12364 mdb trips assertion related to autowrap

*** 22,32 ****
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
  /*
!  * Copyright (c) 2019, 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.
--- 22,32 ----
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
  /*
!  * Copyright 2020 Joyent, Inc.
   * Copyright (c) 2016 by Delphix. All rights reserved.
   */
  
  /*
   * MDB uses its own enhanced standard i/o mechanism for all input and output.
*** 1775,1784 ****
--- 1775,1805 ----
          va_end(alist);
  
          return (nbytes);
  }
  
+ /*
+  * Return how many bytes we can copy into our buffer, limited by either cols or
+  * bufsiz depending on whether AUTOWRAP is on.  Note that typically,
+  * mdb_iob_set_autowrap() will have already checked for an existing
+  * "->iob_nbytes > ->iob_cols" situation, but we double check here anyway.
+  */
+ static size_t
+ iob_bufleft(mdb_iob_t *iob)
+ {
+         if (IOB_AUTOWRAP(iob)) {
+                 if (iob->iob_cols < iob->iob_nbytes) {
+                         mdb_iob_nl(iob);
+                         ASSERT(iob->iob_cols >= iob->iob_nbytes);
+                 }
+                 return (iob->iob_cols - iob->iob_nbytes);
+         }
+ 
+         ASSERT(iob->iob_bufsiz >= iob->iob_nbytes);
+         return (iob->iob_bufsiz - iob->iob_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;
*** 1808,1831 ****
                  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_AUTOWRAP(iob)) {
!                         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;
--- 1829,1843 ----
                  nleft -= (size_t)(p - q) + 1;   /* Update byte count */
                  q = p + 1;                      /* Advance past delimiter */
          }
  
          /*
!          * For a given string component, we copy a chunk into the buffer, and
           * flush the buffer if we reach the end of a line.
           */
          while (nleft != 0) {
!                 n = iob_bufleft(iob);
                  m = MIN(nleft, n); /* copy at most n bytes in this pass */
  
                  bcopy(q, iob->iob_bufp, m);
                  nleft -= m;
                  q += m;
*** 1882,1899 ****
          size_t i, m, n;
  
          ASSERT(iob->iob_flags & MDB_IOB_WRONLY);
  
          while (nfill != 0) {
!                 if (IOB_AUTOWRAP(iob)) {
!                         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;
  
--- 1894,1904 ----
          size_t i, m, n;
  
          ASSERT(iob->iob_flags & MDB_IOB_WRONLY);
  
          while (nfill != 0) {
!                 n = iob_bufleft(iob);
                  m = MIN(nfill, n); /* fill at most n bytes in this pass */
  
                  for (i = 0; i < m; i++)
                          *iob->iob_bufp++ = (char)c;
  
*** 2166,2175 ****
--- 2171,2200 ----
  mdb_iob_stack_size(mdb_iob_stack_t *stk)
  {
          return (stk->stk_size);
  }
  
+ /*
+  * This only enables autowrap for iobs that are already autowrap themselves such
+  * as mdb.m_out typically.
+  *
+  * Note that we might be the middle of the iob buffer at this point, and
+  * specifically, iob->iob_nbytes could be more than iob->iob_cols.  As that's
+  * not a valid situation, we may need to do an autowrap *now*.
+  *
+  * In theory, we would need to do this across all MDB_IOB_AUTOWRAP iob's;
+  * instead, we have a failsafe in iob_bufleft().
+  */
+ void
+ mdb_iob_set_autowrap(mdb_iob_t *iob)
+ {
+         mdb.m_flags |= MDB_FL_AUTOWRAP;
+         if (IOB_WRAPNOW(iob, 0))
+                 mdb_iob_nl(iob);
+         ASSERT(iob->iob_cols >= iob->iob_nbytes);
+ }
+ 
  /*
   * Stub functions for i/o backend implementors: these stubs either act as
   * pass-through no-ops or return ENOTSUP as appropriate.
   */
  ssize_t