On Wed, 25 Oct 2023 11:49:19 +0200, Matias Ezequiel Vara Larsen wrote: > > This commit uses the ack() callback to determine when a buffer has been > updated, then exposes it to guest. > > The current mechanism splits a dma buffer into descriptors that are > exposed to the device. This dma buffer is shared with the user > application. When the device consumes a buffer, the driver moves the > request from the used ring to available ring. > > The driver exposes the buffer to the device without knowing if the > content has been updated from the user. The section 2.8.21.1 of the > virtio spec states that: "The device MAY access the descriptor chains > the driver created and the memory they refer to immediately". If the > device picks up buffers from the available ring just after it is > notified, it happens that the content may be old. > > When the ack() callback is invoked, the driver exposes only the buffers > that have already been updated, i.e., enqueued in the available ring. > Thus, the device always picks up a buffer that is updated. > > For capturing, the driver starts by exposing all the available buffers > to device. After device updates the content of a buffer, it enqueues it > in the used ring. It is only after the ack() for capturing is issued > that the driver re-enqueues the buffer in the available ring. > > Co-developed-by: Anton Yakovlev <anton.yakovlev@xxxxxxxxxxxxxxx> > Signed-off-by: Anton Yakovlev <anton.yakovlev@xxxxxxxxxxxxxxx> > Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@xxxxxxxxxx> Applied now to for-next branch. thanks, Takashi
