WebRTC streamer and vhost-user-input backend processes communicate with a client-server protocol - #3111
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The webRTC streamer can connect to a unix socket for each input device to inject input events and receive status feedback, in addition to the existing approach based on receiving the connection as an inherited file descriptor. The behavior is chosen base on command line flags passed by run_cvd. Bug: b/552079861
and implement it with the existing socket pair connected to stdin. Bug: b/552079861
The vhost-user-input process accepts a UNIX socket's fd via command line flag. When given, events are not read from stdin, but instead from clients connected to that unix socket. Multiple clients can connect at the same time and the server guarantees that each group of events ending in a SYN_REPORT event is delivered to the VMM atomically. Bug: b/552079861
webrtc connects to a unix socket hosted by vhu-input instead of through a socket pair inherited from run_cvd. run_cvd unconditionally enables this behavior, assuming that webRTC and cf_vhost_user_input are already substituted everywhere run_cvd is substituted. Bug: b/552079861
The frontend disconnects when crosvm restarts. If the restart was initiated by run_cvd, the event sources (webRTC) will reconnect to the corresponding server and everything works as intended. When the restart is started in the guest, for example with `adb reboot`, no reconnection occurs and input stopped working. By keeping the same event source for all frontend connections, the existing connections with webRTC are maintained. Bug: b/554190370
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cf_vhost_user_inputlistens on a UNIX socket server it inherits fromrun_cvd.webRTCconnects to this server to inject input events (mouse, touch, keyboard, etc) to the device backends. This enables the input backend to receive events from sources outside the streamer process.In addition to the protocol change, the device backend ensures all groups of events sent to the guest driver end in a
SYN_REPORT. TheseSYN_REPORTevents are used to group events from multiple sources so that the driver receives a valid flow of events.The behavior is enabled by run_cvd by the flags it launches
webRTCandcf_vhost_user_inputwith. When therun_cvdbinary is not substituted, events are sent via a socket pair as before. It would be a problem ifrun_cvdwas substituted butwebRTCorcf_vhost_user_inputwas not, but this situation is extremely unlikely since the latter have been substituted for a while now.Bug: b/552079861