linux-kernel - [PATCH] fs: make simple_read_from

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Message-ID: <alpine.DEB.2.00.0903040002180.7995@gandalf.stny.rr.com>
Date:	Wed, 4 Mar 2009 00:07:07 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
cc:	Theodore Tso <tytso@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Pekka Paalanen <pq@....fi>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Martin Bligh <mbligh@...gle.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Jason Baron <jbaron@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jiaying Zhang <jiayingz@...gle.com>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	mrubin@...gle.com, md@...gle.com,
	Steven Rostedt <srostedt@...hat.com>
Subject: [PATCH] fs: make simple_read_from_buffer conventional


Impact: have simple_read_from_buffer conform to standards

It was brought to my attention by Andrew Morton, Theodore Tso,
and H. Peter Anvin that a read from userspace should only return
-EFAULT if nothing was actually read.

Looking at the simple_read_from_buffer I noticed that this function
does not conform to that rule. This patch fixes that function.

Signed-off-by: Steven Rostedt <srostedt@...hat.com>

diff --git a/fs/libfs.c b/fs/libfs.c
index 49b4409..6a72298 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -525,14 +525,20 @@ ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
 				const void *from, size_t available)
 {
 	loff_t pos = *ppos;
+	size_t ret;
+
 	if (pos < 0)
 		return -EINVAL;
 	if (pos >= available)
 		return 0;
 	if (count > available - pos)
 		count = available - pos;
-	if (copy_to_user(to, from + pos, count))
-		return -EFAULT;
+	ret = copy_to_user(to, from + pos, count);
+	if (ret) {
+		if (ret == count)
+			return -EFAULT;
+		count -= ret;
+	}
 	*ppos = pos + count;
 	return count;
 }

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