linux-kernel - Re: [PATCH] pipe: don't block after data has been written

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Message-ID: <20091105162043.GA2611@hack>
Date:	Fri, 6 Nov 2009 00:20:44 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Max Kellermann <max@...mpel.org>
Cc:	linux-kernel@...r.kernel.org, eric.dumazet@...il.com, mk@...all.com
Subject: Re: [PATCH] pipe: don't block after data has been written

On Thu, Nov 05, 2009 at 04:31:47PM +0100, Max Kellermann wrote:
>According to the select() / poll() documentation, a write operation on
>a file descriptor which is "ready for writing" must not block.  Linux
>violates this rule: if you pass a very large buffer to write(), the
>system call will not return until everything is written, or an error
>occurs.
>
>This patch adds a simple check: if at least one byte has already been
>written, break from the loop, instead of calling pipe_wait().

Do you have any working test-case for this?

Thanks.

>
>Signed-off-by: Max Kellermann <max@...mpel.org>
>---
>
> fs/pipe.c |    2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
>diff --git a/fs/pipe.c b/fs/pipe.c
>index ae17d02..9d84f0b 100644
>--- a/fs/pipe.c
>+++ b/fs/pipe.c
>@@ -582,7 +582,7 @@ redo2:
> 		}
> 		if (bufs < PIPE_BUFFERS)
> 			continue;
>-		if (filp->f_flags & O_NONBLOCK) {
>+		if (filp->f_flags & O_NONBLOCK || ret > 0) {
> 			if (!ret)
> 				ret = -EAGAIN;
> 			break;
>
>--
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