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usermode, using shared page. The structures and functions have vdso prefix, to indicate the intended location of the code in some future. The versioned per-algorithm data is exported in the format of struct vdso_timehands, which mostly repeats the content of in-kernel struct timehands. Usermode reading of the structure can be lockless. Compatibility export for 32bit processes on 64bit host is also provided. Kernel also provides usermode with indication about currently used timecounter, so that libc can fall back to syscall if configured timecounter is unknown to usermode code. The shared data updates are initiated both from the tc_windup(), where a fast task is queued to do the update, and from sysctl handlers which change timecounter. A manual override switch kern.timecounter.fast_gettime allows to turn off the mechanism. Only x86 architectures export the real algorithm data, and there, only for tsc timecounter. HPET counters page could be exported as well, but I prefer to not further glue the kernel and libc ABI there until proper vdso-based solution is developed. Minimal stubs neccessary for non-x86 architectures to still compile are provided. Discussed with: bde Reviewed by: jhb Tested by: flo MFC after: 1 month
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