netdev - Re: compile breakage due to [SK_BUFF]: Convert skb->end to sk_buff_data

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Message-Id: <20070513172732.2fc8c65c.randy.dunlap@oracle.com>
Date:	Sun, 13 May 2007 17:27:32 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Muli Ben-Yehuda <muli@...ibm.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: compile breakage due to [SK_BUFF]: Convert skb->end to
 sk_buff_data_t

On Sun, 13 May 2007 20:27:35 -0300 Arnaldo Carvalho de Melo wrote:

> Muli Ben-Yehuda wrote:
> > On Fri, Apr 27, 2007 at 05:03:44PM +0000, Linux Kernel Mailing List wrote:
> >
> >   
> >> Gitweb:     http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=4305b541357ddbd205aa145dc378926b7cb12283
> >> Commit:     4305b541357ddbd205aa145dc378926b7cb12283
> >> Parent:     27a884dc3cb63b93c2b3b643f5b31eed5f8a4d26
> >> Author:     Arnaldo Carvalho de Melo <acme@...hat.com>
> >> AuthorDate: Thu Apr 19 20:43:29 2007 -0700
> >> Committer:  David S. Miller <davem@...set.davemloft.net>
> >> CommitDate: Wed Apr 25 22:26:29 2007 -0700
> >>
> >>     [SK_BUFF]: Convert skb->end to sk_buff_data_t
> >>     
> >>     Now to convert the last one, skb->data, that will allow many simplifications
> >>     and removal of some of the offset helpers.
> >>     
> >>     Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> >>     Signed-off-by: David S. Miller <davem@...emloft.net>
> >>     
> >
> > This patch and the previous one breaks the compilation on one of my
> > machines. Specifically, this bit:
> >
> >   
> >> @@ -632,12 +644,13 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
> >>  	/* Copy only real data... and, alas, header. This should be
> >>  	 * optimized for the cases when header is void. */
> >>  	memcpy(data + nhead, skb->head,
> >> -		skb->tail
> >> -#ifndef NET_SKBUFF_DATA_USES_OFFSET
> >> -		- skb->head
> >> +#ifdef NET_SKBUFF_DATA_USES_OFFSET
> >> +		skb->tail);
> >> +#else
> >> +		skb->tail - skb->head);
> >>  #endif
> >> -		);
> >> -	memcpy(data + size, skb->end, sizeof(struct skb_shared_info));
> >> +	memcpy(data + size, skb_end_pointer(skb),
> >> +	       sizeof(struct skb_shared_info));
> >>  
> >>  	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
> >>  		get_page(skb_shinfo(skb)->frags[i].page);
> >>     
> >
> > Causes this compile error:
> >
> > /home/muli/kernel/trident/trident.git/net/core/skbuff.c:648:1: directives may not be used inside a macro argument
> > /home/muli/kernel/trident/trident.git/net/core/skbuff.c:647:39: unterminated argument list invoking macro "memcpy"
> > /home/muli/kernel/trident/trident.git/net/core/skbuff.c: In function `pskb_expand_head':
> > /home/muli/kernel/trident/trident.git/net/core/skbuff.c:651: `memcpy' undeclared (first use in this function)
> > /home/muli/kernel/trident/trident.git/net/core/skbuff.c:651: (Each undeclared identifier is reported only once
> > /home/muli/kernel/trident/trident.git/net/core/skbuff.c:651: for each function it appears in.)
> > /home/muli/kernel/trident/trident.git/net/core/skbuff.c:651: syntax error before "skb"
> >
> > muli@...n:~/kernel/trident/trident.git$ gcc -v
> > Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2.3/specs
> > Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux
> > Thread model: posix
> > gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-53)
> >
> > It happens because memcpy ends up being a macro, and this gcc dislikes
> > having a preprocessor directive inside a macro argument. I don't know
> > if if it's valid in general, but Documentation/Changes does say we
> > still support gcc 3.2...
> >   
> 
> Well, the fix is easy, can you provide a patch?

btw, sparse dislikes that ifdeffery also.

---
~Randy
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