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.
This commit is contained in:
parent
80daa4713c
commit
5368b81eb0
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=248371
@ -1968,43 +1968,18 @@ m_unshare(struct mbuf *m0, int how)
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}
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/*
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* Allocate new space to hold the copy...
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*/
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/* XXX why can M_PKTHDR be set past the first mbuf? */
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if (mprev == NULL && (m->m_flags & M_PKTHDR)) {
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/*
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* NB: if a packet header is present we must
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* allocate the mbuf separately from any cluster
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* because M_MOVE_PKTHDR will smash the data
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* pointer and drop the M_EXT marker.
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*/
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MGETHDR(n, how, m->m_type);
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if (n == NULL) {
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m_freem(m0);
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return (NULL);
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}
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M_MOVE_PKTHDR(n, m);
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MCLGET(n, how);
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if ((n->m_flags & M_EXT) == 0) {
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m_free(n);
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m_freem(m0);
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return (NULL);
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}
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} else {
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n = m_getcl(how, m->m_type, m->m_flags);
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if (n == NULL) {
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m_freem(m0);
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return (NULL);
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}
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}
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/*
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* ... and copy the data. We deal with jumbo mbufs
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* (i.e. m_len > MCLBYTES) by splitting them into
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* clusters. We could just malloc a buffer and make
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* it external but too many device drivers don't know
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* how to break up the non-contiguous memory when
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* Allocate new space to hold the copy and copy the data.
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* We deal with jumbo mbufs (i.e. m_len > MCLBYTES) by
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* splitting them into clusters. We could just malloc a
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* buffer and make it external but too many device drivers
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* don't know how to break up the non-contiguous memory when
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* doing DMA.
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*/
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n = m_getcl(how, m->m_type, m->m_flags);
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if (n == NULL) {
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m_freem(m0);
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return (NULL);
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}
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len = m->m_len;
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off = 0;
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mfirst = n;
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