Re: [gentoo-dev] linux-headers and glib-kernel-headers?

[Kumba]

Sven Köhler wrote:

> Hi,
>
> the linux-headers installed the headers from a specific kernel version.
> There seem to be a glibc-kernel-headers package out there. Search the
> LKML for a mail with the subject "glibc-kernel-headers".
>
> I'm still very confused about the linux-headers ebuild. Linux Torvald
> claims that a running system should not update the headers. OK, he only
> recomms not to do that, but the portage offers be an update if i do
> "emerge -upD world". I guess updating the headers could break some
> things - although i cannot imagine which.

Linus is correct in some aspects -- you shouldn't go blindly updating 
headers unless you're willing to risk breakage.

Alot of distributions create headers by symlinking 
/usr/include/{linux,asm} to /usr/src/linux/include/{linux,asm}.  Gentoo 
is one of the distributions that actually installs a separate set of 
headers in /usr/include, leaving you free to do whatever with 
/usr/src/linux (although it helps to keep this as a symlink to the 
source of your running kernel, some programs look for it).

If you do upgrade your headers, all you really need to do is rebuild 
glibc and all should be well.  building glibc against newer headers 
sometimes allows glibc to access new features of the kernel.  The 
SELinux team recently needed to use 2.4.21 headers to access newer 
glibc/kernel features for SELinux because of this.  Rebuilding the 
entire machine also doesn't hurt, but it can be overkill.

The glibc-kernel-headers you speak of are "sanitized" headers mainly 
intended for redhat distributions and are prepared by Arjan van de Ven 
of Redhat.  It was discussed several months ago on whether gentoo should 
use sanitized headers too, but our problem is we support multiple 
architectures, and I do believe the sanitized headers are for i386 only. 
  sparc, mips, ppc, etc.. would all need certain things tweaked in their 
own headers as well for things to work properly.

I think there is some thought on LKML to resolve this finally in 2.6, by 
creating a split in the kernel headers, separating out a sanitized set 
of user-space headers and headers intended exclusively for the kernel. 
No idea when this idea might be implemented in 2.6....it might become a 
2.7 feature.


--Kumba

-- 
"Such is oft the course of deeds that move the wheels of the world: 
small hands do them because they must, while the eyes of the great are 
elsewhere."  --Elrond


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