tree 18464de6d930c25da86e3340afa458cd85519121
parent 513d95ef53569b2345e1e12337bade61f0cca2aa
author Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com> 1557444413 -0700
committer Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com> 1568312030 +0000

Add flow control to prevent buffer over run

This service uses direct frame update with bypassing image
compression and invalidating logic in libvncserver to achieve
better performance by using of H/W compressed JPEG frames as those
come from the video engine driver.

This behavior helps quick frame update using very small amount of
CPU resources but it causes a side effect which crashes bmcweb
by OOM killer due to a buffer over run issue. Usually, this issue
happens often in a slow speed connection because this service
keeps sending all frames without any handshaking with clients so
a session buffer in the bmcweb gets bigger and bigger since the
low speed connection can't send all stream data on time.

To fix this issue, this commit adds flow control logic to make
frame updating handshakes with client so that it'll send frames
only when it recieved client frame update messages. All other
frames when the client doesn't request will be dropped out to
prevent the buffer over run issue.

Tested:
bmcweb didn't keep increasing its KVM session buffer.
KVM worked well with showing good refresh speed.

resolves https://github.com/openbmc/bmcweb/issues/80

Change-Id: I6b09a711137d15a38fce59adada9bf3d00afde86
Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>