /* length of underlying buffer */
    size_t spb_total;   /* total of all bytes passed via IOP_WRITE */
} spbuf_t;

/*
 * Define VA_ARG macro for grabbing the next datum to format for the printf
 * family of functions.  We use VA_ARG so that we can support two kinds of
 * argument lists: the va_list type supplied by <stdarg.h> used for printf and
 * vprintf, and an array of mdb_arg_t structures, which we expect will be
 * either type STRING or IMMEDIATE.  The vec_arg function takes care of
 * handling the mdb_arg_t case.
 */

typedef enum {
    VAT_VARARGS,        /* va_list is a va_list */
    VAT_ARGVEC      /* va_list is a const mdb_arg_t[] in disguise */
} vatype_t;

typedef struct {
    vatype_t val_type;
    union {
        va_list _val_valist;
        const mdb_arg_t *_val_argv;
    } _val_u;
} varglist_t;

#define val_valist  _val_u._val_valist
#define val_argv    _val_u._val_argv

#define VA_ARG(ap, type) ((ap->val_type == VAT_VARARGS) ? \
    va_arg(ap->val_valist, type) : (type)vec_arg(&ap->val_argv))
#define VA_PTRARG(ap) ((ap->val_type == VAT_VARARGS) ? \
    (void *)va_arg(ap->val_valist, uintptr_t) : \
    (void *)(uintptr_t)vec_arg(&ap->val_argv))

/*
 * Define macro for converting char constant to Ctrl-char equivalent:
 */
#ifndef CTRL
#define CTRL(c) ((c) & 0x01f)
#endif

/*
 * Define macro for determining if we should automatically wrap to the next
 * line of output, based on the amount of consumed buffer space and the
 * specified size of the next thing to be inserted (n).
 */
#define IOB_WRAPNOW(iob, n) \
    (((iob)->iob_flags & MDB_IOB_AUTOWRAP) && ((iob)->iob_nbytes != 0) && \
    ((n) + (iob)->iob_nbytes > (iob)->iob_cols))

/*
 * Define prompt string and string to erase prompt string for iob_pager
 * function, which is invoked if the pager is enabled on an i/o buffer
 * and we're about to print a line which would be the last on the screen.
 */

static const char io_prompt[] = ">> More [<space>, <cr>, q, n, c, a] ? ";
static const char io_perase[] = "                                      ";

static const char io_pbcksp[] =
/*CSTYLED*/
"\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b";

static const size_t io_promptlen = sizeof (io_prompt) - 1;
static const size_t io_peraselen = sizeof (io_perase) - 1;
static const size_t io_pbcksplen = sizeof (io_pbcksp) - 1;

static ssize_t
iob_write(mdb_iob_t *iob, mdb_io_t *io, const void *buf, size_t n)
{
    ssize_t resid = n;
    ssize_t len;

    while (resid != 0) {
        if ((len = IOP_WRITE(io, buf, resid)) <= 0)
            break;

        buf = (char *)buf + len;
        resid -= len;
    }

    /*
     * Note that if we had a partial write before an error, we still want
     * to return the fact something was written.  The caller will get an
     * error next time it tries to write anything.
     */
    if (resid == n && n != 0) {
        iob->iob_flags |= MDB_IOB_ERR;
        return (-1);
    }

    return (n - resid);
}

static ssize_t
iob_read(mdb_iob_t *iob, mdb_io_t *io)
{
    ssize_t len;

    ASSERT(iob->iob_nbytes == 0);
    len = IOP_READ(io, iob->iob_buf, iob->iob_bufsiz);
    iob->iob_bufp = &iob->iob_buf[0];

    switch (len) {
    case -1:
        iob->iob_flags |= MDB_IOB_ERR;
        break;
    case 0:
        iob->iob_flags |= MDB_IOB_EOF;
        break;
    default:
        iob->iob_nbytes = len;
    }

    return (len);
}

/*ARGSUSED*/
static void
iob_winch(int sig, siginfo_t *sip, ucontext_t *ucp, void *data)
{
    siglongjmp(*((sigjmp_buf *)data), sig);
}

static int
iob_pager(mdb_iob_t *iob)
{
    int status = 0;
    sigjmp_buf env;
    uchar_t c;

    mdb_signal_f *termio_winch;
    void *termio_data;
    size_t old_rows;

    if (iob->iob_pgp == NULL || (iob->iob_flags & MDB_IOB_PGCONT))
        return (0);

    termio_winch = mdb_signal_gethandler(SIGWINCH, &termio_data);
    (void) mdb_signal_sethandler(SIGWINCH, iob_winch, &env);

    if (sigsetjmp(env, 1) != 0) {
        /*
         * Reset the cursor back to column zero before printing a new
         * prompt, since its position is unreliable after a SIGWINCH.
         */
        (void) iob_write(iob, iob->iob_pgp, "\r", sizeof (char));
        old_rows = iob->iob_rows;

        /*
         * If an existing SIGWINCH handler was present, call it.  We
         * expect that this will be termio: the handler will read the
         * new window size, and then resize this iob appropriately.
         */
        if (termio_winch != (mdb_signal_f *)NULL)
            termio_winch(SIGWINCH, NULL, NULL, termio_data);

        /*
         * If the window has increased in size, we treat this like a
         * request to fill out the new remainder of the page.
         */
        if (iob->iob_rows > old_rows) {
            iob->iob_flags &= ~MDB_IOB_PGSINGLE;
            iob->iob_nlines = old_rows;
            status = 0;
            goto winch;
        }
    }

    (void) iob_write(iob, iob->iob_pgp, io_prompt, io_promptlen);

    for (;;) {
        if (IOP_READ(iob->iob_pgp, &c, sizeof (c)) != sizeof (c)) {
            status = MDB_ERR_PAGER;
            break;
        }

        switch (c) {
        case 'N':
        case 'n':
        case '\n':
        case '\r':
            iob->iob_flags |= MDB_IOB_PGSINGLE;
            goto done;

        case CTRL('c'):
        case CTRL('\\'):
        case 'Q':
        case 'q':
            mdb_iob_discard(iob);
            status = MDB_ERR_PAGER;
            goto done;

        case 'A':
        case 'a':
            mdb_iob_discard(iob);
            status = MDB_ERR_ABORT;
            goto done;

        case 'C':
        case 'c':
            iob->iob_flags |= MDB_IOB_PGCONT;
            /*FALLTHRU*/

        case ' ':
            iob->iob_flags &= ~MDB_IOB_PGSINGLE;
            goto done;
        }
    }

done:
    (void) iob_write(iob, iob->iob_pgp, io_pbcksp, io_pbcksplen);
winch:
    (void) iob_write(iob, iob->iob_pgp, io_perase, io_peraselen);
    (void) iob_write(iob, iob->iob_pgp, io_pbcksp, io_pbcksplen);
    (void) mdb_signal_sethandler(SIGWINCH, termio_winch, termio_data);

    if ((iob->iob_flags & MDB_IOB_ERR) && status == 0)
        status = MDB_ERR_OUTPUT;

    return (status);
}

static void
iob_indent(mdb_iob_t *iob)
{
    if (iob->iob_nbytes == 0 && iob->iob_margin != 0 &&
        (iob->iob_flags & MDB_IOB_INDENT)) {
        size_t i;

