epoll'ing tcp sockets for reading

[Nikolai ZHUBR <zhubr@mail.ru>]

Hello people, I have a question about epoll'ing tcp sockets.

Is it possible (with epoll or some other good method) to get userspace
notified not only of the fact that some data has become available
for the socket, but also of the respective _size_ available for
reading connected with this exact event?

Yes, read'ing until EAGAIN or using FIONREAD would provide this
sort of information, but there is a problem. In case of subsequent
continuous data arrival, an application could get stuck reading
data for one socket infinitely (after epoll return, just before
the next epoll), unless it implements some kind of artifical safety
measures.

To my understanding, EPOLLONESHOT does not suffice here, because
it only "fixes" the epoll'ing part but not the read'ing part, whereas
_both_ epoll'ing and read'ing appear to be responsible. Therefore,
"event atomicity" is lost anyway. Or am I wrong?

(Please CC me, I'm not subscribed)

Thank you!

Nikolai ZHUBR