*: Restore hook lifecycle information removed by create/start split

I expect the lifecycle information was removed accidentally in
be59415 (Split create and start, 2016-04-01, #384), because for a
time it seemed like that PR would also be removing hooks.  Putting the
lifecycle information back in, I made some tweaks to adjust to the new
environment, for example:

* Put the pre-start hooks after the 'start' call, but before the meat
  of the start call (the container-process exec trigger).  Folks who
  want a post-create hook can add one with that name.  I'd like to
  have renamed poststop to post-delete to avoid confusion like [1].
  But the motivation for keeping hooks was backwards compatibility [2]
  so I've left the name alone.

* Put each "...command is invoked..." lifecycle entry in its own list
  entry, to match the 'create' list entry.

* Move the rules about what happens on hook failure into the
  lifecycle.  This matches pre-split entries like:

    If any prestart hook fails, then the container MUST be stopped and
    the lifecycle continues at step 7.

  and avoids respecifying that information in a second location
  (config.md).

* I added the warning section to try and follow post-split's generic
  "generates an error" approach while respecting the pre-split desire
  to see what failed (we had "then an error including the exit code
  and the stderr is returned to the caller" and "then an error is
  logged").

* I left the state 'id' context out, since Michael didn't want it [3].

* Make runtime.md references to "generate an error" and "log a
  warning" links, so readers have an easier time finding more detail
  on that wording.

Where I reference a section, I'm still using the auto-generated anchor
for that header and not the anchors which were added in 41839d7 (Merge
pull request #707 from mrunalp/anchor_tags, 2017-03-03) and similar.
Mrunal suggested that the manually-added anchors were mainly intended
for the validation tooling [4].

[1]: #395
     Subject: Run post-stop hooks before the container sandbox is deleted.
[2]: #483 (comment)
     Subject: *: Remove hooks
[3]: #532 (comment)
     Subject: Restore hook language removed by create/start split
[4]: http://ircbot.wl.linuxfoundation.org/eavesdrop/%23opencontainers/%23opencontainers.2017-03-03.log.html#t2017-03-03T18:02:12

Signed-off-by: W. Trevor King <[email protected]>

config.md

@@ -368,23 +368,18 @@ The [state](runtime.md#state) of the container MUST be passed to hooks over stdi
 
 ### <a name="configHooksPrestart" />Prestart
 
-The pre-start hooks MUST be called after the container has been created, but before the user supplied command is executed.
+The pre-start hooks MUST be called after the [`start`](runtime.md#start) operation is called but [before the user-specified program command is executed](runtime.md#lifecycle).
 On Linux, for example, they are called after the container namespaces are created, so they provide an opportunity to customize the container (e.g. the network namespace could be specified in this hook).
 
-If a hook returns a non-zero exit code, an error including the exit code and the stderr MUST be returned to the caller and the container MUST be destroyed.
-
 ### <a name="configHooksPoststart" />Poststart
 
-The post-start hooks MUST be called after the user process is started.
+The post-start hooks MUST be called [after the user-specified process is executed](runtime#lifecycle) but before the [`start`](runtime.md#start) operation returns.
 For example, this hook can notify the user that the container process is spawned.
 
-If a hook returns a non-zero exit code, then an error MUST be logged and the remaining hooks are executed.
-
 ### <a name="configHooksPoststop" />Poststop
 
-The post-stop hooks MUST be called after the container process is stopped.
+The post-stop hooks MUST be called [after the container is deleted](runtime#lifecycle) but before the [`delete`](runtime.md#delete) operation returns.
 Cleanup or debugging functions are examples of such a hook.
-If a hook returns a non-zero exit code, then an error MUST be logged and the remaining hooks are executed.
 
 ### Example
 

runtime.md

@@ -52,23 +52,34 @@ The lifecycle describes the timeline of events that happen from when a container
 
 1. OCI compliant runtime's [`create`](runtime.md#create) command is invoked with a reference to the location of the bundle and a unique identifier.
 2. The container's runtime environment MUST be created according to the configuration in [`config.json`](config.md).
- If the runtime is unable to create the environment specified in the [`config.json`](config.md), it MUST generate an error.
+ If the runtime is unable to create the environment specified in the [`config.json`](config.md), it MUST [generate an error](#errors).
  While the resources requested in the [`config.json`](config.md) MUST be created, the user-specified program (from [`process`](config.md#process)) MUST NOT be run at this time.
  Any updates to [`config.json`](config.md) after this step MUST NOT affect the container.
 3. Once the container is created additional actions MAY be performed based on the features the runtime chooses to support.
  However, some actions might only be available based on the current state of the container (e.g. only available while it is started).
 4. Runtime's [`start`](runtime.md#start) command is invoked with the unique identifier of the container.
- The runtime MUST run the user-specified program, as specified by [`process`](config.md#process).
-5. The container process exits.
+5. The [prestart hooks](config.md#prestart) MUST be invoked by the runtime.
+ If any prestart hook fails, the runtime MUST [generate an error](#errors), stop the container, and continue the lifecycle at step 10.
+6. The runtime MUST run the user-specified program, as specified by [`process`](config.md#process).
+7. The [poststart hooks](config.md#poststart) MUST be invoked by the runtime.
+ If any poststart hook fails, the runtime MUST [log a warning](#warnings), but the remaining hooks and lifecycle continue as if the hook had succeeded.
+8. The container process exits.
  This MAY happen due to erroring out, exiting, crashing or the runtime's [`kill`](runtime.md#kill) operation being invoked.
-6. Runtime's [`delete`](runtime.md#delete) command is invoked with the unique identifier of the container.
- The container MUST be destroyed by undoing the steps performed during create phase (step 2).
+9. Runtime's [`delete`](runtime.md#delete) command is invoked with the unique identifier of the container.
+10. The container MUST be destroyed by undoing the steps performed during create phase (step 2).
+11. The [poststop hooks](config.md#poststop) MUST be invoked by the runtime.
+ If any poststop hook fails, the runtime MUST [log a warning](#warnings), but the remaining hooks and lifecycle continue as if the hook had succeeded.
 
