Author: glebius
Date: Sat Mar 16 08:55:21 2013
New Revision: 248371
URL: http://svnweb.freebsd.org/changeset/base/248371
Log:
Contrary to what the deleted comment said, the m_move_pkthdr()
will not smash the M_EXT and data pointer, so it is safe to
pass an mbuf with external storage procuded by m_getcl() to
m_move_pkthdr().
Reviewed by: andre
Sponsored by: Nginx, Inc.
Modified:
head/sys/kern/uipc_mbuf.c
Modified: head/sys/kern/uipc_mbuf.c
==============================================================================
--- head/sys/kern/uipc_mbuf.c Sat Mar 16 08:51:47 2013 (r248370)
+++ head/sys/kern/uipc_mbuf.c Sat Mar 16 08:55:21 2013 (r248371)
@@ -1968,43 +1968,18 @@ m_unshare(struct mbuf *m0, int how)
}
/*
- * Allocate new space to hold the copy...
- */
- /* XXX why can M_PKTHDR be set past the first mbuf? */
- if (mprev == NULL && (m->m_flags & M_PKTHDR)) {
- /*
- * NB: if a packet header is present we must
- * allocate the mbuf separately from any cluster
- * because M_MOVE_PKTHDR will smash the data
- * pointer and drop the M_EXT marker.
- */
- MGETHDR(n, how, m->m_type);
- if (n == NULL) {
- m_freem(m0);
- return (NULL);
- }
- M_MOVE_PKTHDR(n, m);
- MCLGET(n, how);
- if ((n->m_flags & M_EXT) == 0) {
- m_free(n);
- m_freem(m0);
- return (NULL);
- }
- } else {
- n = m_getcl(how, m->m_type, m->m_flags);
- if (n == NULL) {
- m_freem(m0);
- return (NULL);
- }
- }
- /*
- * ... and copy the data. We deal with jumbo mbufs
- * (i.e. m_len > MCLBYTES) by splitting them into
- * clusters. We could just malloc a buffer and make
- * it external but too many device drivers don't know
- * how to break up the non-contiguous memory when
+ * Allocate new space to hold the copy and copy the data.
+ * We deal with jumbo mbufs (i.e. m_len > MCLBYTES) by
+ * splitting them into clusters. We could just malloc a
+ * buffer and make it external but too many device drivers
+ * don't know how to break up the non-contiguous memory when
* doing DMA.
*/
+ n = m_getcl(how, m->m_type, m->m_flags);
+ if (n == NULL) {
+ m_freem(m0);
+ return (NULL);
+ }
len = m->m_len;
off = 0;
mfirst = n;
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