if_tap unaligned access problem

[Maksim Yevmenkin]

John-Mark Gurney wrote:
> Maksim Yevmenkin wrote this message on Mon, May 02, 2005 at 09:38 -0700:
> 
>>>>>>>>i think we have few options here:
>>>>>>>>
>>>>>>>>1) revert back original tapwrite function that was changed in v. 
>>>>>>>>1.48 and set offset to 2 bytes in top mbuf
>>>>>>>>
>>>>>>>>2) change current version of tapwrite so it would m_prepend and 
>>>>>>>>m_pullup mbuf after m_uiotombuf
>>>>>>>>
>>>>>>>>3) change m_uiotombuf to accept one more parameter - mbuf offset at 
>>>>>>>>which data should be copied. there are not that many users of 
>>>>>>>>m_uiotombuf
>>>>
>>>>please find and review the attached patch (untested) that implements 
>>>>option (3) above.
>>
>>any objections to the attached (revised) patch? can i commit it?
>>
>>thanks,
>>max
> 
> 
>>Index: sys/kern/uipc_mbuf.c
>>===================================================================
>>RCS file: /home/ncvs/src/sys/kern/uipc_mbuf.c,v
>>retrieving revision 1.147
>>diff -u -r1.147 uipc_mbuf.c
>>--- sys/kern/uipc_mbuf.c	17 Mar 2005 19:34:57 -0000	1.147
>>+++ sys/kern/uipc_mbuf.c	2 May 2005 16:33:41 -0000
>>@@ -1333,7 +1333,7 @@
>> #endif
>> 
>> struct mbuf *
>>-m_uiotombuf(struct uio *uio, int how, int len)
>>+m_uiotombuf(struct uio *uio, int how, int len, int align)
>> {
>> 	struct mbuf *m_new = NULL, *m_final = NULL;
>> 	int progress = 0, error = 0, length, total;
>>@@ -1342,12 +1342,15 @@
>> 		total = min(uio->uio_resid, len);
>> 	else
>> 		total = uio->uio_resid;
>>-	if (total > MHLEN)
>>+	if (align >= MHLEN)
>>+		goto nospace;
>>+	if (total + align > MHLEN)
> 
> 
> I kinda noticed this a bit ago, but didn't think much of it till now...
> do we want to allow align >= MHLEN if total requires a cluster?  since
> if we use a cluster, we'd have enough space for a larger align...
> 

well, you got me here :) MHLEN is 200+ bytes, so i can not imagine why 
one would want to align something on 200+ bytes. i was kind of hoping 
that no one would ever need to align on anything greater then 128 bytes. 
perhaps i'm wrong here?

thanks,
max