@@ -417,4 +417,39 @@ int vhost_set_device_state_fd(struct vhost_dev *dev,
*/
int vhost_check_device_state(struct vhost_dev *dev, Error **errp);
+/**
+ * vhost_save_backend_state(): High-level function to receive a vhost
+ * back-end's state, and save it in @f. Uses
+ * `vhost_set_device_state_fd()` to get the data from the back-end, and
+ * stores it in consecutive chunks that are each prefixed by their
+ * respective length (be32). The end is marked by a 0-length chunk.
+ *
+ * Must only be called while the device and all its vrings are stopped
+ * (`VHOST_TRANSFER_STATE_PHASE_STOPPED`).
+ *
+ * @dev: The vhost device from which to save the state
+ * @f: Migration stream in which to save the state
+ * @errp: Potential error message
+ *
+ * Returns 0 on success, and -errno otherwise.
+ */
+int vhost_save_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp);
+
+/**
+ * vhost_load_backend_state(): High-level function to load a vhost
+ * back-end's state from @f, and send it over to the back-end. Reads
+ * the data from @f in the format used by `vhost_save_state()`, and uses
+ * `vhost_set_device_state_fd()` to transfer it to the back-end.
+ *
+ * Must only be called while the device and all its vrings are stopped
+ * (`VHOST_TRANSFER_STATE_PHASE_STOPPED`).
+ *
+ * @dev: The vhost device to which to send the sate
+ * @f: Migration stream from which to load the state
+ * @errp: Potential error message
+ *
+ * Returns 0 on success, and -errno otherwise.
+ */
+int vhost_load_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp);
+
#endif
@@ -2124,3 +2124,207 @@ int vhost_check_device_state(struct vhost_dev *dev, Error **errp)
"vhost transport does not support migration state transfer");
return -ENOSYS;
}
+
+int vhost_save_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp)
+{
+ /* Maximum chunk size in which to transfer the state */
+ const size_t chunk_size = 1 * 1024 * 1024;
+ g_autofree void *transfer_buf = NULL;
+ g_autoptr(GError) g_err = NULL;
+ int pipe_fds[2], read_fd = -1, write_fd = -1, reply_fd = -1;
+ int ret;
+
+ /* [0] for reading (our end), [1] for writing (back-end's end) */
+ if (!g_unix_open_pipe(pipe_fds, FD_CLOEXEC, &g_err)) {
+ error_setg(errp, "Failed to set up state transfer pipe: %s",
+ g_err->message);
+ ret = -EINVAL;
+ goto fail;
+ }
+
+ read_fd = pipe_fds[0];
+ write_fd = pipe_fds[1];
+
+ /*
+ * VHOST_TRANSFER_STATE_PHASE_STOPPED means the device must be stopped.
+ * Ideally, it is suspended, but SUSPEND/RESUME currently do not exist for
+ * vhost-user, so just check that it is stopped at all.
+ */
+ assert(!dev->started);
+
+ /* Transfer ownership of write_fd to the back-end */
+ ret = vhost_set_device_state_fd(dev,
+ VHOST_TRANSFER_STATE_DIRECTION_SAVE,
+ VHOST_TRANSFER_STATE_PHASE_STOPPED,
+ write_fd,
+ &reply_fd,
+ errp);
+ if (ret < 0) {
+ error_prepend(errp, "Failed to initiate state transfer: ");
+ goto fail;
+ }
+
+ /* If the back-end wishes to use a different pipe, switch over */
+ if (reply_fd >= 0) {
+ close(read_fd);
+ read_fd = reply_fd;
+ }
+
+ transfer_buf = g_malloc(chunk_size);
+
+ while (true) {
+ ssize_t read_ret;
+
+ read_ret = RETRY_ON_EINTR(read(read_fd, transfer_buf, chunk_size));
+ if (read_ret < 0) {
+ ret = -errno;
+ error_setg_errno(errp, -ret, "Failed to receive state");
+ goto fail;
+ }
+
+ assert(read_ret <= chunk_size);
+ qemu_put_be32(f, read_ret);
+
+ if (read_ret == 0) {
+ /* EOF */
+ break;
+ }
+
+ qemu_put_buffer(f, transfer_buf, read_ret);
+ }
+
+ /*
+ * Back-end will not really care, but be clean and close our end of the pipe
+ * before inquiring the back-end about whether transfer was successful
+ */
+ close(read_fd);
+ read_fd = -1;
+
+ /* Also, verify that the device is still stopped */
+ assert(!dev->started);
+
+ ret = vhost_check_device_state(dev, errp);
+ if (ret < 0) {
+ goto fail;
+ }
+
+ ret = 0;
+fail:
+ if (read_fd >= 0) {
+ close(read_fd);
+ }
+
+ return ret;
+}
+
+int vhost_load_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp)
+{
+ size_t transfer_buf_size = 0;
+ g_autofree void *transfer_buf = NULL;
+ g_autoptr(GError) g_err = NULL;
+ int pipe_fds[2], read_fd = -1, write_fd = -1, reply_fd = -1;
+ int ret;
+
+ /* [0] for reading (back-end's end), [1] for writing (our end) */
+ if (!g_unix_open_pipe(pipe_fds, FD_CLOEXEC, &g_err)) {
+ error_setg(errp, "Failed to set up state transfer pipe: %s",
+ g_err->message);
+ ret = -EINVAL;
+ goto fail;
+ }
+
+ read_fd = pipe_fds[0];
+ write_fd = pipe_fds[1];
+
+ /*
+ * VHOST_TRANSFER_STATE_PHASE_STOPPED means the device must be stopped.
