Multiple smbd processes usually run simultaneously - a main daemon process and couple of connections processes. Samba code has special API that allows different processes send messages each other. There are two implementations of Messaging code - different in current Samba3 and Samba4 code.
Samba 3 implementation
This implementaion uses Tdb file for storing messages and UNIX signals for notifying message receiver.
All messages are stored in _messages.tdb_ file (one can find it in _var/locks_ directory). Each message is just a database record that has six fields:
- messaging version (there is only one version now - 1)
- message type
- sender process id
- receiver process id
- message data length
- message data
There are lot of message types in Samba3, you can see them all in _include/messages.h_ file.
Process sends a message to other process with special function message_send_pid and to all processes with message_send_all. Each process should call message_dispatch routinely to check if messages were received and run appropriate handler.
Samba 4 implementation
This implementation uses UNIX domain sockets.