Date: Fri, 3 Feb 2012 06:34:57 +0900 From: rozhuk.im@gmail.com To: "'Navdeep Parhar'" <nparhar@gmail.com> Cc: freebsd-net@freebsd.org Subject: RE: m_pullup - fail Message-ID: <4f2b0188.82b7cc0a.2dad.ffff88e9@mx.google.com> In-Reply-To: <CAPFoGT_6Qp-_qtQ4bDM6VMwG8D4P6m5JYjy5zoUXAZ1aFQBTdQ@mail.gmail.com> References: <4f298d95.82b7cc0a.49b2.5d24@mx.google.com> <CAPFoGT_6Qp-_qtQ4bDM6VMwG8D4P6m5JYjy5zoUXAZ1aFQBTdQ@mail.gmail.com>
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The function does not allow access to data if m_flags & M_EXT size and more
MHLEN, although the data is actually available.
Why if there is no m_flags & M_PKTHDR size anyway MHLEN instead MLEN?
As an improvement, you can try to copy the data from the current m in
m_next, if m is not enough space and enough m_next (case m_flags & M_EXT).
If I figured out MBUF then m_pullup should take maximum length according to
this macro
#define M_PULLUP_MAX(m) \
((m)->m_flags & M_EXT ? \
(M_WRITABLE(m) ? (m)->m_ext.ext_size : 0) : \
(m)->m_flags & M_PKTHDR ? MHLEN : MLEN )
/usr/src/sys/sys/param.h:#define MSIZE 256 /* size of
an mbuf */
/usr/src/sys/sys/mbuf.h:#define MLEN (MSIZE - sizeof(struct
m_hdr)) /* normal data len */
/usr/src/sys/sys/mbuf.h:#define MHLEN (MLEN - sizeof(struct
pkthdr)) /* data len w/pkthdr */
#define M_EXT 0x00000001 /* has associated external storage */
/*
* If first mbuf has no cluster, and has room for len bytes
* without shifting current data, pullup into it,
* otherwise allocate a new mbuf to prepend to the chain.
*/
if ((n->m_flags & M_EXT) == 0 &&
n->m_data + len < &n->m_dat[MLEN] && n->m_next) {
if (n->m_len >= len)
return (n);
m = n;
n = n->m_next;
len -= m->m_len;
} else {
if (len > MHLEN)
goto bad;
MGET(m, M_DONTWAIT, n->m_type);
if (m == NULL)
goto bad;
m->m_len = 0;
if (n->m_flags & M_PKTHDR)
M_MOVE_PKTHDR(m, n);
}
> -----Original Message-----
> From: Navdeep Parhar [mailto:nparhar@gmail.com]
> Sent: Thursday, February 02, 2012 3:54 PM
> To: Rozhuk.IM@gmail.com
> Cc: freebsd-net@freebsd.org
> Subject: Re: m_pullup - fail
>
> On Wed, Feb 1, 2012 at 11:07 AM, <rozhuk.im@gmail.com> wrote:
> > Hello!
> >
> >
> > The function always returns an error and remove the chain MBUF for
> two
> > or more generated on the same host.
> > If the pre-call m_defrag no error occurs.
> > This is normal behavior?
> > How to know in advance the maximum size for MBUF that does not cause
> a
> > failure in m_pullup?
>
> You can't pullup more than MHLEN bytes into a pkthdr mbuf if it's not
> associated with an external cluster. See the last sentence in this
> excerpt from mbuf(9):
>
> m_pullup(mbuf, len)
> Arrange that the first len bytes of an mbuf chain are
> contiguous
> and lay in the data area of mbuf, so they are accessible
> with
> mtod(mbuf, type). It is important to remember that this may
> involve reallocating some mbufs and moving data so all
> pointers
> referencing data within the old mbuf chain must be
> recalculated or
> made invalid. Return the new mbuf chain on success, NULL on
> fail-
> ure (the mbuf chain is freed in this case). Note: It does
> not
> allocate any mbuf clusters, so len must be less than MHLEN.
>
> Regards,
> Navdeep
> >
> >
> > mbuf: 0xfffffe0074fc0600 len: 42, next: 0xfffffe0073a45800, 2<pkthdr>
> > mbuf: 0xfffffe0073a45800 len: 210, next: 0, 1<ext>
> > FAIL: m_pullup: m_pkthdr.len = 252, m_len = 42, pullup_len = 252
> >
> >
> >
> > _______________________________________________
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