vhost: switch to use new message format

We use to have message like: struct vhost_msg { int type; union { struct vhost_iotlb_msg iotlb; __u8 padding[64]; }; }; Unfortunately, there will be a hole of 32bit in 64bit machine because of the alignment. This leads a different formats between 32bit API and 64bit API. What's more it will break 32bit program running on 64bit machine. So fixing this by introducing a new message type with an explicit 32bit reserved field after type like: struct vhost_msg_v2 { __u32 type; __u32 reserved; union { struct vhost_iotlb_msg iotlb; __u8 padding[64]; }; }; We will have a consistent ABI after switching to use this. To enable this capability, introduce a new ioctl (VHOST_SET_BAKCEND_FEATURE) for userspace to enable this feature (VHOST_BACKEND_F_IOTLB_V2).

Jason Wang committed 8 years ago

Commit 429711a1 parent 9c2e9554 files · +111 −19Browse files

Showing the changes to include/uapi/linux (1 of 4 files). Show all

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include/uapi/linux/vhost.h+18−0

@@ -65,6 +65,7 @@ struct vhost_iotlb_msg { · 64 unmodified lines
65	65	};
66	66
67	67	#define VHOST_IOTLB_MSG 0x1
	68	+#define VHOST_IOTLB_MSG_V2 0x2
68	69
69	70	struct vhost_msg {
70	71	int type;
@@ -74,6 +75,15 @@ struct vhost_msg { · 3 unmodified lines
74	75	};
75	76	};
76	77
	78	+struct vhost_msg_v2 {
	79	+ __u32 type;
	80	+ __u32 reserved;
	81	+ union {
	82	+ struct vhost_iotlb_msg iotlb;
	83	+ __u8 padding[64];
	84	+ };
	85	+};
	86	+
77	87	struct vhost_memory_region {
78	88	__u64 guest_phys_addr;
79	89	__u64 memory_size; /* bytes */
@@ -160,6 +170,14 @@ struct vhost_memory { · 80 unmodified lines
160	170	#define VHOST_GET_VRING_BUSYLOOP_TIMEOUT _IOW(VHOST_VIRTIO, 0x24, \
161	171	struct vhost_vring_state)
162	172
	173	+/* Set or get vhost backend capability */
	174	+
	175	+/* Use message type V2 */
	176	+#define VHOST_BACKEND_F_IOTLB_MSG_V2 0x1
	177	+
	178	+#define VHOST_SET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x25, __u64)
	179	+#define VHOST_GET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x26, __u64)
	180	+
163	181	/* VHOST_NET specific defines */
164	182
165	183	/* Attach virtio net ring to a raw socket, or tap device.