fix m_adj to work right trimming from tail (there can be 0-length mbufs

in the chain); make m_pullup use first mbuf if enough room without copying,
and pullup a bit extra for next-level protocol

SCCS-vsn: sys/kern/uipc_mbuf.c 6.8

diff --git a/usr/src/sys/kern/uipc_mbuf.c b/usr/src/sys/kern/uipc_mbuf.c
index 1c4331d..911f3bc 100644 (file)
--- a/usr/src/sys/kern/uipc_mbuf.c
+++ b/usr/src/sys/kern/uipc_mbuf.c
@@ -3,7 +3,7 @@
  * All rights reserved.  The Berkeley software License Agreement
  * specifies the terms and conditions for redistribution.
  *
  * All rights reserved.  The Berkeley software License Agreement
  * specifies the terms and conditions for redistribution.
  *

- *     @(#)uipc_mbuf.c 6.7 (Berkeley) %G%
+ *     @(#)uipc_mbuf.c 6.8 (Berkeley) %G%

  */
 
 #include "../machine/pte.h"
  */
 
 #include "../machine/pte.h"


@@ -277,7 +277,8 @@ m_adj(mp, len)
        struct mbuf *mp;
        register int len;
 {
        struct mbuf *mp;
        register int len;
 {

-       register struct mbuf *m, *n;
+       register struct mbuf *m;
+       register count;

 
        if ((m = mp) == NULL)
                return;
 
        if ((m = mp) == NULL)
                return;


@@ -294,49 +295,75 @@ m_adj(mp, len)
                        }
                }
        } else {
                        }
                }
        } else {

-               /* a 2 pass algorithm might be better */
+               /*
+                * Trim from tail.  Scan the mbuf chain,
+                * calculating its length and finding the last mbuf.
+                * If the adjustment only affects this mbuf, then just
+                * adjust and return.  Otherwise, rescan and truncate
+                * after the remaining size.
+                */

                len = -len;
                len = -len;

-               while (len > 0 && m->m_len != 0) {
-                       while (m != NULL && m->m_len != 0) {
-                               n = m;
-                               m = m->m_next;
-                       }
-                       if (n->m_len <= len) {
-                               len -= n->m_len;
-                               n->m_len = 0;
-                               m = mp;
-                       } else {
-                               n->m_len -= len;
+               count = 0;
+               for (;;) {
+                       count += m->m_len;
+                       if (m->m_next == (struct mbuf *)0)
+                               break;
+                       m = m->m_next;
+               }
+               if (m->m_len >= len) {
+                       m->m_len -= len;
+                       return;
+               }
+               count -= len;
+               /*
+                * Correct length for chain is "count".
+                * Find the mbuf with last data, adjust its length,
+                * and toss data from remaining mbufs on chain.
+                */
+               for (m = mp; m; m = m->m_next) {
+                       if (m->m_len >= count) {
+                               m->m_len = count;

                                break;
                        }
                                break;
                        }

+                       count -= m->m_len;

                }
                }

+               while (m = m->m_next)
+                       m->m_len = 0;

        }
 }
 
 /*
  * Rearange an mbuf chain so that len bytes are contiguous
  * and in the data area of an mbuf (so that mtod and dtom
        }
 }
 
 /*
  * Rearange an mbuf chain so that len bytes are contiguous
  * and in the data area of an mbuf (so that mtod and dtom

- * will work for a structure of size len).
- * Returns the resulting mbuf chain on success,
- * frees it and returns null on failure.
+ * will work for a structure of size len).  Returns the resulting
+ * mbuf chain on success, frees it and returns null on failure.
+ * If there is room, it will add up to MPULL_EXTRA bytes to the
+ * contiguous region in an attempt to avoid being called next time.

  */
 struct mbuf *
  */
 struct mbuf *

-m_pullup(m0, len)
-       struct mbuf *m0;
+m_pullup(n, len)
+       register struct mbuf *n;

        int len;
 {
        int len;
 {

-       register struct mbuf *m, *n;
-       int count;
+       register struct mbuf *m;
+       register int count;
+       int space;

 
 

-       n = m0;
-       if (len > MLEN)
-               goto bad;
-       MGET(m, M_DONTWAIT, n->m_type);
-       if (m == 0)
-               goto bad;
-       m->m_len = 0;
+       if (n->m_off + len <= MMAXOFF && n->m_next) {
+               m = n;
+               n = n->m_next;
+               len -= m->m_len;
+       } else {
+               if (len > MLEN)
+                       goto bad;
+               MGET(m, M_DONTWAIT, n->m_type);
+               if (m == 0)
+                       goto bad;
+               m->m_len = 0;
+       }
+       space = MMAXOFF - m->m_off;

        do {
        do {

-               count = MIN(n->m_len, len);
+               count = MIN(MIN(space - m->m_len, len + MPULL_EXTRA), n->m_len);

                bcopy(mtod(n, caddr_t), mtod(m, caddr_t)+m->m_len,
                  (unsigned)count);
                len -= count;
                bcopy(mtod(n, caddr_t), mtod(m, caddr_t)+m->m_len,
                  (unsigned)count);
                len -= count;


@@ -346,8 +373,8 @@ m_pullup(m0, len)
                        n->m_off += count;
                else
                        n = m_free(n);
                        n->m_off += count;
                else
                        n = m_free(n);

-       } while (len && n);
-       if (len) {
+       } while (len > 0 && n);
+       if (len > 0) {

                (void) m_free(m);
                goto bad;
        }
                (void) m_free(m);
                goto bad;
        }