From 0e1104ada32d242bc6169a2ce4eb19ec4febb813 Mon Sep 17 00:00:00 2001
From: Wu Fengguang <fengguang.wu@intel.com>
Date: Fri, 5 Feb 2010 15:00:52 -0500
Subject: /dev/mem: introduce size_inside_page()

commit f222318e9c3a315723e3524fb9d6566b2430db44 upstream

/dev/mem: introduce size_inside_page()

[ cebbert@redhat.com : backport to 2.6.32 ]
[ subset of original patch, for just /dev/kmem ]

Introduce size_inside_page() to replace duplicate /dev/mem code.

Also apply it to /dev/kmem, whose alignment logic was buggy.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Avi Kivity <avi@qumranet.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
 drivers/char/mem.c | 40 +++++++++++++++++-----------------------
 1 file changed, 17 insertions(+), 23 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index a074fceb67d3..1ffb6dd3eae4 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -35,6 +35,19 @@
 # include <linux/efi.h>
 #endif
 
+static inline unsigned long size_inside_page(unsigned long start,
+					     unsigned long size)
+{
+	unsigned long sz;
+
+	if (-start & (PAGE_SIZE - 1))
+		sz = -start & (PAGE_SIZE - 1);
+	else
+		sz = PAGE_SIZE;
+
+	return min_t(unsigned long, sz, size);
+}
+
 /*
  * Architectures vary in how they handle caching for addresses
  * outside of main memory.
@@ -430,15 +443,7 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
 		}
 #endif
 		while (low_count > 0) {
-			/*
-			 * Handle first page in case it's not aligned
-			 */
-			if (-p & (PAGE_SIZE - 1))
-				sz = -p & (PAGE_SIZE - 1);
-			else
-				sz = PAGE_SIZE;
-
-			sz = min_t(unsigned long, sz, low_count);
+			sz = size_inside_page(p, low_count);
 
 			/*
 			 * On ia64 if a page has been mapped somewhere as
@@ -462,10 +467,8 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
 		if (!kbuf)
 			return -ENOMEM;
 		while (count > 0) {
-			int len = count;
+			int len = size_inside_page(p, count);
 
-			if (len > PAGE_SIZE)
-				len = PAGE_SIZE;
 			len = vread(kbuf, (char *)p, len);
 			if (!len)
 				break;
@@ -510,15 +513,8 @@ do_write_kmem(void *p, unsigned long realp, const char __user * buf,
 
 	while (count > 0) {
 		char *ptr;
-		/*
-		 * Handle first page in case it's not aligned
-		 */
-		if (-realp & (PAGE_SIZE - 1))
-			sz = -realp & (PAGE_SIZE - 1);
-		else
-			sz = PAGE_SIZE;
 
-		sz = min_t(unsigned long, sz, count);
+		sz = size_inside_page(realp, count);
 
 		/*
 		 * On ia64 if a page has been mapped somewhere as
@@ -578,10 +574,8 @@ static ssize_t write_kmem(struct file * file, const char __user * buf,
 		if (!kbuf)
 			return wrote ? wrote : -ENOMEM;
 		while (count > 0) {
-			int len = count;
+			int len = size_inside_page(p, count);
 
-			if (len > PAGE_SIZE)
-				len = PAGE_SIZE;
 			if (len) {
 				written = copy_from_user(kbuf, buf, len);
 				if (written) {
-- 
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