staging: rtl8723bs: use kernel_read() instead of open-coded version

Replace the manual call to f_op->read() under KERNEL_DS with kernel_read().
This also reduces the number of users of the legacy alias get_ds() for
KERNEL_DS.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/os_dep/osdep_service.c

@@ -107,7 +107,7 @@ static int readFile(struct file *fp, char *buf, int len)
 		return -EPERM;
 
 	while (sum<len) {
-		rlen =fp->f_op->read(fp, (char __force __user *)buf+sum, len-sum, &fp->f_pos);
+		rlen = kernel_read(fp, buf + sum, len - sum, &fp->f_pos);
 		if (rlen>0)
 			sum+=rlen;
 		else if (0 != rlen)
@@ -116,7 +116,7 @@ static int readFile(struct file *fp, char *buf, int len)
 			break;
 	}
 
-	return  sum;
+	return sum;
 
 }
 
@@ -129,22 +129,16 @@ static int isFileReadable(char *path)
 {
 	struct file *fp;
 	int ret = 0;
-	mm_segment_t oldfs;
 	char buf;
 
 	fp =filp_open(path, O_RDONLY, 0);
-	if (IS_ERR(fp)) {
-		ret = PTR_ERR(fp);
-	}
-	else {
-		oldfs = get_fs(); set_fs(KERNEL_DS);
+	if (IS_ERR(fp))
+		return PTR_ERR(fp);
 
-		if (1!=readFile(fp, &buf, 1))
-			ret = -EINVAL;
+	if (readFile(fp, &buf, 1) != 1)
+		ret = -EINVAL;
 
-		set_fs(oldfs);
-		filp_close(fp, NULL);
-	}
+	filp_close(fp, NULL);
 	return ret;
 }
 
@@ -158,16 +152,13 @@ static int isFileReadable(char *path)
 static int retriveFromFile(char *path, u8 *buf, u32 sz)
 {
 	int ret =-1;
-	mm_segment_t oldfs;
 	struct file *fp;
 
 	if (path && buf) {
 		if (0 == (ret =openFile(&fp, path, O_RDONLY, 0))) {
 			DBG_871X("%s openFile path:%s fp =%p\n", __func__, path , fp);
 
-			oldfs = get_fs(); set_fs(KERNEL_DS);
 			ret =readFile(fp, buf, sz);
-			set_fs(oldfs);
 			closeFile(fp);
 
 			DBG_871X("%s readFile, ret:%d\n", __func__, ret);