From: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Date: Thu, 20 May 2010 13:35:22 +0000 (-0400)
Subject: Serialize access to global structure using semaphore.
X-Git-Url: http://git.cascardo.eti.br/?p=cascardo%2Fkernel%2Fsamples%2Fchar2%2F.git;a=commitdiff_plain;h=76680d10903416190497df7dc25d4469401c53bb

Serialize access to global structure using semaphore.
---

diff --git a/hellochar.c b/hellochar.c
index 71605f6..85510f7 100644
--- a/hellochar.c
+++ b/hellochar.c
@@ -20,6 +20,7 @@
 #include <linux/fs.h>
 #include <linux/cdev.h>
 #include <linux/slab.h>
+#include <linux/semaphore.h>
 #include <asm/uaccess.h>
 
 MODULE_LICENSE("GPL");
@@ -33,16 +34,19 @@ struct hello_buffer {
 	size_t len;
 	char buffer[0];
 };
-struct hello_buffer *hello;
+static struct hello_buffer *hello;
+static DECLARE_MUTEX(hello_mtx);
 
 static int hello_open(struct inode *ino, struct file *fp)
 {
+	down(&hello_mtx);
 	if (fp->f_flags & O_TRUNC) {
 		memset(hello->buffer, 0, MAXLEN);
 		hello->len = 0;
 	}
 	if (fp->f_flags & O_APPEND)
 		fp->f_pos = hello->len;
+	up(&hello_mtx);
 	return 0;
 }
 
@@ -50,9 +54,11 @@ static ssize_t hello_read(struct file *fp, char __user *buf, size_t sz,
 	loff_t *pos)
 {
 	int r;
+	down(&hello_mtx);
 	if (sz + *pos > hello->len)
 		sz = hello->len - *pos;
 	r = copy_to_user(buf, hello->buffer + *pos, sz);
+	up(&hello_mtx);
 	if (r)
 		return -EFAULT;
 	*pos += sz;
@@ -63,14 +69,18 @@ static ssize_t hello_write(struct file *fp, const char __user *buf, size_t sz,
 	loff_t *pos)
 {
 	int r;
+	down(&hello_mtx);
 	if (sz + *pos > MAXLEN)
 		sz = MAXLEN - *pos;
 	r = copy_from_user(hello->buffer + *pos, buf, sz);
-	if (r)
+	if (r) {
+		up(&hello_mtx);
 		return -EFAULT;
+	}
 	*pos += sz;
 	if (hello->len < *pos)
 		hello->len = *pos;
+	up(&hello_mtx);
 	return sz;
 }