 ## <a name="runtimeErrors" />Errors
 
 In cases where the specified operation generates an error, this specification does not mandate how, or even if, that error is returned or exposed to the user of an implementation.
 Unless otherwise stated, generating an error MUST leave the state of the environment as if the operation were never attempted - modulo any possible trivial ancillary changes such as logging.
 
+## <a name="runtimeWarnings" />Warnings
+
+In cases where the specified operation logs a warning, this specification does not mandate how, or even if, that warning is returned or exposed to the user of an implementation.
+Unless otherwise stated, logging a warning does not change the flow of the operation; it MUST continue as if the warning had not been logged.
+
 ## <a name="runtimeOperations" />Operations
 
 OCI compliant runtimes MUST support the following operations, unless the operation is not supported by the base operating system.
@@ -79,19 +90,19 @@ Note: these operations are not specifying any command-line APIs, and the paramet
 
 `state <container-id>`
 
-This operation MUST generate an error if it is not provided the ID of a container.
-Attempting to query a container that does not exist MUST generate an error.
+This operation MUST [generate an error](#errors) if it is not provided the ID of a container.
+Attempting to query a container that does not exist MUST [generate an error](#errors).
 This operation MUST return the state of a container as specified in the [State](#state) section.
 
 ### <a name="runtimeCreate" />Create
 
 `create <container-id> <path-to-bundle>`
 
-This operation MUST generate an error if it is not provided a path to the bundle and the container ID to associate with the container.
-If the ID provided is not unique across all containers within the scope of the runtime, or is not valid in any other way, the implementation MUST generate an error and a new container MUST NOT be created.
+This operation MUST [generate an error](#errors) if it is not provided a path to the bundle and the container ID to associate with the container.
+If the ID provided is not unique across all containers within the scope of the runtime, or is not valid in any other way, the implementation MUST [generate an error](#errors) and a new container MUST NOT be created.
 Using the data in [`config.json`](config.md), this operation MUST create a new container.
 This means that all of the resources associated with the container MUST be created, however, the user-specified program MUST NOT be run at this time.
-If the runtime cannot create the container as specified in [`config.json`](config.md), it MUST generate an error and a new container MUST NOT be created.
+If the runtime cannot create the container as specified in [`config.json`](config.md), it MUST [generate an error](#errors) and a new container MUST NOT be created.
 
 Upon successful completion of this operation the `status` property of this container MUST be `created`.
 
@@ -103,28 +114,28 @@ Any changes made to the [`config.json`](config.md) file after this operation wil
 ### <a name="runtimeStart" />Start
 `start <container-id>`
 
-This operation MUST generate an error if it is not provided the container ID.
-Attempting to start a container that does not exist MUST generate an error.
-Attempting to start an already started container MUST have no effect on the container and MUST generate an error.
+This operation MUST [generate an error](#errors) if it is not provided the container ID.
+Attempting to start a container that does not exist MUST [generate an error](#errors).
+Attempting to start an already started container MUST have no effect on the container and MUST [generate an error](#errors).
 This operation MUST run the user-specified program as specified by [`process`](config.md#process).
 
 Upon successful completion of this operation the `status` property of this container MUST be `running`.
 
 ### <a name="runtimeKill" />Kill
 `kill <container-id> <signal>`
 
-This operation MUST generate an error if it is not provided the container ID.
-Attempting to send a signal to a container that is not running MUST have no effect on the container and MUST generate an error.
+This operation MUST [generate an error](#errors) if it is not provided the container ID.
+Attempting to send a signal to a container that is not running MUST have no effect on the container and MUST [generate an error](#errors).
 This operation MUST send the specified signal to the process in the container.
 
 When the process in the container is stopped, irrespective of it being as a result of a `kill` operation or any other reason, the `status` property of this container MUST be `stopped`.
 
 ### <a name="runtimeDelete" />Delete
 `delete <container-id>`
 
-This operation MUST generate an error if it is not provided the container ID.
-Attempting to delete a container that does not exist MUST generate an error.
-Attempting to delete a container whose process is still running MUST generate an error.
+This operation MUST [generate an error](#errors) if it is not provided the container ID.
+Attempting to delete a container that does not exist MUST [generate an error](#errors).
+Attempting to delete a container whose process is still running MUST [generate an error](#errors).
 Deleting a container MUST delete the resources that were created during the `create` step.
 Note that resources associated with the container, but not created by this container, MUST NOT be deleted.
 Once a container is deleted its ID MAY be used by a subsequent container.