[PATCH] IPv6 can't be built as module additionally

[PATCH] IPv6 can't be built as module additionally

[Jirka Kosina]

Hi,

It is not possible to build ipv6 for already compiled and running kernel, 
recompilation of whole kernel, even if building as a module, is typically 
a must. This is because ipv6-specific functions in drivers/char/random.c 
are inside #ifdefs, and as random.c is almost always built directly into 
kernel, recompilation of whole kernel can't be avoided. The corresponding 
functions for IPv4 in random.c are not inside those ifdefs, and I think 
that IPv6 shouldn't be either. Recompiling whole kernel just because I 
want to build ipv6 module is quite annoying. The following patch removes 
those ifdefs and makes additional compilation of ipv6 module possible.

--- drivers/char/random.c.old	Mon May 10 04:32:00 2004
+++ drivers/char/random.c	Thu May 20 23:58:27 2004
@@ -2146,8 +2146,6 @@
 	/* Alternative: return sum of all words? */
 }
 
-#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
-
 static __u32 twothirdsMD4Transform (__u32 const buf[4], __u32 const in[12])
 {
 	__u32	a = buf[0], b = buf[1], c = buf[2], d = buf[3];
@@ -2197,7 +2195,6 @@
 	return buf[1] + b;	/* "most hashed" word */
 	/* Alternative: return sum of all words? */
 }
-#endif
 
 #undef ROUND
 #undef F
@@ -2271,7 +2268,6 @@
 	return keyptr;
 }
 
-#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 __u32 secure_tcpv6_sequence_number(__u32 *saddr, __u32 *daddr,
 				   __u16 sport, __u16 dport)
 {
@@ -2309,7 +2305,6 @@
 }
 
 EXPORT_SYMBOL(secure_ipv6_id);
-#endif
 
 
 __u32 secure_tcp_sequence_number(__u32 saddr, __u32 daddr,

-- 
JiKos.

Re: [PATCH] IPv6 can't be built as module additionally

[David S. Miller]

On Fri, 21 May 2004 00:16:06 +0200 (CEST)
Jirka Kosina <jikos@jikos.cz> wrote:

> This is because ipv6-specific functions in drivers/char/random.c 
> are inside #ifdefs, and as random.c is almost always built directly into 
> kernel, recompilation of whole kernel can't be avoided.

This is the smallest problem, several main kernel data structures
change size based upon whether ipv6 has been enabled in any way
or not.

So even with your patch, compiling ipv6 outside of the kernel will
still not work even though it might build.

This has been discussed to death in the past I do believe :-)

Re: [PATCH] IPv6 can't be built as module additionally

[Andy Isaacson]

On Thu, May 20, 2004 at 03:50:42PM -0700, David S. Miller wrote:
> On Fri, 21 May 2004 00:16:06 +0200 (CEST)
> Jirka Kosina <jikos@jikos.cz> wrote:
> > This is because ipv6-specific functions in drivers/char/random.c 
> > are inside #ifdefs, and as random.c is almost always built directly into 
> > kernel, recompilation of whole kernel can't be avoided.
> 
> This is the smallest problem, several main kernel data structures
> change size based upon whether ipv6 has been enabled in any way
> or not.
> 
> So even with your patch, compiling ipv6 outside of the kernel will
> still not work even though it might build.

Dave, would you be opposed to making IPv6 the default, with IPv4-only a
selectable option under CONFIG_EMBEDDED or whatever umbrella "I know
what I'm doing, let me remove vital parts of the kernel" config option
is considered appropriate?

It seems that the cost of IPv6 is small enough in most scenarios that
virtually everyone should be enabling it, and those who turn it off
should be willing to turn on CONFIG_EMBEDDED or whatever the umbrella
option is called.  I note with dismay that of the 18 arch/*/defconfig
files I perused, 13 do not set CONFIG_IPV6, 3 have =m, and 2 have =y.

-andy

Re: [PATCH] IPv6 can't be built as module additionally

[David S. Miller]

On Thu, 20 May 2004 18:30:13 -0500
Andy Isaacson <adi@hexapodia.org> wrote:

> Dave, would you be opposed to making IPv6 the default, with IPv4-only a
> selectable option under CONFIG_EMBEDDED or whatever umbrella "I know
> what I'm doing, let me remove vital parts of the kernel" config option
> is considered appropriate?

Not really, this has been discussed to death before.

Re: [PATCH] IPv6 can't be built as module additionally

[Valdis.Kletnieks]

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On Fri, 21 May 2004 00:16:06 +0200, Jirka Kosina said:

> It is not possible to build ipv6 for already compiled and running kernel, 
> recompilation of whole kernel, even if building as a module, is typically 
> a must. This is because ipv6-specific functions in drivers/char/random.c 
> are inside #ifdefs, and as random.c is almost always built directly into 
> kernel, recompilation of whole kernel can't be avoided.

What you're getting bit by is the fact that some heavily-used kernel structures
get their size changed when you define CONFIG_IPV6, and *that* forces
the rebuild.

Rebuilding random.o should be relatively fast - that's 1 CC, then a few LD's
to rebuild drivers/char/built-in.o, then drivers/build-in.o, then increment the
kernel build version, and rebuild vmlinux.  Shouldn't be more than 30-40 lines of
output, total.  

In addition, the proposed removal of the ifdef's causes bloat in random.c for
those systems that don't configure it.  So it's a bad fix for the wrong problem...

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