On 13/03/2023 19:48, Hanna Czenczek wrote:
Add a virtio-fs-specific vhost-user interface to facilitate migrating
back-end-internal state. We plan to migrate the internal state simply
as a binary blob after the streaming phase, so all we need is a way to
transfer such a blob from and to the back-end. We do so by using a
dedicated area of shared memory through which the blob is transferred in
chunks.
This patch adds the following vhost operations (and implements them for
vhost-user):
- FS_SET_STATE_FD: The front-end passes a dedicated shared memory area
to the back-end. This area will be used to transfer state via the
other two operations.
(After the transfer FS_SET_STATE_FD detaches the shared memory area
again.)
- FS_GET_STATE: The front-end asks the back-end to place a chunk of
internal state into the shared memory area.
- FS_SET_STATE: The front-end puts a chunk of internal state into the
shared memory area, and asks the back-end to fetch it.
On the source side, the back-end is expected to serialize its internal
state either when FS_SET_STATE_FD is invoked, or when FS_GET_STATE is
invoked the first time. On subsequent FS_GET_STATE calls, it memcpy()s
parts of that serialized state into the shared memory area.
On the destination side, the back-end is expected to collect the state
blob over all FS_SET_STATE calls, and then deserialize and apply it once
FS_SET_STATE_FD detaches the shared memory area.
Signed-off-by: Hanna Czenczek <hre...@redhat.com>
---
include/hw/virtio/vhost-backend.h | 9 ++
include/hw/virtio/vhost.h | 68 +++++++++++++++
hw/virtio/vhost-user.c | 138 ++++++++++++++++++++++++++++++
hw/virtio/vhost.c | 29 +++++++
4 files changed, 244 insertions(+)
diff --git a/include/hw/virtio/vhost-backend.h
b/include/hw/virtio/vhost-backend.h
index ec3fbae58d..fa3bd19386 100644
--- a/include/hw/virtio/vhost-backend.h
+++ b/include/hw/virtio/vhost-backend.h
@@ -42,6 +42,12 @@ typedef int (*vhost_backend_init)(struct vhost_dev *dev,
void *opaque,
typedef int (*vhost_backend_cleanup)(struct vhost_dev *dev);
typedef int (*vhost_backend_memslots_limit)(struct vhost_dev *dev);
+typedef ssize_t (*vhost_fs_get_state_op)(struct vhost_dev *dev,
+ uint64_t state_offset, size_t size);
+typedef int (*vhost_fs_set_state_op)(struct vhost_dev *dev,
+ uint64_t state_offset, size_t size);
+typedef int (*vhost_fs_set_state_fd_op)(struct vhost_dev *dev, int memfd,
+ size_t size);
typedef int (*vhost_net_set_backend_op)(struct vhost_dev *dev,
struct vhost_vring_file *file);
typedef int (*vhost_net_set_mtu_op)(struct vhost_dev *dev, uint16_t mtu);
@@ -138,6 +144,9 @@ typedef struct VhostOps {
vhost_backend_init vhost_backend_init;
vhost_backend_cleanup vhost_backend_cleanup;
vhost_backend_memslots_limit vhost_backend_memslots_limit;
+ vhost_fs_get_state_op vhost_fs_get_state;
+ vhost_fs_set_state_op vhost_fs_set_state;
+ vhost_fs_set_state_fd_op vhost_fs_set_state_fd;
vhost_net_set_backend_op vhost_net_set_backend;
vhost_net_set_mtu_op vhost_net_set_mtu;
vhost_scsi_set_endpoint_op vhost_scsi_set_endpoint;
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index a52f273347..b1ad9785dd 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -336,4 +336,72 @@ int vhost_dev_set_inflight(struct vhost_dev *dev,
struct vhost_inflight *inflight);
int vhost_dev_get_inflight(struct vhost_dev *dev, uint16_t queue_size,
struct vhost_inflight *inflight);
+
+/**
+ * vhost_fs_set_state_fd(): Share memory with a virtio-fs vhost
+ * back-end for transferring internal state for the purpose of
+ * migration. Calling this function again will have the back-end
+ * unregister (free) the previously shared memory area.
+ *
+ * @dev: The vhost device
+ * @memfd: File descriptor associated with the shared memory to share.
+ * If negative, no memory area is shared, only releasing the
+ * previously shared area, and announcing the end of transfer
+ * (which, on the destination side, should lead to the
+ * back-end deserializing and applying the received state).
+ * @size: Size of the shared memory area
+ *
+ * Returns 0 on success, and -errno on failure.
