Map epoll_ctl() errors through php_poll_errno_to_error()

[nicolas-grekas]

The epoll backend reports everything but EEXIST and ENOENT as ERR_SYSTEM, so a caller cannot tell "this handle cannot be polled" from "polling is broken". The kqueue backend already maps errno through php_poll_errno_to_error(), this makes epoll do the same.

EPERM gets its own case: epoll_ctl() returns it for files that do not implement polling, which means Context::add() fails for regular files, php://temp and /dev/null while Backend::Poll accepts them all:

                    Auto (epoll)                      Poll
regular file        FailedHandleAddException          added ok
/dev/null           FailedHandleAddException          added ok
php://temp          FailedHandleAddException          added ok
pipe                added ok                          added ok
socketpair          added ok                          added ok

That is expected from epoll, and kqueue does not have the problem since it takes regular files. But an event loop has to deal with it, since STDIN is /dev/null in most CI runs and a plain file whenever it is redirected, and today the only way to detect the case is to try the handle again on a Backend::Poll context. With ERROR_NOSUPPORT it can fall back on the spot.

/cc @bukka

[bukka]

It makes sense.

[bukka]

The CI failures seemed unrelated btw.

[nicolas-grekas]

Cool, thanks for merging my PRs !