        ASSERT(iob->iob_margin < iob->iob_cols);
        ASSERT(iob->iob_bufp == iob->iob_buf);

        for (i = 0; i < iob->iob_margin; i++)
            *iob->iob_bufp++ = ' ';

        iob->iob_nbytes = iob->iob_margin;
    }
}

static void
iob_unindent(mdb_iob_t *iob)
{
    if (iob->iob_nbytes != 0 && iob->iob_nbytes == iob->iob_margin) {
        const char *p = iob->iob_buf;

        while (p < &iob->iob_buf[iob->iob_margin]) {
            if (*p++ != ' ')
                return;
        }

        iob->iob_bufp = &iob->iob_buf[0];
        iob->iob_nbytes = 0;
    }
}

mdb_iob_t *
mdb_iob_create(mdb_io_t *io, uint_t flags)
{
    mdb_iob_t *iob = mdb_alloc(sizeof (mdb_iob_t), UM_SLEEP);

    iob->iob_buf = mdb_alloc(BUFSIZ, UM_SLEEP);
    iob->iob_bufsiz = BUFSIZ;
    iob->iob_bufp = &iob->iob_buf[0];
    iob->iob_nbytes = 0;
    iob->iob_nlines = 0;
    iob->iob_lineno = 1;
    iob->iob_rows = MDB_IOB_DEFROWS;
    iob->iob_cols = MDB_IOB_DEFCOLS;
    iob->iob_tabstop = MDB_IOB_DEFTAB;
    iob->iob_margin = MDB_IOB_DEFMARGIN;
    iob->iob_flags = flags & ~(MDB_IOB_EOF|MDB_IOB_ERR) | MDB_IOB_AUTOWRAP;
    iob->iob_iop = mdb_io_hold(io);
    iob->iob_pgp = NULL;
    iob->iob_next = NULL;

    IOP_LINK(io, iob);
    iob_indent(iob);
    return (iob);
}

void
mdb_iob_pipe(mdb_iob_t **iobs, mdb_iobsvc_f *rdsvc, mdb_iobsvc_f *wrsvc)
{
    mdb_io_t *pio = mdb_pipeio_create(rdsvc, wrsvc);
    int i;

    iobs[0] = mdb_iob_create(pio, MDB_IOB_RDONLY);
    iobs[1] = mdb_iob_create(pio, MDB_IOB_WRONLY);

    for (i = 0; i < 2; i++) {
        iobs[i]->iob_flags &= ~MDB_IOB_AUTOWRAP;
        iobs[i]->iob_cols = iobs[i]->iob_bufsiz;
    }
}

void
mdb_iob_destroy(mdb_iob_t *iob)
{
    /*
     * Don't flush a pipe, since it may cause a context swith when the
     * other side has already been destroyed.
     */
    if (!mdb_iob_isapipe(iob))
        mdb_iob_flush(iob);

    if (iob->iob_pgp != NULL)
        mdb_io_rele(iob->iob_pgp);

    while (iob->iob_iop != NULL) {
        IOP_UNLINK(iob->iob_iop, iob);
        (void) mdb_iob_pop_io(iob);
    }

    mdb_free(iob->iob_buf, iob->iob_bufsiz);
    mdb_free(iob, sizeof (mdb_iob_t));
}

void
mdb_iob_discard(mdb_iob_t *iob)
{
    iob->iob_bufp = &iob->iob_buf[0];
    iob->iob_nbytes = 0;
}

void
mdb_iob_flush(mdb_iob_t *iob)
{
    int pgerr = 0;

    if (iob->iob_nbytes == 0)
        return; /* Nothing to do if buffer is empty */

    if (iob->iob_flags & MDB_IOB_WRONLY) {
        if (iob->iob_flags & MDB_IOB_PGSINGLE) {
            iob->iob_flags &= ~MDB_IOB_PGSINGLE;
            iob->iob_nlines = 0;
            pgerr = iob_pager(iob);

        } else if (iob->iob_nlines >= iob->iob_rows - 1) {
            iob->iob_nlines = 0;
            if (iob->iob_flags & MDB_IOB_PGENABLE)
                pgerr = iob_pager(iob);
        }

        if (pgerr == 0) {
            /*
             * We only jump out of the dcmd on error if the iob is
             * m_out. Presumably, if a dcmd has opened a special
             * file and is writing to it, it will handle errors
             * properly.
             */
            if (iob_write(iob, iob->iob_iop, iob->iob_buf,
                iob->iob_nbytes) < 0 && iob == mdb.m_out)
                pgerr = MDB_ERR_OUTPUT;
            iob->iob_nlines++;
        }
    }

    iob->iob_bufp = &iob->iob_buf[0];
    iob->iob_nbytes = 0;
    iob_indent(iob);

    if (pgerr)
        longjmp(mdb.m_frame->f_pcb, pgerr);
}

void
mdb_iob_nlflush(mdb_iob_t *iob)
{
    iob_unindent(iob);

    if (iob->iob_nbytes != 0)
        mdb_iob_nl(iob);
    else
        iob_indent(iob);
}

void
mdb_iob_push_io(mdb_iob_t *iob, mdb_io_t *io)
{
    ASSERT(io->io_next == NULL);

    io->io_next = iob->iob_iop;
    iob->iob_iop = mdb_io_hold(io);
}

mdb_io_t *
mdb_iob_pop_io(mdb_iob_t *iob)
{
    mdb_io_t *io = iob->iob_iop;

    if (io != NULL) {
        iob->iob_iop = io->io_next;
        io->io_next = NULL;
        mdb_io_rele(io);
    }

    return (io);
}

void
mdb_iob_resize(mdb_iob_t *iob, size_t rows, size_t cols)
{
    if (cols > iob->iob_bufsiz)
        iob->iob_cols = iob->iob_bufsiz;
    else
        iob->iob_cols = cols != 0 ? cols : MDB_IOB_DEFCOLS;

    iob->iob_rows = rows != 0 ? rows : MDB_IOB_DEFROWS;
}

void
mdb_iob_setpager(mdb_iob_t *iob, mdb_io_t *pgio)
{
    struct winsize winsz;

    if (iob->iob_pgp != NULL) {
        IOP_UNLINK(iob->iob_pgp, iob);
        mdb_io_rele(iob->iob_pgp);
    }

    iob->iob_flags |= MDB_IOB_PGENABLE;
    iob->iob_flags &= ~(MDB_IOB_PGSINGLE | MDB_IOB_PGCONT);
    iob->iob_pgp = mdb_io_hold(pgio);

    IOP_LINK(iob->iob_pgp, iob);

    if (IOP_CTL(pgio, TIOCGWINSZ, &winsz) == 0)
        mdb_iob_resize(iob, (size_t)winsz.ws_row, (size_t)winsz.ws_col);
}

void
mdb_iob_tabstop(mdb_iob_t *iob, size_t tabstop)
{
    iob->iob_tabstop = MIN(tabstop, iob->iob_cols - 1);
}

void
mdb_iob_margin(mdb_iob_t *iob, size_t margin)
{
    iob_unindent(iob);
    iob->iob_margin = MIN(margin, iob->iob_cols - 1);
    iob_indent(iob);
}

void
mdb_iob_setbuf(mdb_iob_t *iob, void *buf, size_t bufsiz)
{
    ASSERT(buf != NULL && bufsiz != 0);

    mdb_free(iob->iob_buf, iob->iob_bufsiz);
    iob->iob_buf = buf;
    iob->iob_bufsiz = bufsiz;

    if (iob->iob_flags & MDB_IOB_WRONLY)
        iob->iob_cols = MIN(iob->iob_cols, iob->iob_bufsiz);
}

void
mdb_iob_clearlines(mdb_iob_t *iob)
{
    iob->iob_flags &= ~(MDB_IOB_PGSINGLE | MDB_IOB_PGCONT);
    iob->iob_nlines = 0;
}

void
mdb_iob_setflags(mdb_iob_t *iob, uint_t flags)
{
    iob->iob_flags |= flags;
    if (flags & MDB_IOB_INDENT)
        iob_indent(iob);
}

void
mdb_iob_clrflags(mdb_iob_t *iob, uint_t flags)
{
    iob->iob_flags &= ~flags;
    if (flags & MDB_IOB_INDENT)
        iob_unindent(iob);
}

uint_t
mdb_iob_getflags(mdb_iob_t *iob)
{
    return (iob->iob_flags);
}

static uintmax_t
vec_arg(const mdb_arg_t **app)
{
    uintmax_t value;

    if ((*app)->a_type == MDB_TYPE_STRING)
        value = (uintmax_t)(uintptr_t)(*app)->a_un.a_str;
    else
        value = (*app)->a_un.a_val;

