Subject: Re: compile breakage due to [SK_BUFF]: Convert skb->end to sk_buff_data_t

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Sun, 13 May 2007 20:27:35 -0300

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 <[email-masked]>
>> AuthorDate: Thu Apr 19 20:43:29 2007 -0700
>> Committer:  David S. Miller <[email-masked]>
>> 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 <[email-masked]>
>>     Signed-off-by: David S. Miller <[email-masked]>
>>     
>
> 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@rhun:~/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?

- Arnaldo