Linux-kernel mailing list archive 1999-37,: Re: High Performance I/O stuff (more)

# Re: High Performance I/O stuff (more)

Stephen C. Tweedie (sct@redhat.com)
Wed, 15 Sep 1999 18:59:53 +0100 (BST)

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Hi,

On Wed, 15 Sep 1999 00:06:59 -0700, "Jayson Nordwick"
<nordwick@scam.xcf.berkeley.edu> said:

> Now, looking at POSIX.1b signals and signal queues and getting some
> information from Stephen Tweedie it looks like completion ports are doable
> without anything new, I think that I have decided.

You are missing the point...

> If you find an available signal, set the handler for it, the block it,
> this signal number now effectively becomes the completion port. You then
> can fcntl() a file descriptor with F_SETSIG and the signal number. Then to
> fetch the blocked signals, use sigwaitinfo().

The point is that this _already works_. You get the fd in the
siginfo's si_fd struct. What is missing right now is poll band
information for si_band, but there are patches pending for that.

> The one drawback that I see to this is that it can only really handle
> aio_{read,write}() and {read,write}()/fcntl(). Any other events such as
> thread/child deaths cannot really be worked into this scheme unless you
> could set the signal they deliver on termination.

Completion ports also don't implement things like child death
notification until you implement child death notification completion
ports. :) We already have a working model: if you want to add more
completion events, then feel free to do so. You don't need to invent
a new delivery mechanism.

> If you really wanted to, you could have signals delivered for the ability
> to read/write to a file descriptor and then you would have Gaurav's model.

That is what happens today. We already have that model. That is what
F_SETSIG does.

> Basically, unless anybody can see anything wrong with this get to work
> implementing!

I already implemented it --- it is in 2.2.

--Stephen

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