I suspect that if I compile the following using gcc-9 It'll bleat
about going beyond the end of the array:
#define _GNU_SOURCE
#include <sched.h>
#define MAX_CPU 2048
int fubar(void)
{
cpu_set_t *set = CPU_ALLOC(MAX_CPU);
CPU_SET_S(MAX_CPU - 2, CPU_ALLOC_SIZE(MAX_CPU), set);
return CPU_COUNT_S(CPU_ALLOC_SIZE(MAX_CPU), set);
}
I can't test since I don't have a copy of gcc-9.
The whole interface for > 1024 cpus looks horrid though.
Reading version 5.01 on the man page.
I'd have thought that if the application provided a short mask
to sched_setaffinity() the rest would be deemed to be zeros.
And that if an overlong mask is passed to sched_getaffinity()
the extra bytes/longs would either be zerod or unchanged.
Be aware that CPU_ALLOC(3) may allocate a slightly larger CPU set
than requested (because CPU sets are implemented as bit masks
allocated in units of sizeof(long)). Consequently,
sched_getaffinity() can set bits beyond the requested allocation
size, because the kernel sees a few additional bits. Therefore, the
caller should iterate over the bits in the returned set, counting
those which are set, and stop upon reaching the value returned by
CPU_COUNT(3) (rather than iterating over the number of bits requested
to be allocated).
A short mask to sched_getaffinity() should also do something
more sensible than just returning an error.
David
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