    (*app)++;
    return (value);
}

static const char *
iob_size2str(intsize_t size)
{
    switch (size) {
    case SZ_SHORT:
        return ("short");
    case SZ_INT:
        return ("int");
    case SZ_LONG:
        return ("long");
    case SZ_LONGLONG:
        return ("long long");
    }
    return ("");
}

/*
 * In order to simplify maintenance of the ::formats display, we provide an
 * unparser for mdb_printf format strings that converts a simple format
 * string with one specifier into a descriptive representation, e.g.
 * mdb_iob_format2str("%llx") returns "hexadecimal long long".
 */
const char *
mdb_iob_format2str(const char *format)
{
    intsize_t size = SZ_INT;
    const char *p;

    static char buf[64];

    buf[0] = '\0';

    if ((p = strchr(format, '%')) == NULL)
        goto done;

fmt_switch:
    switch (*++p) {
    case '0': case '1': case '2': case '3': case '4':
    case '5': case '6': case '7': case '8': case '9':
        while (*p >= '0' && *p <= '9')
            p++;
        p--;
        goto fmt_switch;

    case 'a':
    case 'A':
        return ("symbol");

    case 'b':
        (void) strcpy(buf, "unsigned ");
        (void) strcat(buf, iob_size2str(size));
        (void) strcat(buf, " bitfield");
        break;

    case 'c':
        return ("character");

    case 'd':
    case 'i':
        (void) strcpy(buf, "decimal signed ");
        (void) strcat(buf, iob_size2str(size));
        break;

    case 'e':
    case 'E':
    case 'g':
    case 'G':
        return ("double");

    case 'h':
        size = SZ_SHORT;
        goto fmt_switch;

    case 'H':
        return ("human-readable size");

    case 'I':
        return ("IPv4 address");

    case 'l':
        if (size >= SZ_LONG)
            size = SZ_LONGLONG;
        else
            size = SZ_LONG;
        goto fmt_switch;

    case 'm':
        return ("margin");

    case 'N':
        return ("IPv6 address");

    case 'o':
        (void) strcpy(buf, "octal unsigned ");
        (void) strcat(buf, iob_size2str(size));
        break;

    case 'p':
        return ("pointer");

    case 'q':
        (void) strcpy(buf, "octal signed ");
        (void) strcat(buf, iob_size2str(size));
        break;

    case 'r':
        (void) strcpy(buf, "default radix unsigned ");
        (void) strcat(buf, iob_size2str(size));
        break;

    case 'R':
        (void) strcpy(buf, "default radix signed ");
        (void) strcat(buf, iob_size2str(size));
        break;

    case 's':
        return ("string");

    case 't':
    case 'T':
        return ("tab");

    case 'u':
        (void) strcpy(buf, "decimal unsigned ");
        (void) strcat(buf, iob_size2str(size));
        break;

    case 'x':
    case 'X':
        (void) strcat(buf, "hexadecimal ");
        (void) strcat(buf, iob_size2str(size));
        break;

    case 'Y':
        return ("time_t");

    case '<':
        return ("terminal attribute");

    case '?':
    case '#':
    case '+':
    case '-':
        goto fmt_switch;
    }

done:
    if (buf[0] == '\0')
        (void) strcpy(buf, "text");

    return ((const char *)buf);
}

static const char *
iob_int2str(varglist_t *ap, intsize_t size, int base, uint_t flags, int *zero,
    u_longlong_t *value)
{
    uintmax_t i;

    switch (size) {
    case SZ_LONGLONG:
        if (flags & NTOS_UNSIGNED)
            i = (u_longlong_t)VA_ARG(ap, u_longlong_t);
        else
            i = (longlong_t)VA_ARG(ap, longlong_t);
        break;

    case SZ_LONG:
        if (flags & NTOS_UNSIGNED)
            i = (ulong_t)VA_ARG(ap, ulong_t);
        else
            i = (long)VA_ARG(ap, long);
        break;

    case SZ_SHORT:
        if (flags & NTOS_UNSIGNED)
            i = (ushort_t)VA_ARG(ap, uint_t);
        else
            i = (short)VA_ARG(ap, int);
        break;

    default:
        if (flags & NTOS_UNSIGNED)
            i = (uint_t)VA_ARG(ap, uint_t);
        else
            i = (int)VA_ARG(ap, int);
    }

    *zero = i == 0; /* Return flag indicating if result was zero */
    *value = i; /* Return value retrieved from va_list */

    return (numtostr(i, base, flags));
}

static const char *
iob_time2str(time_t *tmp)
{
    /*
     * ctime(3c) returns a string of the form
     * "Fri Sep 13 00:00:00 1986\n\0".  We turn this into the canonical
     * adb /y format "1986 Sep 13 00:00:00" below.
     */
    const char *src = ctime(tmp);
    static char buf[32];
    char *dst = buf;
    int i;

    if (src == NULL)
        return (numtostr((uintmax_t)*tmp, mdb.m_radix, 0));

    for (i = 20; i < 24; i++)
        *dst++ = src[i]; /* Copy the 4-digit year */

    for (i = 3; i < 19; i++)
        *dst++ = src[i]; /* Copy month, day, and h:m:s */

    *dst = '\0';
    return (buf);
}

static const char *
iob_addr2str(uintptr_t addr)
{
    static char buf[MDB_TGT_SYM_NAMLEN];
    char *name = buf;
    longlong_t offset;
    GElf_Sym sym;

    if (mdb_tgt_lookup_by_addr(mdb.m_target, addr,
        MDB_TGT_SYM_FUZZY, buf, sizeof (buf), &sym, NULL) == -1)
        return (NULL);

    if (mdb.m_demangler != NULL && (mdb.m_flags & MDB_FL_DEMANGLE))
        name = (char *)mdb_dem_convert(mdb.m_demangler, buf);

    /*
     * Here we provide a little cooperation between the %a formatting code
     * and the proc target: if the initial address passed to %a is in fact
     * a PLT address, the proc target's lookup_by_addr code will convert
     * this to the PLT destination (a different address).  We do not want
     * to append a "+/-offset" suffix based on comparison with the query
     * symbol in this case because the proc target has really done a hidden
     * query for us with a different address.  We detect this case by
     * comparing the initial characters of buf to the special PLT= string.
     */
    if (sym.st_value != addr && strncmp(name, "PLT=", 4) != 0) {
        if (sym.st_value > addr)
            offset = -(longlong_t)(sym.st_value - addr);
        else
            offset = (longlong_t)(addr - sym.st_value);

        (void) strcat(name, numtostr(offset, mdb.m_radix,
            NTOS_SIGNPOS | NTOS_SHOWBASE));
    }

    return (name);
}

/*
 * Produce human-readable size, similar in spirit (and identical in output)
 * to libzfs's zfs_nicenum() -- but made significantly more complicated by
 * the constraint that we cannot use snprintf() as an implementation detail.
 * Recall, floating point is verboten in kmdb.
 */
static const char *
iob_bytes2str(varglist_t *ap, intsize_t size)
{
#ifndef _KMDB
    const int sigfig = 3;
    uint64_t orig;
#endif
    uint64_t n;

    static char buf[68], *c;
    int index = 0;
    char u;

    switch (size) {
    case SZ_LONGLONG:
        n = (u_longlong_t)VA_ARG(ap, u_longlong_t);
        break;

    case SZ_LONG:
        n = (ulong_t)VA_ARG(ap, ulong_t);
        break;

    case SZ_SHORT:
        n = (ushort_t)VA_ARG(ap, uint_t);

    default:
        n = (uint_t)VA_ARG(ap, uint_t);
    }

#ifndef _KMDB
    orig = n;
#endif

    while (n >= 1024) {
        n /= 1024;
        index++;
    }

    u = " KMGTPE"[index];
    buf[0] = '\0';

