> However 6 is probably too low - in nbdcopy we use 64.
I kept it low just to verify the system works in the way I intended it to.

> So you can
> open multiple TCP connections on each side and issue multiple
> commands in flight on each of those connections.
I will look into this, so we open multiple sockets hence get multiple socket_fds which we can read from and write to?

> The code looks very minimal at the moment. I'm not very familiar with
> the fmt:: class.
It's just for formatting and output like printf.

>Does it successfully make a handshake to ‘nbdkit -o’
> yet?

I read in the protocol document https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md#oldstyle-negotiation

that handshake is just about the server sending data to the client on accept,

I open a socket and connect then read the handshake, and with the data,

then populate NbdConnection variables. All this is done currently in the

constructor of NbdConnection synchronously. So I guess the answer

is yes.

Current data I receive after handshake from source and destination ports

Copying from port 1234 to port 2345.
┌──────────────────────────────┐
│ source │
└──────────────────────────────┘
NBDMAGIC (0x4e42444d41474943)
0x420281861253
4096
0b0000000000000000
0b0000110101101101
┌──────────────────────────────┐
│ destination │
└──────────────────────────────┘
NBDMAGIC (0x4e42444d41474943)
0x420281861253
8192
0b0000000000000000
0b0000110101101101

and then the program ends, destructors call disconnecting code.

command to run nbkit server

nbdkit data ' ( 0x55 0xAA )*2048 ' -o -f -p 1234

> I notice that although you create an io_uring you're not using it.
> But I guess that's still to come.

I am making it now done with the NBD read request submission

should be ready soon.

Thanks and regards,

Abhay