s6
Software
skarnet.org

The s6-fdholder-store program

s6-fdholder-store connects to a fd-holding daemon listening on a Unix domain socket, and gives it a copy of one of its open file descriptors for the daemon to hold.

Interface

     s6-fdholder-store [ -d fd ] [ -T fdtimeout ] [ -t timeout ] path id

• s6-fdholder-store executes into s6-ipcclient path s6-fdholder-storec id. It does nothing else: it is just a convenience program. The s6-ipcclient program connects to a Unix socket at path, and the s6-fdholder-storec program transmits the desired file descriptor over the socket.
• It should be used to connect to a s6-fdholderd daemon, which will store the file descriptor given by the user.

Options

• -d fd : store descriptor number fd. By default, fd is 0 (i.e. the program's stdin will be stored). s6-fdholder-store replaces its stdin with fd before executing into s6-ipcclient s6-fdholder-storec.
• -T fdtimeout : the descriptor is stored with an expiration time of fdtimeout milliseconds, which means the s6-fdholderd daemon will close and get rid of the descriptor after that time. By default, fdtimeout is 0, which means infinite - no expiration time.
• -t timeout : if the operation cannot be processed in timeout milliseconds, then fail with an error message. Communications with the server should be near-instant, so this option is only here to protect users against programming errors (connecting to the wrong socket, for instance).

Usage example

   s6-ipcserver-socketbinder /tmp/mysocket s6-fdholder-store /service/fdholderd/s MYSOCKET

will open a Unix domain socket, bind it to /tmp/mysocket and listen to incoming connections, then give it to a s6-fdholderd instance listening on /service/fdholderd/s, with no expiration date, with the "MYSOCKET" identifier. Another program will be able to retrieve the socket later, using s6-fdholder-retrieve.