On 04/11/2013 04:44 PM, Johannes Berg wrote: > On Wed, 2013-04-10 at 19:15 +0200, Johannes Berg wrote: > >>> Sure, lets what's the idea or do you want to do that on another thread? > > Let me give it a different subject :-) > >> It's kinda half-baked and I'm not completely sure it's a good idea >> (because we may have to follow header file renames, though they happen >> rarely), but I was basically thinking this: >> >> Say there's >> >> void my_foo_function(struct foo *f); >> >> that we want to backport. Let's also say it's defined in <linux/foo.h>, >> and that it was usually present starting from kernel 3.0, but for now >> let's assume the "foo" subsystem always existed (i.e. <linux/foo.h>) >> >> Typically, we'd therefore add it to <linux/compat-3.0.h> and declare it >> there, maybe with the LINUX_BACKPORT() wrapper, and then define it in >> compat/compat-3.0.c. >> >> What I'm thinking is that we should maybe declare it in compat in >> include/linux/foo.h instead, maybe like this: >> >> #ifndef __BACKPORT_FOO >> #define __BACKPORT_FOO >> #include_next <linux/foo.h> >> >> #if LINUX_VERSION < 3.0 >> #define my_foo_function LINUX_BACKPORT(my_foo_function) >> >> void my_foo_function(struct foo *f); >> #endif >> >> #endif /* __BACKPORT_FOO */ >> >> >> >> I'm a bit undecided. On the one hand I think it's nice that we can spot >> in one place what's backported where in all the >> include/linux/compat-xyz.h files, but on the other hand it's kinda >> becoming a messy jumble of features across different subsystems, and >> hard to determine what you have already and might need for a given >> header file? > > In addition to what I said, I just realized that we should probably do > this, and do it consistently even for old things. That way, we can get > rid of all the pr_fmt patches. > > The reason for the pr_fmt patches is that typically, a source file would > have > > #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > #include <whatever, including somehow getting printk.h> > > Now that we force them to include compat-2.6.h at the very beginning of > the file, printk.h already gets included in some way through > compat-2.6.h (there are of course MANY MANY paths to it.) > > To avoid redefine warnings, we thus patch everything to be > > #undef pr_fmt > #define pr_fmt > ... > > which of course works, but it's pretty ugly (we have >1000 patchlines > for this!) > > > If we were able to get rid of compat-2.6.h and put all the backports > into their appropriate headers (linux/foo.h) we could only force an > include of compat_autoconf.h (which doesn't include printk.h of course) > and then we'd be able to get rid of all these patches. I had a similar same idea a year ago, but haven't found the time to complete it, see [0]. I am still for this solution. If linux/foo.h does not exist in recent kernel versions we have to add it anyway, because the new code references it, so this is not a problem. With this solution we would clean up the includes used when compiling and we do not need the pr_fmt patch any more and hopefully some more. Hauke [0]: https://lists.linuxfoundation.org/pipermail/lf_driver_backport/2012-April/000972.html -- To unsubscribe from this list: send the line "unsubscribe backports" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
