vhost: Add high-level state save/load functions
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. Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Hanna Czenczek <hreitz@redhat.com> Message-Id: <20231016134243.68248-7-hreitz@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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@ -2196,3 +2196,207 @@ int vhost_check_device_state(struct vhost_dev *dev, Error **errp)
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"vhost transport does not support migration state transfer");
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"vhost transport does not support migration state transfer");
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return -ENOSYS;
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return -ENOSYS;
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}
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}
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int vhost_save_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp)
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{
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/* Maximum chunk size in which to transfer the state */
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const size_t chunk_size = 1 * 1024 * 1024;
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g_autofree void *transfer_buf = NULL;
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g_autoptr(GError) g_err = NULL;
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int pipe_fds[2], read_fd = -1, write_fd = -1, reply_fd = -1;
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int ret;
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/* [0] for reading (our end), [1] for writing (back-end's end) */
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if (!g_unix_open_pipe(pipe_fds, FD_CLOEXEC, &g_err)) {
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error_setg(errp, "Failed to set up state transfer pipe: %s",
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g_err->message);
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ret = -EINVAL;
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goto fail;
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}
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read_fd = pipe_fds[0];
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write_fd = pipe_fds[1];
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/*
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* VHOST_TRANSFER_STATE_PHASE_STOPPED means the device must be stopped.
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* Ideally, it is suspended, but SUSPEND/RESUME currently do not exist for
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* vhost-user, so just check that it is stopped at all.
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*/
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assert(!dev->started);
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/* Transfer ownership of write_fd to the back-end */
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ret = vhost_set_device_state_fd(dev,
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VHOST_TRANSFER_STATE_DIRECTION_SAVE,
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VHOST_TRANSFER_STATE_PHASE_STOPPED,
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write_fd,
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&reply_fd,
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errp);
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if (ret < 0) {
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error_prepend(errp, "Failed to initiate state transfer: ");
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goto fail;
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}
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/* If the back-end wishes to use a different pipe, switch over */
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if (reply_fd >= 0) {
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close(read_fd);
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read_fd = reply_fd;
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}
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transfer_buf = g_malloc(chunk_size);
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while (true) {
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ssize_t read_ret;
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read_ret = RETRY_ON_EINTR(read(read_fd, transfer_buf, chunk_size));
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if (read_ret < 0) {
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ret = -errno;
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error_setg_errno(errp, -ret, "Failed to receive state");
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goto fail;
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}
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assert(read_ret <= chunk_size);
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qemu_put_be32(f, read_ret);
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if (read_ret == 0) {
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/* EOF */
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break;
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}
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qemu_put_buffer(f, transfer_buf, read_ret);
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}
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/*
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* Back-end will not really care, but be clean and close our end of the pipe
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* before inquiring the back-end about whether transfer was successful
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*/
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close(read_fd);
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read_fd = -1;
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/* Also, verify that the device is still stopped */
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assert(!dev->started);
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ret = vhost_check_device_state(dev, errp);
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if (ret < 0) {
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goto fail;
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}
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ret = 0;
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fail:
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if (read_fd >= 0) {
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close(read_fd);
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}
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return ret;
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}
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int vhost_load_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp)
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{
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size_t transfer_buf_size = 0;
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g_autofree void *transfer_buf = NULL;
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g_autoptr(GError) g_err = NULL;
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int pipe_fds[2], read_fd = -1, write_fd = -1, reply_fd = -1;
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int ret;
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/* [0] for reading (back-end's end), [1] for writing (our end) */
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if (!g_unix_open_pipe(pipe_fds, FD_CLOEXEC, &g_err)) {
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error_setg(errp, "Failed to set up state transfer pipe: %s",
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g_err->message);
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ret = -EINVAL;
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goto fail;
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}
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read_fd = pipe_fds[0];
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write_fd = pipe_fds[1];
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/*
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* VHOST_TRANSFER_STATE_PHASE_STOPPED means the device must be stopped.
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* Ideally, it is suspended, but SUSPEND/RESUME currently do not exist for
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* vhost-user, so just check that it is stopped at all.