+ * Ideally, it is suspended, but SUSPEND/RESUME currently do not exist for
+ * vhost-user, so just check that it is stopped at all.
+ */
+ assert(!dev->started);
+
+ /* Transfer ownership of read_fd to the back-end */
+ ret = vhost_set_device_state_fd(dev,
+ VHOST_TRANSFER_STATE_DIRECTION_LOAD,
+ VHOST_TRANSFER_STATE_PHASE_STOPPED,
+ read_fd,
+ &reply_fd,
+ errp);
+ if (ret < 0) {
+ error_prepend(errp, "Failed to initiate state transfer: ");
+ goto fail;
+ }
+
+ /* If the back-end wishes to use a different pipe, switch over */
+ if (reply_fd >= 0) {
+ close(write_fd);
+ write_fd = reply_fd;
+ }
+
+ while (true) {
+ size_t this_chunk_size = qemu_get_be32(f);
+ ssize_t write_ret;
+ const uint8_t *transfer_pointer;
+
+ if (this_chunk_size == 0) {
+ /* End of state */
+ break;
+ }
+
+ if (transfer_buf_size < this_chunk_size) {
+ transfer_buf = g_realloc(transfer_buf, this_chunk_size);
+ transfer_buf_size = this_chunk_size;
+ }
+
+ if (qemu_get_buffer(f, transfer_buf, this_chunk_size) <
+ this_chunk_size)
+ {
+ error_setg(errp, "Failed to read state");
+ ret = -EINVAL;
+ goto fail;
+ }
+
+ transfer_pointer = transfer_buf;
+ while (this_chunk_size > 0) {
+ write_ret = RETRY_ON_EINTR(
+ write(write_fd, transfer_pointer, this_chunk_size)
+ );
+ if (write_ret < 0) {
+ ret = -errno;
+ error_setg_errno(errp, -ret, "Failed to send state");
+ goto fail;
+ } else if (write_ret == 0) {
+ error_setg(errp, "Failed to send state: Connection is closed");
+ ret = -ECONNRESET;
+ goto fail;
+ }
+
+ assert(write_ret <= this_chunk_size);
+ this_chunk_size -= write_ret;
+ transfer_pointer += write_ret;
+ }
+ }
+
+ /*
+ * Close our end, thus ending transfer, before inquiring the back-end about
+ * whether transfer was successful
+ */
+ close(write_fd);
+ write_fd = -1;
+
+ /* Also, verify that the device is still stopped */
+ assert(!dev->started);
+
+ ret = vhost_check_device_state(dev, errp);
+ if (ret < 0) {
+ goto fail;
+ }
+
+ ret = 0;
+fail:
+ if (write_fd >= 0) {
+ close(write_fd);
+ }
+
+ return ret;
+}
vhost_save_backend_state() and vhost_load_backend_state() can be used by vhost front-ends to easily save and load the back-end's state to/from the migration stream. Because we do not know the full state size ahead of time, vhost_save_backend_state() simply reads the data in 1 MB chunks, and writes each chunk consecutively into the migration stream, prefixed by its length. EOF is indicated by a 0-length chunk. Signed-off-by: Hanna Czenczek <hreitz@redhat.com> --- include/hw/virtio/vhost.h | 35 +++++++ hw/virtio/vhost.c | 204 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 239 insertions(+)