+ */
+int vhost_fs_set_state_fd(struct vhost_dev *dev, int memfd, size_t size);
+
+/**
+ * vhost_fs_get_state(): Request the virtio-fs vhost back-end to place
+ * a chunk of migration state into the shared memory area negotiated
+ * through vhost_fs_set_state_fd(). May only be used for migration,
+ * and only by the source side.
+ *
+ * The back-end-internal migration state is treated as a binary blob,
+ * which is transferred in chunks to fit into the shared memory area.
+ *
+ * @dev: The vhost device
+ * @state_offset: Offset into the state blob of the first byte to be
+ * transferred
+ * @size: Number of bytes to transfer at most; must not exceed the
+ * size of the shared memory area
+ *
+ * On success, returns the number of bytes that remain in the full
+ * state blob from the beginning of this chunk (i.e. the full size of
+ * the blob, minus @state_offset). When transferring the final chunk,
+ * this may be less than @size. The shared memory will contain the
+ * requested data, starting at offset 0 into the SHM, and counting
+ * `MIN(@size, returned value)` bytes.
+ *
+ * On failure, returns -errno.
+ */
+ssize_t vhost_fs_get_state(struct vhost_dev *dev, uint64_t state_offset,
+ uint64_t size);
+
+/**
+ * vhost_fs_set_state(): Request the virtio-fs vhost back-end to fetch
+ * a chunk of migration state from the shared memory area negotiated
+ * through vhost_fs_set_state_fd(). May only be used for migration,
+ * and only by the destination side.
+ *
+ * The back-end-internal migration state is treated as a binary blob,
+ * which is transferred in chunks to fit into the shared memory area.
+ *
+ * The front-end (i.e. the caller) must transfer the whole state to
+ * the back-end, without holes.
+ *
+ * @vdev: the VirtIODevice structure
+ * @state_offset: Offset into the state blob of the first byte to be
+ * transferred
+ * @size: Length of the chunk to transfer; must not exceed the size of
+ * the shared memory area
+ *
+ * Returns 0 on success, and -errno on failure.
+ */
+int vhost_fs_set_state(struct vhost_dev *dev, uint64_t state_offset,
+ uint64_t size);
#endif
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index e5285df4ba..7fd1fb1ed3 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -130,6 +130,9 @@ typedef enum VhostUserRequest {
VHOST_USER_REM_MEM_REG = 38,
VHOST_USER_SET_STATUS = 39,
VHOST_USER_GET_STATUS = 40,
+ VHOST_USER_FS_SET_STATE_FD = 41,
+ VHOST_USER_FS_GET_STATE = 42,
+ VHOST_USER_FS_SET_STATE = 43,
VHOST_USER_MAX
} VhostUserRequest;
@@ -210,6 +213,15 @@ typedef struct {
uint32_t size; /* the following payload size */
} QEMU_PACKED VhostUserHeader;
+/*
+ * Request and reply payloads of VHOST_USER_FS_GET_STATE, and request
+ * payload of VHOST_USER_FS_SET_STATE.
+ */
+typedef struct VhostUserFsState {
+ uint64_t state_offset;
+ uint64_t size;
+} VhostUserFsState;
+
typedef union {
#define VHOST_USER_VRING_IDX_MASK (0xff)
#define VHOST_USER_VRING_NOFD_MASK (0x1 << 8)
@@ -224,6 +236,7 @@ typedef union {
VhostUserCryptoSession session;
VhostUserVringArea area;
VhostUserInflight inflight;
+ VhostUserFsState fs_state;
} VhostUserPayload;
typedef struct VhostUserMsg {
@@ -2240,6 +2253,128 @@ static int vhost_user_net_set_mtu(struct vhost_dev
*dev, uint16_t mtu)
return 0;
}
+static int vhost_user_fs_set_state_fd(struct vhost_dev *dev, int memfd,
+ size_t size)
+{
+ int ret;
+ bool reply_supported = virtio_has_feature(dev->protocol_features,
+ VHOST_USER_PROTOCOL_F_REPLY_ACK);
+ VhostUserMsg msg = {
+ .hdr = {
+ .request = VHOST_USER_FS_SET_STATE_FD,
+ .flags = VHOST_USER_VERSION,
+ .size = sizeof(msg.payload.u64),
+ },
+ .payload.u64 = size,
+ };
+
+ if (reply_supported) {
+ msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
+ }
+
+ if (memfd < 0) {
+ assert(size == 0);
+ ret = vhost_user_write(dev, &msg, NULL, 0);
+ } else {
+ ret = vhost_user_write(dev, &msg, &memfd, 1);
+ }
+ if (ret < 0) {
+ return ret;
+ }
+
+ if (reply_supported) {
+ return process_message_reply(dev, &msg);
+ }
+
+ return 0;
+}
+
+static ssize_t vhost_user_fs_get_state(struct vhost_dev *dev,
+ uint64_t state_offset,
+ size_t size)
+{
Am I right to assume that vrings are supposed to be stopped to get/set
state?