    if (index == 0) {
        return (numtostr(n, 10, 0));
#ifndef _KMDB
    } else if ((orig & ((1ULL << 10 * index) - 1)) == 0) {
#else
    } else {
#endif
        /*
         * If this is an even multiple of the base or we are in an
         * environment where floating point is verboten (i.e., kmdb),
         * always display without any decimal precision.
         */
        (void) strcat(buf, numtostr(n, 10, 0));
#ifndef _KMDB
    } else {
        /*
         * We want to choose a precision that results in the specified
         * number of significant figures (by default, 3).  This is
         * similar to the output that one would get specifying the %.*g
         * format specifier (where the asterisk denotes the number of
         * significant digits), but (1) we include trailing zeros if
         * the there are non-zero digits beyond the number of
         * significant digits (that is, 10241 is '10.0K', not the
         * '10K' that it would be with %.3g) and (2) we never resort
         * to %e notation when the number of digits exceeds the
         * number of significant figures (that is, 1043968 is '1020K',
         * not '1.02e+03K').  This is also made somewhat complicated
         * by the fact that we need to deal with rounding (10239 is
         * '10.0K', not '9.99K'), for which we perform nearest-even
         * rounding.
         */
        double val = (double)orig / (1ULL << 10 * index);
        int i, mag = 1, thresh;

        for (i = 0; i < sigfig - 1; i++)
            mag *= 10;

        for (thresh = mag * 10; mag >= 1; mag /= 10, i--) {
            double mult = val * (double)mag;
            uint32_t v;

            /*
             * Note that we cast mult to a 32-bit value.  We know
             * that val is less than 1024 due to the logic above,
             * and that mag is at most 10^(sigfig - 1).  This means
             * that as long as sigfig is 9 or lower, this will not
             * overflow.  (We perform this cast because it assures
             * that we are never converting a double to a uint64_t,
             * which for some compilers requires a call to a
             * function not guaranteed to be in libstand.)
             */
            if (mult - (double)(uint32_t)mult != 0.5) {
                v = (uint32_t)(mult + 0.5);
            } else {
                /*
                 * We are exactly between integer multiples
                 * of units; perform nearest-even rounding
                 * to be consistent with the behavior of
                 * printf().
                 */
                if ((v = (uint32_t)mult) & 1)
                    v++;
            }

            if (mag == 1) {
                (void) strcat(buf, numtostr(v, 10, 0));
                break;
            }

            if (v < thresh) {
                (void) strcat(buf, numtostr(v / mag, 10, 0));
                (void) strcat(buf, ".");

                c = (char *)numtostr(v % mag, 10, 0);
                i -= strlen(c);

                /*
                 * We need to zero-fill from the right of the
                 * decimal point to the first significant digit
                 * of the fractional component.
                 */
                while (i--)
                    (void) strcat(buf, "0");

                (void) strcat(buf, c);
                break;
            }
        }
#endif
    }

    c = &buf[strlen(buf)];
    *c++ = u;
    *c++ = '\0';

    return (buf);
}

static int
iob_setattr(mdb_iob_t *iob, const char *s, size_t nbytes)
{
    uint_t attr;
    int req;

    if (iob->iob_pgp == NULL)
        return (set_errno(ENOTTY));

    if (nbytes != 0 && *s == '/') {
        req = ATT_OFF;
        nbytes--;
        s++;
    } else
        req = ATT_ON;

    if (nbytes != 1)
        return (set_errno(EINVAL));

    switch (*s) {
    case 's':
        attr = ATT_STANDOUT;
        break;
    case 'u':
        attr = ATT_UNDERLINE;
        break;
    case 'r':
        attr = ATT_REVERSE;
        break;
    case 'b':
        attr = ATT_BOLD;
        break;
    case 'd':
        attr = ATT_DIM;
        break;
    case 'a':
        attr = ATT_ALTCHARSET;
        break;
    default:
        return (set_errno(EINVAL));
    }

    /*
     * We need to flush the current buffer contents before calling
     * IOP_SETATTR because IOP_SETATTR may need to synchronously output
     * terminal escape sequences directly to the underlying device.
     */
    (void) iob_write(iob, iob->iob_iop, iob->iob_buf, iob->iob_nbytes);
    iob->iob_bufp = &iob->iob_buf[0];
    iob->iob_nbytes = 0;

    return (IOP_SETATTR(iob->iob_pgp, req, attr));
}

static void
iob_bits2str(mdb_iob_t *iob, u_longlong_t value, const mdb_bitmask_t *bmp,
    mdb_bool_t altflag)
{
    mdb_bool_t delim = FALSE;
    const char *str;
    size_t width;

    if (bmp == NULL)
        goto out;

    for (; bmp->bm_name != NULL; bmp++) {
        if ((value & bmp->bm_mask) == bmp->bm_bits) {
            width = strlen(bmp->bm_name) + delim;

            if (IOB_WRAPNOW(iob, width))
                mdb_iob_nl(iob);

            if (delim)
                mdb_iob_putc(iob, ',');
            else
                delim = TRUE;

            mdb_iob_puts(iob, bmp->bm_name);
            value &= ~bmp->bm_bits;
        }
    }

out:
    if (altflag == TRUE && (delim == FALSE || value != 0)) {
        str = numtostr(value, 16, NTOS_UNSIGNED | NTOS_SHOWBASE);
        width = strlen(str) + delim;

        if (IOB_WRAPNOW(iob, width))
            mdb_iob_nl(iob);
        if (delim)
            mdb_iob_putc(iob, ',');
        mdb_iob_puts(iob, str);
    }
}

static const char *
iob_inaddr2str(uint32_t addr)
{
    static char buf[INET_ADDRSTRLEN];

    (void) mdb_inet_ntop(AF_INET, &addr, buf, sizeof (buf));

    return (buf);
}

static const char *
iob_ipv6addr2str(void *addr)
{
    static char buf[INET6_ADDRSTRLEN];

    (void) mdb_inet_ntop(AF_INET6, addr, buf, sizeof (buf));

    return (buf);
}

static const char *
iob_getvar(const char *s, size_t len)
{
    mdb_var_t *val;
    char *var;

    if (len == 0) {
        (void) set_errno(EINVAL);
        return (NULL);
    }

    var = strndup(s, len);
    val = mdb_nv_lookup(&mdb.m_nv, var);
    strfree(var);

    if (val == NULL) {
        (void) set_errno(EINVAL);
        return (NULL);
    }

    return (numtostr(mdb_nv_get_value(val), 10, 0));
}

/*
 * The iob_doprnt function forms the main engine of the debugger's output
 * formatting capabilities.  Note that this is NOT exactly compatible with
 * the printf(3S) family, nor is it intended to be so.  We support some
 * extensions and format characters not supported by printf(3S), and we
 * explicitly do NOT provide support for %C, %S, %ws (wide-character strings),
 * do NOT provide for the complete functionality of %f, %e, %E, %g, %G
 * (alternate double formats), and do NOT support %.x (precision specification).
 * Note that iob_doprnt consumes varargs off the original va_list.
 */
static void
iob_doprnt(mdb_iob_t *iob, const char *format, varglist_t *ap)
{
    char c[2] = { 0, 0 };   /* Buffer for single character output */
    const char *p;      /* Current position in format string */
    size_t len;     /* Length of format string to copy verbatim */
    size_t altlen;      /* Length of alternate print format prefix */
    const char *altstr; /* Alternate print format prefix */
    const char *symstr; /* Symbol + offset string */

    u_longlong_t val;   /* Current integer value */
    intsize_t size;     /* Current integer value size */
    uint_t flags;       /* Current flags to pass to iob_int2str */
    size_t width;       /* Current field width */
    int zero;       /* If != 0, then integer value == 0 */

    mdb_bool_t f_alt;   /* Use alternate print format (%#) */
    mdb_bool_t f_altsuff;   /* Alternate print format is a suffix */
    mdb_bool_t f_zfill; /* Zero-fill field (%0) */
    mdb_bool_t f_left;  /* Left-adjust field (%-) */
    mdb_bool_t f_digits;    /* Explicit digits used to set field width */

    union {
        const char *str;
        uint32_t ui32;
        void *ptr;
        time_t tm;
        char c;
        double d;
        long double ld;
    } u;