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*/
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assert(!dev->started);
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/* Transfer ownership of read_fd to the back-end */
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ret = vhost_set_device_state_fd(dev,
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VHOST_TRANSFER_STATE_DIRECTION_LOAD,
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VHOST_TRANSFER_STATE_PHASE_STOPPED,
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read_fd,
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&reply_fd,
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errp);
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if (ret < 0) {
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error_prepend(errp, "Failed to initiate state transfer: ");
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goto fail;
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}
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/* If the back-end wishes to use a different pipe, switch over */
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if (reply_fd >= 0) {
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close(write_fd);
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write_fd = reply_fd;
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}
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while (true) {
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size_t this_chunk_size = qemu_get_be32(f);
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ssize_t write_ret;
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const uint8_t *transfer_pointer;
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if (this_chunk_size == 0) {
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/* End of state */
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break;
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}
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if (transfer_buf_size < this_chunk_size) {
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transfer_buf = g_realloc(transfer_buf, this_chunk_size);
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transfer_buf_size = this_chunk_size;
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}
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if (qemu_get_buffer(f, transfer_buf, this_chunk_size) <
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this_chunk_size)
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{
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error_setg(errp, "Failed to read state");
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ret = -EINVAL;
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goto fail;
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}
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transfer_pointer = transfer_buf;
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while (this_chunk_size > 0) {
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write_ret = RETRY_ON_EINTR(
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write(write_fd, transfer_pointer, this_chunk_size)
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);
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if (write_ret < 0) {
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ret = -errno;
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error_setg_errno(errp, -ret, "Failed to send state");
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goto fail;
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} else if (write_ret == 0) {
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error_setg(errp, "Failed to send state: Connection is closed");
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ret = -ECONNRESET;
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goto fail;
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}
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assert(write_ret <= this_chunk_size);
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this_chunk_size -= write_ret;
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transfer_pointer += write_ret;
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}
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}
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/*
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* Close our end, thus ending transfer, before inquiring the back-end about
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* whether transfer was successful
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*/
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close(write_fd);
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write_fd = -1;
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/* Also, verify that the device is still stopped */
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assert(!dev->started);
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ret = vhost_check_device_state(dev, errp);
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if (ret < 0) {
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goto fail;
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}
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ret = 0;
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fail:
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if (write_fd >= 0) {
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close(write_fd);
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}
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return ret;
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}
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@ -429,4 +429,39 @@ int vhost_set_device_state_fd(struct vhost_dev *dev,
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*/
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*/
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int vhost_check_device_state(struct vhost_dev *dev, Error **errp);
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int vhost_check_device_state(struct vhost_dev *dev, Error **errp);
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/**
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* vhost_save_backend_state(): High-level function to receive a vhost
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* back-end's state, and save it in @f. Uses
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* `vhost_set_device_state_fd()` to get the data from the back-end, and
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* stores it in consecutive chunks that are each prefixed by their
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* respective length (be32). The end is marked by a 0-length chunk.
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*
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* Must only be called while the device and all its vrings are stopped
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* (`VHOST_TRANSFER_STATE_PHASE_STOPPED`).
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*
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* @dev: The vhost device from which to save the state
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* @f: Migration stream in which to save the state
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* @errp: Potential error message
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*
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* Returns 0 on success, and -errno otherwise.
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*/
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int vhost_save_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp);
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/**
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* vhost_load_backend_state(): High-level function to load a vhost
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* back-end's state from @f, and send it over to the back-end. Reads
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* the data from @f in the format used by `vhost_save_state()`, and uses
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* `vhost_set_device_state_fd()` to transfer it to the back-end.
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*
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* Must only be called while the device and all its vrings are stopped
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* (`VHOST_TRANSFER_STATE_PHASE_STOPPED`).
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*
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* @dev: The vhost device to which to send the sate
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* @f: Migration stream from which to load the state
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* @errp: Potential error message
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*
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* Returns 0 on success, and -errno otherwise.
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*/
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int vhost_load_backend_state(struct vhost_dev *dev, QEMUFile *f, Error **errp);
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#endif
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#endif
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