selscan asks a descriptor once, with the flags of every set it is in (POLLRDNORM for the read set, POLLWRNORM for the write set, POLLRDBAND for the exception set, plus POLLHUP and POLLERR), and marks each set whose flags the answer shares. A seeded random device's randomdev_poll narrows a request with POLLRDNORM to that bit and returns any other request whole, so in the read set it is readable and in no other set, and otherwise it is in each write and exception set it was asked in; select reported it readable and writable together and never exceptional. A regular file or directory went to the host poll, which on Windows threw; vop_stdpoll makes it readable and writable and never exceptional, which select now answers in process on every host, as poll does.
Alexej Szpevák
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