    ASSERT(iob->iob_flags & MDB_IOB_WRONLY);

    while ((p = strchr(format, '%')) != NULL) {
        /*
         * Output the format string verbatim up to the next '%' char
         */
        if (p != format) {
            len = p - format;
            if (IOB_WRAPNOW(iob, len) && *format != '\n')
                mdb_iob_nl(iob);
            mdb_iob_nputs(iob, format, len);
        }

        /*
         * Now we need to parse the sequence of format characters
         * following the % marker and do the appropriate thing.
         */
        size = SZ_INT;      /* Use normal-sized int by default */
        flags = 0;      /* Clear numtostr() format flags */
        width = 0;      /* No field width limit by default */
        altlen = 0;     /* No alternate format string yet */
        altstr = NULL;      /* No alternate format string yet */

        f_alt = FALSE;      /* Alternate format off by default */
        f_altsuff = FALSE;  /* Alternate format is a prefix */
        f_zfill = FALSE;    /* Zero-fill off by default */
        f_left = FALSE;     /* Left-adjust off by default */
        f_digits = FALSE;   /* No digits for width specified yet */

        fmt_switch:
        switch (*++p) {
        case '0': case '1': case '2': case '3': case '4':
        case '5': case '6': case '7': case '8': case '9':
            if (f_digits == FALSE && *p == '0') {
                f_zfill = TRUE;
                goto fmt_switch;
            }

            if (f_digits == FALSE)
                width = 0; /* clear any other width specifier */

            for (u.c = *p; u.c >= '0' && u.c <= '9'; u.c = *++p)
                width = width * 10 + u.c - '0';

            p--;
            f_digits = TRUE;
            goto fmt_switch;

        case 'a':
            if (size < SZ_LONG)
                size = SZ_LONG; /* Bump to size of uintptr_t */

            u.str = iob_int2str(ap, size, 16,
                NTOS_UNSIGNED | NTOS_SHOWBASE, &zero, &val);

            if ((symstr = iob_addr2str(val)) != NULL)
                u.str = symstr;

            if (f_alt == TRUE) {
                f_altsuff = TRUE;
                altstr = ":";
                altlen = 1;
            }
            break;

        case 'A':
            if (size < SZ_LONG)
                size = SZ_LONG; /* Bump to size of uintptr_t */

            (void) iob_int2str(ap, size, 16,
                NTOS_UNSIGNED, &zero, &val);

            u.str = iob_addr2str(val);

            if (f_alt == TRUE && u.str == NULL)
                u.str = "?";
            break;

        case 'b':
            u.str = iob_int2str(ap, size, 16,
                NTOS_UNSIGNED | NTOS_SHOWBASE, &zero, &val);

            iob_bits2str(iob, val, VA_PTRARG(ap), f_alt);

            format = ++p;
            continue;

        case 'c':
            c[0] = (char)VA_ARG(ap, int);
            u.str = c;
            break;

        case 'd':
        case 'i':
            if (f_alt)
                flags |= NTOS_SHOWBASE;
            u.str = iob_int2str(ap, size, 10, flags, &zero, &val);
            break;

        /* No floating point in kmdb */
#ifndef _KMDB
        case 'e':
        case 'E':
            u.d = VA_ARG(ap, double);
            u.str = doubletos(u.d, 7, *p);
            break;

        case 'g':
        case 'G':
            if (size >= SZ_LONG) {
                u.ld = VA_ARG(ap, long double);
                u.str = longdoubletos(&u.ld, 16,
                    (*p == 'g') ? 'e' : 'E');
            } else {
                u.d = VA_ARG(ap, double);
                u.str = doubletos(u.d, 16,
                    (*p == 'g') ? 'e' : 'E');
            }
            break;
#endif

        case 'h':
            size = SZ_SHORT;
            goto fmt_switch;

        case 'H':
            u.str = iob_bytes2str(ap, size);
            break;

        case 'I':
            u.ui32 = VA_ARG(ap, uint32_t);
            u.str = iob_inaddr2str(u.ui32);
            break;

        case 'l':
            if (size >= SZ_LONG)
                size = SZ_LONGLONG;
            else
                size = SZ_LONG;
            goto fmt_switch;

        case 'm':
            if (iob->iob_nbytes == 0) {
                mdb_iob_ws(iob, (width != 0) ? width :
                    iob->iob_margin);
            }
            format = ++p;
            continue;

        case 'N':
            u.ptr = VA_PTRARG(ap);
            u.str = iob_ipv6addr2str(u.ptr);
            break;

        case 'o':
            u.str = iob_int2str(ap, size, 8, NTOS_UNSIGNED,
                &zero, &val);

            if (f_alt && !zero) {
                altstr = "0";
                altlen = 1;
            }
            break;

        case 'p':
            u.ptr = VA_PTRARG(ap);
            u.str = numtostr((uintptr_t)u.ptr, 16, NTOS_UNSIGNED);
            break;

        case 'q':
            u.str = iob_int2str(ap, size, 8, flags, &zero, &val);

            if (f_alt && !zero) {
                altstr = "0";
                altlen = 1;
            }
            break;

        case 'r':
            if (f_alt)
                flags |= NTOS_SHOWBASE;
            u.str = iob_int2str(ap, size, mdb.m_radix,
                NTOS_UNSIGNED | flags, &zero, &val);
            break;

        case 'R':
            if (f_alt)
                flags |= NTOS_SHOWBASE;
            u.str = iob_int2str(ap, size, mdb.m_radix, flags,
                &zero, &val);
            break;

        case 's':
            u.str = VA_PTRARG(ap);
            if (u.str == NULL)
                u.str = "<NULL>"; /* Be forgiving of NULL */
            break;

        case 't':
            if (width != 0) {
                while (width-- > 0)
                    mdb_iob_tab(iob);
            } else
                mdb_iob_tab(iob);

            format = ++p;
            continue;

        case 'T':
            if (width != 0 && (iob->iob_nbytes % width) != 0) {
                size_t ots = iob->iob_tabstop;
                iob->iob_tabstop = width;
                mdb_iob_tab(iob);
                iob->iob_tabstop = ots;
            }
            format = ++p;
            continue;

        case 'u':
            if (f_alt)
                flags |= NTOS_SHOWBASE;
            u.str = iob_int2str(ap, size, 10,
                flags | NTOS_UNSIGNED, &zero, &val);
            break;

        case 'x':
            u.str = iob_int2str(ap, size, 16, NTOS_UNSIGNED,
                &zero, &val);

            if (f_alt && !zero) {
                altstr = "0x";
                altlen = 2;
            }
            break;

        case 'X':
            u.str = iob_int2str(ap, size, 16,
                NTOS_UNSIGNED | NTOS_UPCASE, &zero, &val);

            if (f_alt && !zero) {
                altstr = "0X";
                altlen = 2;
            }
            break;

        case 'Y':
            u.tm = VA_ARG(ap, time_t);
            u.str = iob_time2str(&u.tm);
            break;

        case '<':
            /*
             * Used to turn attributes on (<b>), to turn them
             * off (</b>), or to print variables (<_var>).
             */
            for (u.str = ++p; *p != '\0' && *p != '>'; p++)
                continue;

            if (*p == '>') {
                size_t paramlen = p - u.str;

                if (paramlen > 0) {
                    if (*u.str == '_') {
                        u.str = iob_getvar(u.str + 1,
                            paramlen - 1);
                        break;
                    } else {
                        (void) iob_setattr(iob, u.str,
                            paramlen);
                    }
                }

                p++;
            }

            format = p;
            continue;

        case '*':
            width = (size_t)(uint_t)VA_ARG(ap, int);
            goto fmt_switch;

        case '%':
            u.str = "%";
            break;

        case '?':
            width = sizeof (uintptr_t) * 2;
            goto fmt_switch;

        case '#':
            f_alt = TRUE;
            goto fmt_switch;

        case '+':
            flags |= NTOS_SIGNPOS;
            goto fmt_switch;

        case '-':
            f_left = TRUE;
            goto fmt_switch;

        default:
            c[0] = p[0];
            u.str = c;
        }

        len = u.str != NULL ? strlen(u.str) : 0;

        if (len + altlen > width)
            width = len + altlen;

