On Mon, May 18, 2015 at 2:53 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > In the patch series I posted recently [1], I introduce new system calls to deal > with modified data structures, but left the question open on how these should > be best accessed from libc. The patches introduce a new __kernel_time64_t type > and based on that five new data structured: struct __kernel_timespec, > struct __kernel_itimerspec, struct __kernel_stat, struct __kernel_rusage, > and struct __kernel_timex. This works fine for the case when all libc > implementations provide their own definitions to user space, but not for > the simplest case (e.g. klibc) where the user-visible structures come directly > from the kernel uapi headers. > > I still don't know what model the various libc developers prefer, so here is > an alternative approach, as a patch on top of the previous series: > > Now, we rename the original structures to struct __old_kernel_*, and use a > macro to define either the __old_kernel_* or the __kernel_* structure name > to the name we actually want in user space, based on a __KERNEL_TIME_BITS > macro that can be set to either 32 or 64 for 32-bit architectures by > the libc. Depending on that macro, the compiler will either see one > of these combinations (for each of the five structures): > > a) __BITS_PER_LONG == 32 && __KERNEL_TIME_BITS == 32: > > struct timespec based on 32-bit __kernel_time_t > struct __kernel_timespec based on 64-bit __kernel_time64_t > > b) __BITS_PER_LONG == 64 && __KERNEL_TIME_BITS == 64: > > struct timespec based on 64-bit __kernel_time_t > struct __kernel_timespec based on 64-bit __kernel_time64_t > > c) __BITS_PER_LONG == 32 && __KERNEL_TIME_BITS == 64: > > struct __old_kernel_timespec based on 32-bit __kernel_time_t > struct timespec based on 64-bit __kernel_time64_t > > Would this work for everyone? Any alternative suggestions? > > Arnd > > [1] http://git.kernel.org/cgit/linux/kernel/git/arnd/playground.git/log/?h=y2038-syscalls > https://lwn.net/Articles/643407/ > > diff --git a/include/uapi/asm-generic/bitsperlong.h b/include/uapi/asm-generic/bitsperlong.h > index 23e6c416b85f..ecdaf4f77f35 100644 > --- a/include/uapi/asm-generic/bitsperlong.h > +++ b/include/uapi/asm-generic/bitsperlong.h > @@ -12,4 +12,13 @@ > #define __BITS_PER_LONG 32 > #endif > > +/* > + * Traditionally we define defines 'time_t' as 'long', but we need to > + * migrate to a 64-bit type until 2038. This one is designed to be > + * overridden by user space if it's prepared to handle 64-bit time_t. > + */ > +#ifndef __KERNEL_TIME_BITS > +#define __KERNEL_TIME_BITS __BITS_PER_LONG > +#endif > + > #endif /* _UAPI__ASM_GENERIC_BITS_PER_LONG */ > diff --git a/include/uapi/asm-generic/kernel_stat.h b/include/uapi/asm-generic/kernel_stat.h > index d1db22583046..3693496c78aa 100644 > --- a/include/uapi/asm-generic/kernel_stat.h > +++ b/include/uapi/asm-generic/kernel_stat.h > @@ -1,6 +1,14 @@ > #ifndef __ASM_GENERIC_KERNEL_STAT_H > #define __ASM_GENERIC_KERNEL_STAT_H > > +#include <asm/bitsperlong.h> > + > +#if __KERNEL_TIME_BITS == 32 || __BITS_PER_LONG == 64 > +#define __old_kernel_stat2 stat > +#else > +#define __kernel_stat stat > +#endif > + > /* > * The new structure that works on both 32-bit and 64-bit and survives y2038 > * The layout matches 'struct stat' from asm-generic/stat.h on 64-bit > diff --git a/include/uapi/asm-generic/stat.h b/include/uapi/asm-generic/stat.h > index 64c32ba7c1a9..f66b28b96c8d 100644 > --- a/include/uapi/asm-generic/stat.h > +++ b/include/uapi/asm-generic/stat.h > @@ -22,7 +22,7 @@ > > #define STAT_HAVE_NSEC 1 > > -struct stat { > +struct __old_kernel_stat2 { > unsigned long st_dev; /* Device. */ > unsigned long st_ino; /* File serial number. */ > unsigned int st_mode; /* File mode. */ > diff --git a/include/uapi/linux/resource.h b/include/uapi/linux/resource.h > index c4f3ba44db00..9a3876cc4436 100644 > --- a/include/uapi/linux/resource.h > +++ b/include/uapi/linux/resource.h > @@ -3,10 +3,16 @@ > > #include <linux/time.h> > #include <linux/types.h> > +#include <asm/bitsperlong.h> > > /* > * Resource control/accounting header file for linux > */ > +#if __KERNEL_TIME_BITS == 32 || __BITS_PER_LONG == 64 > +#define __old_kernel_rusage rusage > +#else > +#define __kernel_rusage rusage > +#endif This all looks ok to me. Though I wonder if it would be cleaner to have all these conditional definitions in one header, rather then littered about in a ton of files. I'm torn because having the definitions close to the underlying structure helps folks reading through the code, but it still seems a little bit messy. thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
