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vhost: Add high-level state save/load functions

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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>
This commit is contained in:
Hanna Czenczek 2023-10-16 15:42:42 +02:00 • committed by Michael S. Tsirkin
parent cda83adc62
commit 4a00d5d7f4
2 changed files with 239 additions and 0 deletions
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35
include/hw/virtio/vhost.h
View file

@ -429,4 +429,39 @@ 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