Messages in this thread |  | | Date | Mon, 11 Dec 2000 19:53:05 -0600 | Subject | Re: PATCH: linux-2.4.0-test12pre8/include/linux/module.h breaks sysklogd compilation | From | Peter Samuelson <> |
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[Mohammad A. Haque] > Wasn't there discussion that user space apps shouldn't include kernel > headers?
Oh, it's been discussed, many times. Here is my executive summary of why nobody needs to use kernel headers in userspace programs, *EVER*:
Q: I want to #include <linux/foo.h> but I get compile errors, please apply this patch to foo.h.
A: Make a copy of foo.h, fix it up to compile properly in your application and ship it in your tarball.
Q: What if foo.h changes? My copy will be out of date and my app will not work properly on new kernels.
A: This is exactly the same problem as userspace ABI drift. And it has exactly the same solution: make sure userspace interfaces to kernel functionality are as stable as possible. We really *do* try not to gratuitously break binaries ... except certain system utilities which are low-level enough to justify telling the user to upgrade (and that's a short list -- see Documentation/Changes.)
Q: What about new features? What if foo.h gets some new ioctl definitions? My copy won't have these and my app won't be able to use them.
A: So resync with the kernel copy, when the need arises. Obviously your app won't magically be able to just use the new functionality without other changes on your part -- resyncing foo.h is just a small part of the changes you are already making anyway.
Q: I maintain a subsystem with tightly-coupled userspace and kernel components.
A: So maintain *your* header files however you wish, but just ship separate copies in your kernel patches and userspace tarballs.
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