If client stream does not have any data to sink and neither received
EOF, a dummy packet is sent to the daemon signalising client is ready to
sink some data. However, after we added event loop to client a race may
occur:
Thread 1 calls virNetClientStreamRecvPacket and since no data are cached
nor stream has EOF, it decides to send dummy packet to server which will
sent some data in turn. However, during this decision and actual message
exchange with server -
Thread 2 receives last stream data from server. Therefore an EOF is set
on stream and if there is a call waiting (which is not yet) it is woken
up. However, Thread 1 haven't sent anything so far, so there is no call
to be woken up. So this thread sent dummy packet to daemon, which
ignores that as no stream is associated with such packet and therefore
no reply will ever come.
This race causes client to hang indefinitely.
To facilitate creation of new clients using XDR RPC services,
pull alot of the remote driver code into a set of reusable
objects.
- virNetClient: Encapsulates a socket connection to a
remote RPC server. Handles all the network I/O for
reading/writing RPC messages. Delegates RPC encoding
and decoding to the registered programs
- virNetClientProgram: Handles processing and dispatch
of RPC messages for a single RPC (program,version).
A program can register to receive async events
from a client
- virNetClientStream: Handles generic I/O stream
integration to RPC layer
Each new client program now merely needs to define the list of
RPC procedures & events it wants and their handlers. It does
not need to deal with any of the network I/O functionality at
all.
