48 lines
2.2 KiB
Text
48 lines
2.2 KiB
Text
This is a small library that implements epoll on top of kqueue. It
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has been successfully used to port libinput, libevdev, Wayland and
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more software to FreeBSD: https://www.freshports.org/devel/libepoll-shim/
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It may be useful for porting other software that uses epoll as well.
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The library provides implementation of Linux timerfd_create(2) related
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APIs, eventfd(2), signalfd(2).
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However, this library contains some very ugly hacks and workarounds.
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For example:
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- When using timerfd, signalfd or eventfd, the system calls read,
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write and close are redefined as macros to internal helper
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functions. This is needed as there is some internal context that
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has to be free'd properly. This means that you shouldn't create
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a timerfd/signalfd in one part of a program and close it in a
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different part where sys/timerfd.h isn't included. The context
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would leak. Luckily, software such as libinput behaves very nicely
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and puts all timerfd related code in a single source file.
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- There is limited support for file descriptors that lack support
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for kqueue but are supported by poll(2). This includes graphics
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or sound devices under /dev. Those descriptors are handled in an
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outer poll(2) loop. Edge triggering using EPOLLET will not work.
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- Shimmed file descriptors cannot be shared between processes. On
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fork() those fds are closed. When trying to pass a shimmed fd to
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another process the sendmsg call will return EOPNOTSUPP. In most
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cases sharing epoll/timerfd/signalfd is a bad idea anyway, but
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there are some legitimate use cases (for example sharing semaphore
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eventfds, issue #23). When the OS natively supports eventfds (as
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is the case for FreeBSD >= 13) this library won't provide eventfd
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shims or the sys/eventfd.h header.
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- There is no proper notification mechanism for changes to the
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system CLOCK_REALTIME clock on BSD systems. Also, kevent
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EVFILT_TIMERs use the system monotonic clock as reference.
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Therefore, in order to implement absolute (TFD_TIMER_ABSTIME)
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CLOCK_REALTIME timerfds or cancellation support
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(TFD_TIMER_CANCEL_ON_SET), a thread is spawned that periodically
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polls the system boot time for changes to the realtime clock.
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The following operating systems are supported:
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FreeBSD >= 11.4, >= 12.2, >= 13.0
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NetBSD >= 9.1
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OpenBSD >= 6.7
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