If I am shouldn't we check it before sending message or do you believe it is
better to return error from backend in these cases?
+ int ret;
+ VhostUserMsg msg = {
+ .hdr = {
+ .request = VHOST_USER_FS_GET_STATE,
+ .flags = VHOST_USER_VERSION,
+ .size = sizeof(msg.payload.fs_state),
+ },
+ .payload.fs_state = {
+ .state_offset = state_offset,
+ .size = size,
+ },
+ };
+
+ ret = vhost_user_write(dev, &msg, NULL, 0);
+ if (ret < 0) {
+ return ret;
+ }
+
+ ret = vhost_user_read(dev, &msg);
+ if (ret < 0) {
+ return ret;
+ }
+
+ if (msg.hdr.request != VHOST_USER_FS_GET_STATE) {
+ error_report("Received unexpected message type: "
+ "Expected %d, received %d",
+ VHOST_USER_FS_GET_STATE, msg.hdr.request);
+ return -EPROTO;
+ }
+
+ if (msg.hdr.size != sizeof(VhostUserFsState)) {
+ error_report("Received unexpected message length: "
+ "Expected %" PRIu32 ", received %zu",
+ msg.hdr.size, sizeof(VhostUserFsState));
+ return -EPROTO;
+ }
+
+ if (msg.payload.fs_state.size > SSIZE_MAX) {
+ error_report("Remaining state size returned by back end is too high: "
+ "Expected up to %zd, reported %" PRIu64,
+ SSIZE_MAX, msg.payload.fs_state.size);
+ return -EPROTO;
+ }
+
+ return msg.payload.fs_state.size;
+}
+
+static int vhost_user_fs_set_state(struct vhost_dev *dev,
+ uint64_t state_offset,
+ size_t size)
+{
+ int ret;
+ bool reply_supported = virtio_has_feature(dev->protocol_features,
+ VHOST_USER_PROTOCOL_F_REPLY_ACK);
+ VhostUserMsg msg = {
+ .hdr = {
+ .request = VHOST_USER_FS_SET_STATE,
+ .flags = VHOST_USER_VERSION,
+ .size = sizeof(msg.payload.fs_state),
+ },
+ .payload.fs_state = {
+ .state_offset = state_offset,
+ .size = size,
+ },
+ };
+
+ if (reply_supported) {
+ msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
+ }
+
+ ret = vhost_user_write(dev, &msg, NULL, 0);
+ if (ret < 0) {
+ return ret;
+ }
+
+ if (reply_supported) {
+ return process_message_reply(dev, &msg);
+ }
+
+ return 0;
+}
+
static int vhost_user_send_device_iotlb_msg(struct vhost_dev *dev,
struct vhost_iotlb_msg *imsg)
{
@@ -2716,4 +2851,7 @@ const VhostOps user_ops = {
.vhost_get_inflight_fd = vhost_user_get_inflight_fd,
.vhost_set_inflight_fd = vhost_user_set_inflight_fd,
.vhost_dev_start = vhost_user_dev_start,
+ .vhost_fs_set_state_fd = vhost_user_fs_set_state_fd,
+ .vhost_fs_get_state = vhost_user_fs_get_state,
+ .vhost_fs_set_state = vhost_user_fs_set_state,
};
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index a266396576..ef8252c90e 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -2075,3 +2075,32 @@ int vhost_net_set_backend(struct vhost_dev *hdev,
return -ENOSYS;
}
+
+int vhost_fs_set_state_fd(struct vhost_dev *dev, int memfd, size_t size)
+{
+ if (dev->vhost_ops->vhost_fs_set_state_fd) {
+ return dev->vhost_ops->vhost_fs_set_state_fd(dev, memfd, size);
+ }
+
+ return -ENOSYS;
+}
+
+ssize_t vhost_fs_get_state(struct vhost_dev *dev, uint64_t state_offset,
+ uint64_t size)
+{
+ if (dev->vhost_ops->vhost_fs_get_state) {
+ return dev->vhost_ops->vhost_fs_get_state(dev, state_offset, size);
+ }
+
+ return -ENOSYS;
+}
+
+int vhost_fs_set_state(struct vhost_dev *dev, uint64_t state_offset,
+ uint64_t size)
+{
+ if (dev->vhost_ops->vhost_fs_set_state) {
+ return dev->vhost_ops->vhost_fs_set_state(dev, state_offset, size);
+ }
+
+ return -ENOSYS;
+}
