import cinit from unix.schottelius.org
Signed-off-by: Nico Schottelius <nico@ikn.schottelius.org>
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Nico Schottelius
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cinit - communication
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=====================
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Nico Schottelius <nico-linux-cinit__@__schottelius.org>
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0.1 for cinit-0.3, Initial version: 2006-08-11
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:Author Initials: NS
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This document describes the internal communication of cinit.
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It is thought to be read by developers.
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Introduction
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------------
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This document describes the messages used between cinit, cinit forks
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and other programs that want to talk to cinit. It does NOT
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describe the communication method, but only the messages sent
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(for the communication method read "ipc.text").
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Document status
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~~~~~~~~~~~~~~~
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This document is still being written, it is not finished.
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About Messages
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--------------
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Order
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~~~~~
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The client always initiates the communication.
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cinit will begin listening to messages directly after its start.
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Data
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~~~~~
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A message always conists of a predefined structure (see src/headers/comm.h).
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The byte order is host specific (may be little or big endian).
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The messages
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------------
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The client always uses the same structure (struct msg_client) to contact
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cinit. This way cinit does not need to handle dynamic data structures.
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cinit in contrast delivers different data structures to its clients,
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depending on the question.
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The questions are issued by any type of client, the internal command used is
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noted in square brackets ([]).
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The answers are given by cinit.
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Question: Start a service (and its dependencies) [CMD_START_SVC]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command is issued either by a cinit fork or by an external client.
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cinit will start a fork, which tries to start the service and its dependencies.
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The client must provide cinit with the following information:
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. Name of the service to be started
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. Reason why to start it
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. eventually additional information (see below)
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The reason
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^^^^^^^^^^
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Can be one of:
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- RS_NONE (it's a manual start request)
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- RS_WANTS (a currently starting service wants to start this service)
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- RS_NEEDS (a currently starting service needs to start this service)
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If the reason is RS_WANTS or RS_NEEDS the client must supply the name
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of the service, which wants it to be started.
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Question: Start a service (nothing else) [CMD_START_SVC_ONLY]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command may only be issued by an external client.
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cinit will start a fork, which tries to start the service and which will
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report the status back.
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Question: Stop a service (and its dependencies) [CMD_STOP_SVC]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command is issued either by a cinit fork or by an external client.
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cinit will start a fork, which tries to stop the service and each service
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that 'needs' it.
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This function works recursively, thus also killing those services, that
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need the service that need the current service.
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Question: Stop a service (nothing else) [CMD_STOP_SVC_ONLY]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command may only be issued by an external client.
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cinit will start a fork, which tries to stop this service and which will
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report the status back.
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Question: Stop a service (plus 'needs' and 'wants') [CMD_STOP_SVC_WANTS]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Same as 'Stop a service (and its dependencies)', but also stop the
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services that want to have this service.
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This function works recursively, thus also killing those services, that
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'need' or 'want' the service that 'need' or 'want' the current service.
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Question: Could you change the status? [CMD_CHG_STAT]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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A cinit fork reports the new status of a service.
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Question: Could you start the rescue mode? [CMD_RESCUE]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command may only be issued by an external client.
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cinit will not give an answer to this question.
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cinit will stop all services, kill all other processes and after that
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spawn the rescue program.
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Question: Could you halt the system? [CMD_HALT]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command may only be issued by an external client.
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cinit will not give an answer to this question.
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cinit will stop all services, kill all other processes and after that
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halt the system.
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Question: Could you reboot the system? [CMD_REBOOT]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command may only be issued by an external client.
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cinit will not give an answer to this question.
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cinit will stop all services, kill all other processes and after that
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reboot the system.
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Question: Could you poweroff the system? [CMD_POWEROFF]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command may only be issued by an external client.
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cinit will not give an answer to this question.
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cinit will stop all services, kill all other processes and after that
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poweroff the system. If poweroff is not possible, the system will
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be halted.
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Question: Could you warmboot the system? [CMD_WBOOT]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command may only be issued by an external client.
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cinit will not give an answer to this question.
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cinit will stop all services, kill all other processes and after that
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restart itself and the bootup process.
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Question: Could you send information about a service? [CMD_INFO]
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This command may only be issued by an external client.
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cinit will respond with detailled information about the service
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to the client.
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Answer: Return short status of a service
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This answer is used as a response to:
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- Question: Start a service (and its dependencies)
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- Question: Start a service (nothing else)
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- Question: Stop a service (and its dependencies)
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- Question: Stop a service (nothing else)
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- Question: Stop a service (plus 'needs' and 'wants')
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- Question: Could you change the status?
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cinit only responds the status of the asked service.
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The structure send is "asw_sstatus", which only include a status byte.
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Answer: Return long status of a service
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This answer is used as a response to:
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- Question: Could you send information about a service?
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old Messages (to be transferred into this document)
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---------------------------------------------------
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CMD_START_SVC: I want to start a service.
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CMD_CHG_STATUS: I want to change the status of a service.
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CMD_STOP_SVC: Please shutdown a service.
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CMD_RESCUE: Kill everything, and spawn a sulogin shell.
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CMD_UPDATE: Hot-reboot system and reload cinit.
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CMD_HALT: Halt the system
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CMD_REBOOT: Reboot the system
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CMD_POWEROFF: Power-off the system
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--------------------------------------------------------------------------------
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Service status:
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--------------------------------------------------------------------------------
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service status (cinit),
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Nico Schottelius 2005-09-29 (Last Modified: -)
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--------------------------------------------------------------------------------
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There are service status and service returns. Service status is a status
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a service can have. A service return is a value from a function that
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describes what happened with the service.
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Status has ST_ prefix, return has RT_ prefix.
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See cinit.h for most up to date versions.
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ST_NEED_FAIL - this service will not be started, until the needs are started
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ST_FAIL - this service failed to start
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ST_UNSPEC - some unknown error. This should never happen.
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ST_ERR - ??? /* tried earlier, service failed, won't retry */
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ST_SUCCESS - service was successfully started - senseful?
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ST_TMP - some instance is currently working on it
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ST_ONCE - executed once sucessfully
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ST_RESPAWN - service is running and respawning
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ST_TMPNOW 55 /* now you are on it - only for clients */
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#define ST_OFF 56 /* Switching service off */
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