Stefan Beller <sbeller@xxxxxxxxxx> writes:
> So if we get an EAGAIN or EWOULDBLOCK error the fd must be nonblocking.
> As the intend of xread is to read as much as possible either until the
> fd is EOF or an actual error occurs, we can ease the feeder of the fd
> by not spinning the whole time, but rather wait for it politely by not
> busy waiting.
As you said in the cover letter, this does look questionable. It is
sweeping the problem under the rug (the hard-coded 100ms is a good
clue to tell that). If the caller does want us to read thru to the
end, then we would need to make it easier for such a caller to stop
marking the file descriptor to be non-blocking, but this does not do
anything to help that. An alternative might be to automatically
turn nonblocking off temporarily once we get EAGAIN (and turn it on
again before leaving); that would be an approach to make it
unnecessary to fix the caller (which has its own set of problems,
though).
> + if (i < 0) {
> + if (errno == EINTR || errno == ENOMEM)
> + continue;
I can sort of see EINTR but why is ENOMEM any special than other
errors?
> + else
> + die_errno("poll");
> + }
> + }
> + }
> return nr;
> }
> }
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