Re: /usr/include/linux, /usr/include/asm, ...
I'll reverse the question: why are you using the links?
The links are ignored anyway while compiling the kernel, so that's
not it. However, you may totally confuse some other program (during
compilation) that does not expect changes that are made in the kernel
includes. You see, changes may be made in kernel headers in concert
with other include files, which have not been upgraded, files that
are not required for kernel builds, but may be required for package
So, what else are the links good for? Most programs do not
(and should not) depend on kernel version specific api's; and the
handful that do should ask for and include -I/usr/src/linux anyway.
Please also see the canned response below.
The headers were included in libc5-dev after a rash of very
buggy alpha kernel releases (1.3.7* or something like that) that
proceeded to break compilations, etc. Kernel versions are changed
far more rapidly than libc is, and there are higer chances that
people install a custom kernel than they install custom libc.
The kernel headers used to make sense exporting to user space,
but the user space thing has grown so much that it's really not
practical any more. And technically, the symlinks really aren't very
As of glibc, the kernel headers will really be _kernel_
headers, and user level includes are user level includes, because it
is no longer possible to try to synchronize the libc and the kernel
the way it used to be. The symlinks have been a bad idea for at least
a year now, and the problem is just how to get rid of them
The _only_ reason for the symlinks is to immediately give
access to new features in the kernel when those happen. New ioctl
numbers etc etc. That was an overriding concern early on: the kernel
interfaces expanded so rapidly even in "normal" areas that having the
synchronization that symlinks offered was a good thing.
However, the kernel interfaces aren't really supposed to
change all that quickly any more, and more importantly: the technical
users know how to fix things any way they want, so if they want a new
ioctl number to show up they can actually edit the header files
themselves, for example. But having separation is good for the
non-technical user, because there are less surprises and package
Add to that the fact that few programs really need the more
volatile elements of the header files (that is, things that really
change from kernel version to kernel version), [before you reject
this, consider: programs compiled on one kernel version usually work
on other kernels].
So, it makes sense that a set of headers be provided from a
known good kernel version, and that is sufficient for compiling most
programs, (it also makes the compile time environments for programs
on debian machines a well known one, easing the process of dealing
with problem reports), the few programs that really depend on cutting
edge kernel data structures may just use -I/usr/src/linux/include
(provided that kernel-headers or kernel-source exists on the system).
Most programs, even if they include <linux/something.h>, do
not really depend on the version of the kernel, as long as the kernel
versions are not too far off, they will work. And the headers
provided in libc5-dev are just that.
libc5-deb is uploaded frequently enough that it never lags too
far behind the latest released kernel.
There are two different capabilities which are the issue, and
the kernel-packages and libc5-dev address different ones:
a) The kernel packages try to provide a stable, well behaved kernel
and modules, and may be upgraded whenever there are significant
advances in those directions (bug fixes, more/better module
support, etc). These, however, may not have include files that
are non-broken as far as non-kernel programs are concerned, and
the quality of the development/compilation environment is not the
kernel packages priority (Also, please note that the kernel
packages are tied together, so kernel-source, headers, and image
are produced in sync)
b) Quality of the development/compilation environment is the priority
of libc5-dev package, and it tries to ensure that the headers it
provides would be stable and not break non-kernel programs. This
assertion may fail for alpha kernels, which may otherwise be
perfectly stable, hence the need for a different set of known-good
kernel include files.
Marriage is a three ring circus: The engagement ring, the wedding
ring, and the suffering.
Manoj Srivastava <url:mailto:email@example.com>
Mobile, Alabama USA <url:http://www.datasync.com/%7Esrivasta/>
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