On 05/18/2015 02:53 AM, Arnd Bergmann 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?
It seems to work, except I don't really understand why there is a difference between (b) and (c).
I also have no problem just having klibc contain its own definitions of these structures, as long as one can prevent the kernel from defining them.
-hpa