How does the SMB handshake work?

[JPT]

Hi,

I am currently implementing a SMB-Server using 
https://github.com/TalAloni/SMBLibrary

I am slowly getting to a working server.

But Samba client tries to negotiate the features and I just cannot find 
any information on what is going on.

samba sends:

INTFileStore.DeviceIOControl(handle=(null), 
ctlCode=0x140204(devicetype=14, accessmode=0, 
function=81),inputLength=28, maxOutputLength=24)

the input buffer contains:
FSCTL_VALIDATE_NEGOTIATE_INFO request parsed: StructSize=0, 
DialectCount=0, ClientSecMode=0xBE4D, ClientCaps=0x48F4C728,
ClientGuid=2a997584-1896-3636-0100-020002021002, Dialects=[]

How do I find out what this actually means?

The AI created an example output array, but it needs 28 bytes, while 
Samba only gives 24.
The AI says it's called SMB2_VALIDATE_NEGOTIATE_INFO_RESPONSE but I just 
cannot find anything on this name or how the output array should look like.

Samba does not increase the buffer size, instead it just tells
tree connect failed: NT_STATUS_BUFFER_TOO_SMALL

any help appreciated.

JPT