        /*
         * If the string and the option altstr won't fit on this line
         * and auto-wrap is set (default), skip to the next line.
         * If the string contains \n, and the \n terminated substring
         * + altstr is shorter than the above, use the shorter lf_len.
         */
        if (u.str != NULL) {
            char *np = strchr(u.str, '\n');
            if (np != NULL) {
                int lf_len = (np - u.str) + altlen;
                if (lf_len < width)
                    width = lf_len;
            }
        }
        if (IOB_WRAPNOW(iob, width))
            mdb_iob_nl(iob);

        /*
         * Optionally add whitespace or zeroes prefixing the value if
         * we haven't filled the minimum width and we're right-aligned.
         */
        if (len < (width - altlen) && f_left == FALSE) {
            mdb_iob_fill(iob, f_zfill ? '0' : ' ',
                width - altlen - len);
        }

        /*
         * Print the alternate string if it's a prefix, and then
         * print the value string itself.
         */
        if (altstr != NULL && f_altsuff == FALSE)
            mdb_iob_nputs(iob, altstr, altlen);
        if (len != 0)
            mdb_iob_nputs(iob, u.str, len);

        /*
         * If we have an alternate string and it's a suffix, print it.
         */
        if (altstr != NULL && f_altsuff == TRUE)
            mdb_iob_nputs(iob, altstr, altlen);

        /*
         * Finally, if we haven't filled the field width and we're
         * left-aligned, pad out the rest with whitespace.
         */
        if ((len + altlen) < width && f_left == TRUE)
            mdb_iob_ws(iob, width - altlen - len);

        format = (*p != '\0') ? ++p : p;
    }

    /*
     * If there's anything left in the format string, output it now
     */
    if (*format != '\0') {
        len = strlen(format);
        if (IOB_WRAPNOW(iob, len) && *format != '\n')
            mdb_iob_nl(iob);
        mdb_iob_nputs(iob, format, len);
    }
}

void
mdb_iob_vprintf(mdb_iob_t *iob, const char *format, va_list alist)
{
    varglist_t ap = { VAT_VARARGS };
    va_copy(ap.val_valist, alist);
    iob_doprnt(iob, format, &ap);
}

void
mdb_iob_aprintf(mdb_iob_t *iob, const char *format, const mdb_arg_t *argv)
{
    varglist_t ap = { VAT_ARGVEC };
    ap.val_argv = argv;
    iob_doprnt(iob, format, &ap);
}

void
mdb_iob_printf(mdb_iob_t *iob, const char *format, ...)
{
    va_list alist;

    va_start(alist, format);
    mdb_iob_vprintf(iob, format, alist);
    va_end(alist);
}

/*
 * In order to handle the sprintf family of functions, we define a special
 * i/o backend known as a "sprintf buf" (or spbuf for short).  This back end
 * provides an IOP_WRITE entry point that concatenates each buffer sent from
 * mdb_iob_flush() onto the caller's buffer until the caller's buffer is
 * exhausted.  We also keep an absolute count of how many bytes were sent to
 * this function during the lifetime of the snprintf call.  This allows us
 * to provide the ability to (1) return the total size required for the given
 * format string and argument list, and (2) support a call to snprintf with a
 * NULL buffer argument with no special case code elsewhere.
 */
static ssize_t
spbuf_write(mdb_io_t *io, const void *buf, size_t buflen)
{
    spbuf_t *spb = io->io_data;

    if (spb->spb_bufsiz != 0) {
        size_t n = MIN(spb->spb_bufsiz, buflen);
        bcopy(buf, spb->spb_buf, n);
        spb->spb_buf += n;
        spb->spb_bufsiz -= n;
    }

    spb->spb_total += buflen;
    return (buflen);
}

static const mdb_io_ops_t spbuf_ops = {
    no_io_read,
    spbuf_write,
    no_io_seek,
    no_io_ctl,
    no_io_close,
    no_io_name,
    no_io_link,
    no_io_unlink,
    no_io_setattr,
    no_io_suspend,
    no_io_resume
};

/*
 * The iob_spb_create function initializes an iob suitable for snprintf calls,
 * a spbuf i/o backend, and the spbuf private data, and then glues these
 * objects together.  The caller (either vsnprintf or asnprintf below) is
 * expected to have allocated the various structures on their stack.
 */
static void
iob_spb_create(mdb_iob_t *iob, char *iob_buf, size_t iob_len,
    mdb_io_t *io, spbuf_t *spb, char *spb_buf, size_t spb_len)
{
    spb->spb_buf = spb_buf;
    spb->spb_bufsiz = spb_len;
    spb->spb_total = 0;

    io->io_ops = &spbuf_ops;
    io->io_data = spb;
    io->io_next = NULL;
    io->io_refcnt = 1;

    iob->iob_buf = iob_buf;
    iob->iob_bufsiz = iob_len;
    iob->iob_bufp = iob_buf;
    iob->iob_nbytes = 0;
    iob->iob_nlines = 0;
    iob->iob_lineno = 1;
    iob->iob_rows = MDB_IOB_DEFROWS;
    iob->iob_cols = iob_len;
    iob->iob_tabstop = MDB_IOB_DEFTAB;
    iob->iob_margin = MDB_IOB_DEFMARGIN;
    iob->iob_flags = MDB_IOB_WRONLY;
    iob->iob_iop = io;
    iob->iob_pgp = NULL;
    iob->iob_next = NULL;
}

/*ARGSUSED*/
ssize_t
null_io_write(mdb_io_t *io, const void *buf, size_t nbytes)
{
    return (nbytes);
}

static const mdb_io_ops_t null_ops = {
    no_io_read,
    null_io_write,
    no_io_seek,
    no_io_ctl,
    no_io_close,
    no_io_name,
    no_io_link,
    no_io_unlink,
    no_io_setattr,
    no_io_suspend,
    no_io_resume
};

mdb_io_t *
mdb_nullio_create(void)
{
    static mdb_io_t null_io = {
        &null_ops,
        NULL,
        NULL,
        1
    };

    return (&null_io);
}

size_t
mdb_iob_vsnprintf(char *buf, size_t nbytes, const char *format, va_list alist)
{
    varglist_t ap = { VAT_VARARGS };
    char iob_buf[64];
    mdb_iob_t iob;
    mdb_io_t io;
    spbuf_t spb;

    ASSERT(buf != NULL || nbytes == 0);
    iob_spb_create(&iob, iob_buf, sizeof (iob_buf), &io, &spb, buf, nbytes);
    va_copy(ap.val_valist, alist);
    iob_doprnt(&iob, format, &ap);
    mdb_iob_flush(&iob);

    if (spb.spb_bufsiz != 0)
        *spb.spb_buf = '\0';
    else if (buf != NULL && nbytes > 0)
        *--spb.spb_buf = '\0';

    return (spb.spb_total);
}

size_t
mdb_iob_asnprintf(char *buf, size_t nbytes, const char *format,
    const mdb_arg_t *argv)
{
    varglist_t ap = { VAT_ARGVEC };
    char iob_buf[64];
    mdb_iob_t iob;
    mdb_io_t io;
    spbuf_t spb;

