Re: [gentoo-server] linux-headers: insanity? WAS: linux-headers update?

[Wes Kurdziolek]

My point entirely.  I just used fewer words and left out the
nitty-gritty.  Thanks for covering the details, though.

On Thu, 2005-03-31 at 16:02 +0100, Kerin Millar wrote:
> Wes Kurdziolek wrote:
> > Linus meant that the kernel headers shouldn't be a moving target --
> > changing the kernel headers w/o accounting for all the packages that
> > rely on them is dangerous.  It has the potential to break glibc which
> > virtually everything in a Linux system depends on.
>
> Sorry but that's not simply not correct. Changing the headers does
> absolutely *nothing* unless you (re)build a package that includes a
> portion of those headers. After all, they are simply headers - it's not
> a library. The issue arises if you build said package against headers
> which are *newer* than the kernel you are running.
>
> There is absolutely no requirement to rebuild anything if you upgrade
> your headers. The breakage of glibc can occur as follows (just to
> provide an example):
>
> 1) You have system-wide linux-headers-2.6.8 and you run kernel-2.6.8.
> All affected packages have been built against those headers.
> 2) You update linux-headers-2.6.8 to linux-headers-2.6.9.
> 3) You _opt_ to rebuild, say, glibc (and yes, it is entirely optional).
> 4) glibc now makes use of kernel API functions which are in advance of
> the kernel you are still running - b0rkage. In this case, you'd either
> have to rebuild glibc against <=linux-headers-2.6.8 or upgrade to
>  >=kernel.2.6.9.
>
> The message that the linux-headers ebuild displays is simply a
> recommendation i.e. "you might like to rebuild glibc now to leverage the
> kernel in so far as possible". It's not mandatory.
>
> > I'd also like to mention that Gentoo is not alone in providing a kernel
> > headers package -- I know Debian and Red Hat do, as well.  However, they
> > have life easier than Gentoo due to its source-based nature.  In binary
> > distributions, they have to rebuild their binary packages when they
> > update the kernel headers, so those get updated as well.
>
> No, they don't have to. The last time I checked, the standard headers
> package in Debian was comparatively ancient - based on a 2.5 snapshot if
> I recall (it's reasonable to assume that these are the headers they use
> when generating their packages). It might not be optimal, but the point
> is this: it doesn't matter from the point of view of functional
> integrity. They make available newer headers packages but there is
> absolutely no requirement for them to rebuild their packages against
> newer headers as long as the standard kernel they ship is not older than
> the headers (which is invariably the case).
>
> Lots of people are running 2.6 kernels on systems that were built with
> 2.4 headers. I've also heard of people running 2.4 kernels on distros
> built with 2.2 headers and it wouldn't surprise me if you could even run
> a 2.6 kernel on a system built with 2.2 headers.
>
> Perhaps some packages may be released that mandate certain headers (for
> example, if they wanted to use the CryptoAPI functions which are only
> available in 2.6 in vanilla terms). In those cases, I'd imagine that
> they would use the "bad" method of traversing /usr/src/linux rather than
> using the system-wide headers, just as 3rd party kernel modules do. I'm
> not aware of any such packages though.
>
> What Linus was complaining about was distros that don't use independent
> system-wide headers at all and, instead, use the hack of symlinking
> /usr/include/linux and /usr/include/asm to their counterparts in a
> kernel source tree. That's a terrible thing to do, it means that any
> package you build that uses kernel headers will be affected according to
> your "kernel du jour" which greatly increases the likelihood of
> breakage. This is why Gentoo uses independent headers which are
> generally *not* a moving target, as does just about any decent distro
> these days. But with Gentoo you still have to ensure that you do not
> upgrade your headers in advance of your kernel version *and* rebuild
> packages against them. This usually isn't an issue; the headers tend to
> be several steps behind any kernel available in portage. The only reason
> it's an issue now is because Gentoo have now pushed 2.6 as part of the
> "default" 2005.0 profile.
>
> Finally, can 2.4 users please not mess around with package.masks and the
> like except where it is strictly necessary. The correct way to do this
> is to link to the 2005.0/2.4 profile as I have mentioned already:
>
> # cd /etc
> # rm make.profile
> # ln -s ../usr/portage/profiles/default-linux/x86/2005.0/2.4 make.profile
>
> Regards,
>
> --Kerin Francis Millar
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