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epoll: Store epoll_event udata member in ext member of kevent.
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Authored by wulf on Jan 14 2021, 8:51 PM.

Details

Summary

Current epoll implementation stores udata fields of epoll_event
structure in special dynamically-sized table rather than in udata field
of backing kevent structure because of 2 reasons:

  1. Kevent's udata size is smaller than epoll's on 32-bit archs.
  2. Kevent's udata can be clobbered on execution EPOLL_CTL_ADD as kqueue modifies existing event while epoll returns error in this case.

After r320043 has introduced 4 new 64bit user data members (ext[]),
we can store epoll udata in one of them and drop aforementioned table.
According to kqueue_register() source code ext members are not updated
when existing kevent is modified that fixes p.2.

As a side effect the patch fixes PR/252582.

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Repository
R10 FreeBSD src repository
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