    ASSERT(buf != NULL || nbytes == 0);
    iob_spb_create(&iob, iob_buf, sizeof (iob_buf), &io, &spb, buf, nbytes);
    ap.val_argv = argv;
    iob_doprnt(&iob, format, &ap);
    mdb_iob_flush(&iob);

    if (spb.spb_bufsiz != 0)
        *spb.spb_buf = '\0';
    else if (buf != NULL && nbytes > 0)
        *--spb.spb_buf = '\0';

    return (spb.spb_total);
}

/*PRINTFLIKE3*/
size_t
mdb_iob_snprintf(char *buf, size_t nbytes, const char *format, ...)
{
    va_list alist;

    va_start(alist, format);
    nbytes = mdb_iob_vsnprintf(buf, nbytes, format, alist);
    va_end(alist);

    return (nbytes);
}

void
mdb_iob_nputs(mdb_iob_t *iob, const char *s, size_t nbytes)
{
    size_t m, n, nleft = nbytes;
    const char *p, *q = s;

    ASSERT(iob->iob_flags & MDB_IOB_WRONLY);

    if (nbytes == 0)
        return; /* Return immediately if there is no work to do */

    /*
     * If the string contains embedded newlines or tabs, invoke ourself
     * recursively for each string component, followed by a call to the
     * newline or tab routine.  This insures that strings with these
     * characters obey our wrapping and indenting rules, and that strings
     * with embedded newlines are flushed after each newline, allowing
     * the output pager to take over if it is enabled.
     */
    while ((p = strnpbrk(q, "\t\n", nleft)) != NULL) {
        if (p > q)
            mdb_iob_nputs(iob, q, (size_t)(p - q));

        if (*p == '\t')
            mdb_iob_tab(iob);
        else
            mdb_iob_nl(iob);

        nleft -= (size_t)(p - q) + 1;   /* Update byte count */
        q = p + 1;          /* Advance past delimiter */
    }

    /*
     * For a given string component, we determine how many bytes (n) we can
     * copy into our buffer (limited by either cols or bufsiz depending
     * on whether AUTOWRAP is on), copy a chunk into the buffer, and
     * flush the buffer if we reach the end of a line.
     */
    while (nleft != 0) {
        if (iob->iob_flags & MDB_IOB_AUTOWRAP) {
            ASSERT(iob->iob_cols >= iob->iob_nbytes);
            n = iob->iob_cols - iob->iob_nbytes;
        } else {
            ASSERT(iob->iob_bufsiz >= iob->iob_nbytes);
            n = iob->iob_bufsiz - iob->iob_nbytes;
        }

        m = MIN(nleft, n); /* copy at most n bytes in this pass */

        bcopy(q, iob->iob_bufp, m);
        nleft -= m;
        q += m;

        iob->iob_bufp += m;
        iob->iob_nbytes += m;

        if (m == n && nleft != 0) {
            if (iob->iob_flags & MDB_IOB_AUTOWRAP)
                mdb_iob_nl(iob);
            else
                mdb_iob_flush(iob);
        }
    }
}

void
mdb_iob_puts(mdb_iob_t *iob, const char *s)
{
    mdb_iob_nputs(iob, s, strlen(s));
}

void
mdb_iob_putc(mdb_iob_t *iob, int c)
{
    mdb_iob_fill(iob, c, 1);
}

void
mdb_iob_tab(mdb_iob_t *iob)
{
    ASSERT(iob->iob_flags & MDB_IOB_WRONLY);

    if (iob->iob_tabstop != 0) {
        /*
         * Round up to the next multiple of the tabstop.  If this puts
         * us off the end of the line, just insert a newline; otherwise
         * insert sufficient whitespace to reach position n.
         */
        size_t n = (iob->iob_nbytes + iob->iob_tabstop) /
            iob->iob_tabstop * iob->iob_tabstop;

        if (n < iob->iob_cols)
            mdb_iob_fill(iob, ' ', n - iob->iob_nbytes);
        else
            mdb_iob_nl(iob);
    }
}

void
mdb_iob_fill(mdb_iob_t *iob, int c, size_t nfill)
{
    size_t i, m, n;

    ASSERT(iob->iob_flags & MDB_IOB_WRONLY);

    while (nfill != 0) {
        if (iob->iob_flags & MDB_IOB_AUTOWRAP) {
            ASSERT(iob->iob_cols >= iob->iob_nbytes);
            n = iob->iob_cols - iob->iob_nbytes;
        } else {
            ASSERT(iob->iob_bufsiz >= iob->iob_nbytes);
            n = iob->iob_bufsiz - iob->iob_nbytes;
        }

        m = MIN(nfill, n); /* fill at most n bytes in this pass */

        for (i = 0; i < m; i++)
            *iob->iob_bufp++ = (char)c;

        iob->iob_nbytes += m;
        nfill -= m;

        if (m == n && nfill != 0) {
            if (iob->iob_flags & MDB_IOB_AUTOWRAP)
                mdb_iob_nl(iob);
            else
                mdb_iob_flush(iob);
        }
    }
}

void
mdb_iob_ws(mdb_iob_t *iob, size_t n)
{
    if (iob->iob_nbytes + n < iob->iob_cols)
        mdb_iob_fill(iob, ' ', n);
    else
        mdb_iob_nl(iob);
}

void
mdb_iob_nl(mdb_iob_t *iob)
{
    ASSERT(iob->iob_flags & MDB_IOB_WRONLY);

    if (iob->iob_nbytes == iob->iob_bufsiz)
        mdb_iob_flush(iob);

    *iob->iob_bufp++ = '\n';
    iob->iob_nbytes++;

    mdb_iob_flush(iob);
}

ssize_t
mdb_iob_ngets(mdb_iob_t *iob, char *buf, size_t n)
{
    ssize_t resid = n - 1;
    ssize_t len;
    int c;

    if (iob->iob_flags & (MDB_IOB_WRONLY | MDB_IOB_EOF))
        return (EOF); /* can't gets a write buf or a read buf at EOF */

    if (n == 0)
        return (0);   /* we need room for a terminating \0 */

    while (resid != 0) {
        if (iob->iob_nbytes == 0 && iob_read(iob, iob->iob_iop) <= 0)
            goto done; /* failed to refill buffer */

        for (len = MIN(iob->iob_nbytes, resid); len != 0; len--) {
            c = *iob->iob_bufp++;
            iob->iob_nbytes--;

            if (c == EOF || c == '\n')
                goto done;

            *buf++ = (char)c;
            resid--;
        }
    }
done:
    *buf = '\0';
    return (n - resid - 1);
}

int
mdb_iob_getc(mdb_iob_t *iob)
{
    int c;

    if (iob->iob_flags & (MDB_IOB_WRONLY | MDB_IOB_EOF | MDB_IOB_ERR))
        return (EOF); /* can't getc if write-only, EOF, or error bit */

    if (iob->iob_nbytes == 0 && iob_read(iob, iob->iob_iop) <= 0)
        return (EOF); /* failed to refill buffer */

    c = (uchar_t)*iob->iob_bufp++;
    iob->iob_nbytes--;

    return (c);
}

int
mdb_iob_ungetc(mdb_iob_t *iob, int c)
{
    if (iob->iob_flags & (MDB_IOB_WRONLY | MDB_IOB_ERR))
        return (EOF); /* can't ungetc if write-only or error bit set */

    if (c == EOF || iob->iob_nbytes == iob->iob_bufsiz)
        return (EOF); /* can't ungetc EOF, or ungetc if buffer full */

