Hey Everyone!
I'm having trouble figuring out how the RPC mechanism works in Gluster.
Any help would be hugely appreciated!
When a client makes a request from the glusterd service an xdr encoded
rpc is sent to it. From what I'm gathering by looking at the source and
GDB the main struct to be concerned with is:
struct rpc_transport_req {
rpc_transport_msg_t msg;
rpc_transport_rsp_t rsp;
struct rpc_req *rpc_req;
};
From tracing it down to writev I see that the data looks as follows
before being written out:
(gdb) p req
$4 = {msg = {rpchdr = 0x7ffff36c7c00, rpchdrcount = 1, proghdr =
0x7ffff36c7d20,
proghdrcount = 1, progpayload = 0x0, progpayloadcount = 0, iobref =
0x7fffe4000920}, rsp = {
rsphdr = 0x0, rsphdr_count = 0, rsp_payload = 0x0,
rsp_payload_count = 0, rsp_iobref = 0x0},
rpc_req = 0x555555802dac}
I'm having trouble figuring out if this req variable is actually what is
being written out to the wire.
Now on the reply side the first header is the length of the reply. That
makes sense. What I'm not getting is if the rpc_transport_req is
actually being serialized with xdr or are parts of it being serialized?
It's hard to tell. I need to read the __socket_proto_state_machine over
again and understand it better. I searched around for notes or anything
online and there's really almost zero written about this.
So my questions are:
1. Is the rpc_transport_req being xdr encoded onto the wire?
2. Are there any good materials out there that explain the protocol?
Figuring it out by reading the source and break pointing the code is
slow going. Esp with the epoll threads making tracking things down hard.
Thanks for the help!
-Chris
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