Re: [Qemu-devel] [PATCH for-3.0] slirp: Correct size check in m_inc()

[Samuel Thibault <samuel.thibault@gnu.org>]

Dr. David Alan Gilbert, le jeu. 09 août 2018 12:32:05 +0100, a ecrit:
> >    |--datasize---->|---m_len------->
> >    |----------m_size------------------------------>
> >                    |----M_ROOM-------------------->
> >                                     |-M_FREEROOM-->
> > 
> >    ^               ^                               ^
> >    m_dat           m_data                          end of buffer
> > 
> > ("datasize" is a bit misnamed, as it's "size of the leading
> > gap between the start of the buffer and the data"; "gapsize"
> > would be more helpful.)
> > 
> > Anyway, we allocate size + datasize, and
> > m_size == datasize + M_ROOM. We know that size >= M_ROOM,
> > so the allocated buffer must be at least m_size big.
> 
> Ah OK, thanks.
> (That ascii art could do with being in a comment somewhere!)

Indeed. Peter, maybe your Signed-off-by on this? :)

Samuel

commit 4be85a1eeb6b19e91491e689d4d0d054030cbb49
Author: Peter Maydell <peter.maydell@linaro.org>
Date:   Thu Aug 9 23:52:59 2018 +0200

    slirp: document mbuf pointers and sizes
    
    Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

diff --git a/slirp/mbuf.h b/slirp/mbuf.h
index 33b84485d6..a5bb3f9e66 100644
--- a/slirp/mbuf.h
+++ b/slirp/mbuf.h
@@ -47,6 +47,16 @@
  * free the m_ext.  This is inefficient memory-wise, but who cares.
  */
 
+/*
+ *  |--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
  */