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slirp: document mbuf pointers and sizes

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and fix confusing datasize name into gapsize in m_inc.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
This commit is contained in:
Peter Maydell 2018-08-09 23:52:59 +02:00 committed by Samuel Thibault
parent 3c2d304284
commit 632dd719b3
2 changed files with 20 additions and 7 deletions
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14
slirp/mbuf.c
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@ -151,7 +151,7 @@ m_cat(struct mbuf *m, struct mbuf *n)
void
m_inc(struct mbuf *m, int size)
{
int datasize;
int gapsize;
/* some compilers throw up on gotos. This one we can fake. */
if (M_ROOM(m) > size) {
@ -159,17 +159,17 @@ m_inc(struct mbuf *m, int size)
}
if (m->m_flags & M_EXT) {
datasize = m->m_data - m->m_ext;
m->m_ext = g_realloc(m->m_ext, size + datasize);
gapsize = m->m_data - m->m_ext;
m->m_ext = g_realloc(m->m_ext, size + gapsize);
} else {
datasize = m->m_data - m->m_dat;
m->m_ext = g_malloc(size + datasize);
gapsize = m->m_data - m->m_dat;
m->m_ext = g_malloc(size + gapsize);
memcpy(m->m_ext, m->m_dat, m->m_size);
m->m_flags |= M_EXT;
}
m->m_data = m->m_ext + datasize;
m->m_size = size + datasize;
m->m_data = m->m_ext + gapsize;
m->m_size = size + gapsize;
}

13
slirp/mbuf.h
View File

@ -47,6 +47,19 @@
* free the m_ext. This is inefficient memory-wise, but who cares.
*/
/*
* mbufs allow to have a gap between the start of the allocated buffer (m_ext if
* M_EXT is set, m_dat otherwise) and the in-use data:
*
* |--gapsize----->|---m_len------->
* |----------m_size------------------------------>
* |----M_ROOM-------------------->
* |-M_FREEROOM-->
*
* ^ ^ ^
* m_dat/m_ext m_data end of buffer
*/
/*
* How much room is in the mbuf, from m_data to the end of the mbuf
*/