    *--iob->iob_bufp = (char)c;
    iob->iob_nbytes++;
    iob->iob_flags &= ~MDB_IOB_EOF;

    return (c);
}

int
mdb_iob_eof(mdb_iob_t *iob)
{
    return ((iob->iob_flags & (MDB_IOB_RDONLY | MDB_IOB_EOF)) ==
        (MDB_IOB_RDONLY | MDB_IOB_EOF));
}

int
mdb_iob_err(mdb_iob_t *iob)
{
    return ((iob->iob_flags & MDB_IOB_ERR) == MDB_IOB_ERR);
}

ssize_t
mdb_iob_read(mdb_iob_t *iob, void *buf, size_t n)
{
    ssize_t resid = n;
    ssize_t len;

    if (iob->iob_flags & (MDB_IOB_WRONLY | MDB_IOB_EOF | MDB_IOB_ERR))
        return (0); /* can't read if write-only, eof, or error */

    while (resid != 0) {
        if (iob->iob_nbytes == 0 && iob_read(iob, iob->iob_iop) <= 0)
            break; /* failed to refill buffer */

        len = MIN(resid, iob->iob_nbytes);
        bcopy(iob->iob_bufp, buf, len);

        iob->iob_bufp += len;
        iob->iob_nbytes -= len;

        buf = (char *)buf + len;
        resid -= len;
    }

    return (n - resid);
}

/*
 * For now, all binary writes are performed unbuffered.  This has the
 * side effect that the pager will not be triggered by mdb_iob_write.
 */
ssize_t
mdb_iob_write(mdb_iob_t *iob, const void *buf, size_t n)
{
    ssize_t ret;

    if (iob->iob_flags & MDB_IOB_ERR)
        return (set_errno(EIO));
    if (iob->iob_flags & MDB_IOB_RDONLY)
        return (set_errno(EMDB_IORO));

    mdb_iob_flush(iob);
    ret = iob_write(iob, iob->iob_iop, buf, n);

    if (ret < 0 && iob == mdb.m_out)
        longjmp(mdb.m_frame->f_pcb, MDB_ERR_OUTPUT);

    return (ret);
}

int
mdb_iob_ctl(mdb_iob_t *iob, int req, void *arg)
{
    return (IOP_CTL(iob->iob_iop, req, arg));
}

const char *
mdb_iob_name(mdb_iob_t *iob)
{
    if (iob == NULL)
        return ("<NULL>");

    return (IOP_NAME(iob->iob_iop));
}

size_t
mdb_iob_lineno(mdb_iob_t *iob)
{
    return (iob->iob_lineno);
}

size_t
mdb_iob_gettabstop(mdb_iob_t *iob)
{
    return (iob->iob_tabstop);
}

size_t
mdb_iob_getmargin(mdb_iob_t *iob)
{
    return (iob->iob_margin);
}

mdb_io_t *
mdb_io_hold(mdb_io_t *io)
{
    io->io_refcnt++;
    return (io);
}

void
mdb_io_rele(mdb_io_t *io)
{
    ASSERT(io->io_refcnt != 0);

    if (--io->io_refcnt == 0) {
        IOP_CLOSE(io);
        mdb_free(io, sizeof (mdb_io_t));
    }
}

void
mdb_io_destroy(mdb_io_t *io)
{
    ASSERT(io->io_refcnt == 0);
    IOP_CLOSE(io);
    mdb_free(io, sizeof (mdb_io_t));
}

void
mdb_iob_stack_create(mdb_iob_stack_t *stk)
{
    stk->stk_top = NULL;
    stk->stk_size = 0;
}

void
mdb_iob_stack_destroy(mdb_iob_stack_t *stk)
{
    mdb_iob_t *top, *ntop;

    for (top = stk->stk_top; top != NULL; top = ntop) {
        ntop = top->iob_next;
        mdb_iob_destroy(top);
    }
}

void
mdb_iob_stack_push(mdb_iob_stack_t *stk, mdb_iob_t *iob, size_t lineno)
{
    iob->iob_lineno = lineno;
    iob->iob_next = stk->stk_top;
    stk->stk_top = iob;
    stk->stk_size++;
    yylineno = 1;
}

mdb_iob_t *
mdb_iob_stack_pop(mdb_iob_stack_t *stk)
{
    mdb_iob_t *top = stk->stk_top;

    ASSERT(top != NULL);

    stk->stk_top = top->iob_next;
    top->iob_next = NULL;
    stk->stk_size--;

    return (top);
}

size_t
mdb_iob_stack_size(mdb_iob_stack_t *stk)
{
    return (stk->stk_size);
}

/*
 * Stub functions for i/o backend implementors: these stubs either act as
 * pass-through no-ops or return ENOTSUP as appropriate.
 */
ssize_t
no_io_read(mdb_io_t *io, void *buf, size_t nbytes)
{
    if (io->io_next != NULL)
        return (IOP_READ(io->io_next, buf, nbytes));

    return (set_errno(EMDB_IOWO));
}

ssize_t
no_io_write(mdb_io_t *io, const void *buf, size_t nbytes)
{
    if (io->io_next != NULL)
        return (IOP_WRITE(io->io_next, buf, nbytes));

    return (set_errno(EMDB_IORO));
}

off64_t
no_io_seek(mdb_io_t *io, off64_t offset, int whence)
{
    if (io->io_next != NULL)
        return (IOP_SEEK(io->io_next, offset, whence));

    return (set_errno(ENOTSUP));
}

int
no_io_ctl(mdb_io_t *io, int req, void *arg)
{
    if (io->io_next != NULL)
        return (IOP_CTL(io->io_next, req, arg));

    return (set_errno(ENOTSUP));
}

/*ARGSUSED*/
void
no_io_close(mdb_io_t *io)
{
/*
 * Note that we do not propagate IOP_CLOSE down the io stack.  IOP_CLOSE should
 * only be called by mdb_io_rele when an io's reference count has gone to zero.
 */
}

const char *
no_io_name(mdb_io_t *io)
{
    if (io->io_next != NULL)
        return (IOP_NAME(io->io_next));

    return ("(anonymous)");
}

void
no_io_link(mdb_io_t *io, mdb_iob_t *iob)
{
    if (io->io_next != NULL)
        IOP_LINK(io->io_next, iob);
}

void
no_io_unlink(mdb_io_t *io, mdb_iob_t *iob)
{
    if (io->io_next != NULL)
        IOP_UNLINK(io->io_next, iob);
}

int
no_io_setattr(mdb_io_t *io, int req, uint_t attrs)
{
    if (io->io_next != NULL)
        return (IOP_SETATTR(io->io_next, req, attrs));

    return (set_errno(ENOTSUP));
}

void
no_io_suspend(mdb_io_t *io)
{
    if (io->io_next != NULL)
        IOP_SUSPEND(io->io_next);
}

void
no_io_resume(mdb_io_t *io)
{
    if (io->io_next != NULL)
        IOP_RESUME(io->io_next);
}

/*
 * Iterate over the varargs. The first item indicates the mode:
 * MDB_TBL_PRNT
 *  pull out the next vararg as a const char * and pass it and the
 *  remaining varargs to iob_doprnt; if we want to print the column,
 *  direct the output to mdb.m_out otherwise direct it to mdb.m_null
 *
 * MDB_TBL_FUNC
 *  pull out the next vararg as type mdb_table_print_f and the
 *  following one as a void * argument to the function; call the
 *  function with the given argument if we want to print the column
 *
 * The second item indicates the flag; if the flag is set in the flags
 * argument, then the column is printed. A flag value of 0 indicates
 * that the column should always be printed.
 */
void
mdb_table_print(uint_t flags, const char *delimeter, ...)
{
    va_list alist;
    uint_t flg;
    uint_t type;
    const char *fmt;
    mdb_table_print_f *func;
    void *arg;
    mdb_iob_t *out;
    mdb_bool_t first = TRUE;
    mdb_bool_t print;

    va_start(alist, delimeter);

    while ((type = va_arg(alist, uint_t)) != MDB_TBL_DONE) {
        flg = va_arg(alist, uint_t);

        print = flg == 0 || (flg & flags) != 0;

        if (print) {
            if (first)
                first = FALSE;
            else
                mdb_printf("%s", delimeter);
        }

        switch (type) {
        case MDB_TBL_PRNT: {
            varglist_t ap = { VAT_VARARGS };
            fmt = va_arg(alist, const char *);
            out = print ? mdb.m_out : mdb.m_null;
            va_copy(ap.val_valist, alist);
            iob_doprnt(out, fmt, &ap);
            va_end(alist);
            va_copy(alist, ap.val_valist);
            break;
        }

        case MDB_TBL_FUNC:
            func = va_arg(alist, mdb_table_print_f *);
            arg = va_arg(alist, void *);

            if (print)
                func(arg);

            break;

        default:
            warn("bad format type %x\n", type);
            break;
        }
    }

    va_end(alist);
}