How does one check if a file descriptor is guarded? Is there any guarded FD numbers that are determinate? I've seen 12 being NPOLICY in a few things -- is there documentation for which FDs might be guarded? Thanks. The platform is Mac Catalyst.
What are you trying to do here?
Generally it doesn’t make sense to test whether a file descriptor is guarded because:
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Either the file descriptor is something you guarded, in which case you already know the answer.
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Or it’s not, in which case the check is subject to the very TOC/TOU issues that guards protect against.
Is there any guarded FD numbers that are determinate?
No. In general the only determinate file descriptors are 0, 1, and 2 for std{in,out,err}.
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