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[lwip-users] [lwip] Bug in pbuf_dechain()
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From: |
Lieverse, Paul |
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Subject: |
[lwip-users] [lwip] Bug in pbuf_dechain() |
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Date: |
Wed, 08 Jan 2003 22:39:33 -0000 |
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Hi,
I detected an error in pbuf_dechain. This function is currently not used,
but if it's there, it should be correct.
The problem is that the tot_len field of the tail is not adjusted.
Walking through a simple example already shows this.
For example:
pbuf_chain(a, b);
pbuf_chain(a, c);
d = pbuf_dechain(a);
The tot_len of d (pointing to b) is now incorrect).
The new code: (the if statement plus body is added)
/* pbuf_dechain():
*
* Adjusts the ->tot_len field of the pbuf and of the tail (if any) of the
pbuf
* chain and returns the tail.
*/
/*--------------------------------------------------------------------------
---------*/
struct pbuf *
pbuf_dechain(struct pbuf *p)
{
struct pbuf *q;
q = p->next;
if (q != NULL) {
q->tot_len = p->tot_len - p->len;
}
p->tot_len = p->len;
p->next = NULL;
return q;
}
/*--------------------------------------------------------------------------
---------*/
Paul
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<META NAME=3D"Generator" CONTENT=3D"MS Exchange Server version =
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<TITLE>Bug in pbuf_dechain()</TITLE>
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<BODY>
<P><FONT SIZE=3D2 FACE=3D"Arial">Hi,</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">I detected an error in pbuf_dechain. =
This function is currently not used, </FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">but if it's there, it should be =
correct.</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">The problem is that the tot_len field =
of the tail is not adjusted. </FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">Walking through a simple example =
already shows this.</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">For example:</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial"> pbuf_chain(a, b); =
</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial"> pbuf_chain(a, c); =
</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial"> d =3D =
pbuf_dechain(a); </FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">The tot_len of d (pointing to b) is =
now incorrect).</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">The new code: (the if statement plus =
body is added)</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Courier New">/* pbuf_dechain():</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> *</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> * Adjusts the =
->tot_len field of the pbuf</FONT> <FONT SIZE=3D2 FACE=3D"Courier =
New">and of the tail (if any) of the pbuf</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> * chain and returns the =
tail.</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> */</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier =
New">/*-----------------------------------------------------------------=
------------------*/</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New">struct pbuf *</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New">pbuf_dechain(struct pbuf =
*p)</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New">{</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> struct pbuf *q;</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> </FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> q =3D p->next;</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> if (q !=3D NULL) =
{</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> =
q->tot_len =3D p->tot_len - p->len;</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> }</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> p->tot_len =3D =
p->len;</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> p->next =3D =
NULL;</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New"> return q;</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier New">}</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Courier =
New">/*-----------------------------------------------------------------=
------------------*/</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Courier New">Paul</FONT>
</P>
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