The functions m_copym() and m_copypacket() return read-only copies,
because in the case of mbuf clusters they only increment the reference count rather than actually copying the data. Add comments to this effect, and add a new routine called m_dup() that returns a real, writable copy of an mbuf chain. This is preliminary work required for implementing 'ipfw tee'. Reviewed by: julian
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parent
63e2ac54d1
commit
1c38f2ea70
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=54002
@ -423,6 +423,8 @@ m_prepend(m, len, how)
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* Make a copy of an mbuf chain starting "off0" bytes from the beginning,
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* continuing for "len" bytes. If len is M_COPYALL, copy to end of mbuf.
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* The wait parameter is a choice of M_WAIT/M_DONTWAIT from caller.
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* Note that the copy is read-only, because clusters are not copied,
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* only their reference counts are incremented.
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*/
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#define MCFail (mbstat.m_mcfail)
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@ -499,6 +501,8 @@ m_copym(m, off0, len, wait)
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/*
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* Copy an entire packet, including header (which must be present).
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* An optimization of the common case `m_copym(m, 0, M_COPYALL, how)'.
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* Note that the copy is read-only, because clusters are not copied,
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* only their reference counts are incremented.
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*/
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struct mbuf *
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m_copypacket(m, how)
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@ -592,6 +596,80 @@ m_copydata(m, off, len, cp)
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}
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}
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/*
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* Copy a packet header mbuf chain into a completely new chain, including
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* copying any mbuf clusters. Use this instead of m_copypacket() when
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* you need a writable copy of an mbuf chain.
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*/
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struct mbuf *
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m_dup(m, how)
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struct mbuf *m;
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int how;
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{
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struct mbuf **p, *top = NULL;
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int remain, moff, nsize;
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/* Sanity check */
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if (m == NULL)
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return (0);
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KASSERT((m->m_flags & M_PKTHDR) != 0, ("%s: !PKTHDR", __FUNCTION__));
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/* While there's more data, get a new mbuf, tack it on, and fill it */
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remain = m->m_pkthdr.len;
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moff = 0;
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p = ⊤
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while (remain > 0 || top == NULL) { /* allow m->m_pkthdr.len == 0 */
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struct mbuf *n;
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/* Get the next new mbuf */
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MGET(n, how, m->m_type);
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if (n == NULL)
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goto nospace;
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if (top == NULL) { /* first one, must be PKTHDR */
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M_COPY_PKTHDR(n, m);
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nsize = MHLEN;
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} else /* not the first one */
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nsize = MLEN;
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if (remain >= MINCLSIZE) {
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MCLGET(n, how);
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if ((n->m_flags & M_EXT) == 0) {
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(void)m_free(n);
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goto nospace;
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}
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nsize = MCLBYTES;
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}
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n->m_len = 0;
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/* Link it into the new chain */
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*p = n;
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p = &n->m_next;
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/* Copy data from original mbuf(s) into new mbuf */
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while (n->m_len < nsize && m != NULL) {
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int chunk = min(nsize - n->m_len, m->m_len - moff);
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bcopy(m->m_data + moff, n->m_data + n->m_len, chunk);
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moff += chunk;
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n->m_len += chunk;
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remain -= chunk;
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if (moff == m->m_len) {
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m = m->m_next;
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moff = 0;
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}
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}
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/* Check correct total mbuf length */
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KASSERT((remain > 0 && m != NULL) || (remain == 0 && m == NULL),
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("%s: bogus m_pkthdr.len", __FUNCTION__));
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}
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return (top);
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nospace:
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m_freem(top);
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MCFail++;
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return (0);
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}
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/*
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* Concatenate mbuf chain n to m.
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* Both chains must be of the same type (e.g. MT_DATA).
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@ -417,6 +417,7 @@ struct mbuf *m_copym __P((struct mbuf *, int, int, int));
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struct mbuf *m_copypacket __P((struct mbuf *, int));
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struct mbuf *m_devget __P((char *, int, int, struct ifnet *,
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void (*copy)(char *, caddr_t, u_int)));
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struct mbuf *m_dup __P((struct mbuf *, int));
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struct mbuf *m_free __P((struct mbuf *));
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struct mbuf *m_get __P((int, int));
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struct mbuf *m_getclr __P((int, int));
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