Re: [RFC PATCH 0/3] epoll: read(),write(),ioctl() interface

From: Nathaniel Yazdani
Date: Mon Feb 03 2014 - 14:34:46 EST

On 2/3/14, Clemens Ladisch <clemens@xxxxxxxxxx> wrote:
> Nathaniel Yazdani wrote:
>> Using the normal I/O interface to manipulate eventpolls is much neater
>> than using epoll-specific syscalls
> But it introduces a _second_ API, which is epoll-specific too, and does
> not use the standard semantics either.
>> while also allowing for greater flexibility (theoretically, pipes could
>> be used to filter access).
> I do not understand this.

The idea here was that if epoll is controlled by read()/write(), then
a program could be written so that it expects the epoll to dup()ed
to a second file descriptor, using one exclusively for writing & the
other exclusively for reading. That way, if an application is in
debug mode, for example, it could start up a thread to replace
those two file descriptors with pipes, so that thread would then
be able to tee, preprocess, or do whatever else to the epoll

>> read() simply waits for enough events to fill the provided buffer.
> The usual semantics of read() are to return a partially filled buffer if
> it would block otherwise, i.e., blocking is done only if the returned
> buffer would have been empty.
>> As timeout control is essential for polling to be practical, ioctl() is
>> used to configure an optional timeout
> This is what the timeout parameter of poll() and friends is for.

I admit that part of this approach isn't the best.

Either way I appreciate your feedback,
Nathaniel Yazdani
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