Il 12/03/2014 21:26, Michael S. Tsirkin ha scritto:
+Event queue:
+The only current event passed is a message to denote the host
+wants to update the layout of the screens. It contains the same
+info as the response to VIRTGPU_CMD_GET_DISPLAY_INFO.
I wonder if an event queue is the best mechanism if you can get the same
info from a command anyway. For virtio-scsi I used a queue because I
needed to specify which target or LUN the event applied to, but here you
do not need it and a queue is susceptible to dropped events.
Perhaps a configuration field is better, like this:
u32 events_read;
u32 events_clear;
A new event sets a bit in events_read and generates a configuration
change interrupt. The guest should never write to events_read.
Writing to events_clear has the side effect of the device doing
"events_read &= ~events_clear". We cannot have R/W1C fields in virtio,
but this approximation is good enough.
When the guest receives a configuration change interrupt, it reads
event_read. If it is nonzero, it writes the same value it read to
events_clear, and sends the necessary commands to the card in order to
retrieve the event data. It can then read again event_read, and loop if
it is again nonzero.
Paolo
