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cinit commands, Nico Schottelius 2005-04-28
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cinit allows communication through a socket (see ipc.thoughs for reasons).

Sockets allow to find out the accessing uid, gid and pid (uses SO_PEERCRED as
socketoption).

The communication-protocol is binary.

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Protocol overview
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Any communication begins with a command. A command is a one byte
unsigned char. Depending on the command, the communication has its own
semantics.


Commands are: (values can be found in cinit.h)

   CMD_START_SVC:    I want to start a service.
   CMD_CHG_STATUS:   I want to change the status of a service.
   CMD_STOP_SVC:     Please shutdown a service and its dependencies.
   CMD_KILL_SVC:     Shutdown a service, don't care about its dependencies.

   CMD_RESCUE:       Kill everything, and spawn a sulogin shell.
   CMD_INIT:         Start all services (again possibly).
   
   CMD_HALT:         Halt the system.
   CMD_REBOOT:       Reboot the system.
   CMD_POWEROFF:     Power-off the system.

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Detailled command-listing
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CMD_START_SVC
   1. int len;       /* length of service name, including \0 */
   2. char *svc;     /* name of the service, absolute pathname */ 

   cinit returns:
      a) ok, a SID, a service ID: int svc_id; [ really need int? ]
      b) fail, [currently only fail is returned]
         a) already running
         b) svc_name too long / not allowed

   [ A service identification is used for faster searching in cinit.
     It is also a hint for developers of external software, that they should not
     be able to use CMD_CHG_STATUS, if they didn't start a service.
     They should use CMD_STOP_SVC to stop a service.
     Starting a service is currently done via exec() in the external program or
     a cinit-fork(). ]

CMD_CHG_STATUS:   I want to change the status of a service.
   0. int svc_id;    /* service ID to change */
   1. char status;   /* status:
                        once: started successfully the service once.
                        fail: tried to start once, but the service exit uncgrafully
   UNUSED!              respawn: I am on it, as soon it exists I'll restart! */
   2. pid_t pid      /* the pid of the service, if started once
                        or the pid of the service watcher, if respawning */

   cinit returns: MSG_OK|MSG_FAIL (char)

CMD_STOP_SVC:     Please shutdown a service and its dependencies.
   1. int len;       /* length of service name, including \0 */
   2. char *svc;     /* name of the service, absolute pathname */ 

   cinit returns: ready...

CMD_KILL_SVC:     Shutdown a service, don't care about its dependencies.
   1. int len;       /* length of service name, including \0 */
   2. char *svc;     /* name of the service, absolute pathname */ 

   cinit returns: ready...

CMD_INIT:         Start all services (again possibly).
   cinit returns: ready...

CMD_RESCUE:       Kill everything, and spawn a sulogin shell.
CMD_HALT:         Halt the system.
CMD_REBOOT:       Reboot the system.
CMD_POWEROFF:     Power-off the system.