[RFC PATCH 2/4] vhost: add byteswap routines

[Cédric Le Goater <clg@xxxxxxxxxx>]

This patch adds a few helper routines around get_user and put_user
to ease byteswapping.

Signed-off-by: Cédric Le Goater <clg@xxxxxxxxxx>
---

I am not sure these routines belong to this file. There is room for 
improvement to remove the ugly  switch (sizeof(*(ptr))). Please 
comment !

 drivers/vhost/vhost.c |   93 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 72c21b790ba3..afcb3368370c 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -25,6 +25,7 @@
 #include <linux/kthread.h>
 #include <linux/cgroup.h>
 #include <linux/module.h>
+#include <linux/swab.h>
 
 #include "vhost.h"
 
@@ -1001,6 +1002,98 @@ int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
 }
 EXPORT_SYMBOL_GPL(vhost_log_write);
 
+#define vq_get_user(vq, x, ptr)					\
+({								\
+	int ret = get_user(x, ptr);				\
+	if (vq->byteswap) {					\
+		switch (sizeof(*(ptr))) {			\
+		case 2:						\
+			x = swab16(x);				\
+			break;					\
+		case 4:						\
+			x = swab32(x);				\
+			break;					\
+		case 8:						\
+			x = swab64(x);				\
+			break;					\
+		default:					\
+			break;					\
+		}						\
+	}							\
+	ret;							\
+})
+
+#define vq_put_user(vq, x, ptr)					\
+({								\
+	__typeof__(*(ptr)) y = (x);				\
+	if (vq->byteswap) {					\
+		switch (sizeof(*(ptr))) {			\
+		case 2:						\
+			y = swab16(x);				\
+			break;					\
+		case 4:						\
+			y = swab32(x);				\
+			break;					\
+		case 8:						\
+			y = swab64(x);				\
+			break;					\
+		default:					\
+			break;					\
+		}						\
+	}							\
+	put_user(y, ptr);					\
+})
+
+#define __vq_get_user(vq, x, ptr)					\
+({								\
+	int ret = __get_user(x, ptr);				\
+	if (vq->byteswap) {					\
+		switch (sizeof(*(ptr))) {			\
+		case 2:						\
+			x = swab16(x);				\
+			break;					\
+		case 4:						\
+			x = swab32(x);				\
+			break;					\
+		case 8:						\
+			x = swab64(x);				\
+			break;					\
+		default:					\
+			break;					\
+		}						\
+	}							\
+	ret;							\
+})
+
+#define __vq_put_user(vq, x, ptr)					\
+({								\
+	__typeof__(*(ptr)) y = (x);				\
+	if (vq->byteswap) {					\
+		switch (sizeof(*(ptr))) {			\
+		case 2:						\
+			y = swab16(x);				\
+			break;					\
+		case 4:						\
+			y = swab32(x);				\
+			break;					\
+		case 8:						\
+			y = swab64(x);				\
+			break;					\
+		default:					\
+			break;					\
+		}						\
+	}							\
+	__put_user(y, ptr);					\
+})
+
+static void vring_desc_swap(struct vring_desc *desc)
+{
+	desc->addr  = swab64(desc->addr);
+	desc->len   = swab32(desc->len);
+	desc->flags = swab16(desc->flags);
+	desc->next  = swab16(desc->next);
+}
+
 static int vhost_update_used_flags(struct vhost_virtqueue *vq)
 {
 	void __user *used;
-- 
1.7.10.4

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