linux-kernel - Re: PROPOSAL: extend pipe() to support NULL argument.

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Message-ID: <20090703051917.GE5880@cr0.nay.redhat.com>
Date:	Fri, 3 Jul 2009 13:19:17 +0800
From:	Amerigo Wang <xiyou.wangcong@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Amerigo Wang <xiyou.wangcong@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: PROPOSAL: extend pipe() to support NULL argument.

On Fri, Jul 03, 2009 at 12:08:58PM +0800, Changli Gao wrote:
>On Fri, Jul 3, 2009 at 11:00 AM, Amerigo Wang<xiyou.wangcong@...il.com> wrote:
>>
>> When I said 'pipe', I meant *anonymous* pipe, definitely!
>> There is nothing related with *named* pipe here.
>>
>Pipe means *anonymous* pipe? Who defined that? What the difference
>between an anonymou pipe and a named pipe? Two ends or one ends? I
>don't think so. Having explicit name is the right difference between
>them.

I have no interests to teach you its definition.

if you re-read my email, you should conclude what 'pipe' there means,
according to the contexts.

>
>And when I said 'kernel buffer handler', I means it is not a
>traditional pipe, and I just extend and reuse the pipe API to create a
>kernel buffer handler for splicing use.


What pipe(2) creates is exactly an *anonymous* pipe.

>
>> You are going to a *wrong* direction.
>>
>What is the right direction you think? Keep the pipe() API unchanged
>and keep two fds refering to the same kernel buffer? If you want to
>keep the API unchanged just for compatiblity with POSIX, I agree with
>you, and maybe a new system call is needed.


Yes, exactly.
Inventing a new API is better than modifying pipe(2), IMO.

BUT I still don't agree that you really need this... I think you
can add a flag or something like that to an fd to do this, e.g.

   fcntl(fd, F_SETFD, FD_PIPERW);

Isn't this better?

>
>>
>> If you repeat your (pipe,splice,splice,close,close) sequence for
>> thousands times, it is still the same, nothing saves...
>>
>You means that?
>
>while (<condition>) {
> pipe/splice/splice/close/close?
>}

At least this is what I understand from your words.

>
>You don't know my meaning. As a proxy server, there maybe lots of
>connections to maintain, and these connections will keep open for a
>long time. If the data received can be sent in a relay cycle, the
>kernel buffer can be reused. If not, the kernel buffer must be
>reserved. When there are lots of these kinds of connections, lots of
>kernel buffers must be reserved. At this time, whether two fds per
>kernel buffer or one fds per kernel buffer matters.

SHow us the code, please.
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