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

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Message-ID: <20091105153147.27473.19570.stgit@woodpecker.roonstrasse.net>
Date:	Thu, 05 Nov 2009 16:31:47 +0100
From:	Max Kellermann <max@...mpel.org>
To:	linux-kernel@...r.kernel.org
Cc:	eric.dumazet@...il.com, mk@...all.com
Subject: [PATCH] pipe: don't block after data has been written

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().

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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