Abstract getting unique status result into a single method

[mulkieran]

Related: https://github.com/stratis-storage/stratisd/issues/794.
Related: #221.

The goals of this PR are:

• Remove some assertions, and replace them with errors, since the assertions are not logically necessary.
• Make reading the target type when parsing the ioctl a bit safer in order to
• Extend the implementation of FromStr for the various status types by having it parse the target type. This bring FromStr for status types in line with FromStr for param types.
• Get rid of some unnecessary code duplication.

The changes in behavior are:

• Where previously an error in parsing might result in an assertion failure, now the error would result in an error return with a more helpful message.
• If it was ever possible for a target type to have a trailing space at the end, now it is not. This makes checking equality of target types a less chancy proposition.
• If a status line for an unexpected target type is parsed, a failure will occur when the target type is compared with the expected one, rather than later, when the actual fields of the status are parsed with incorrect expectations.

EDIT: Comments:

• Abstract getting unique status result into a single method #430 (comment)
• Abstract getting unique status result into a single method #430 (comment)
• Abstract getting unique status result into a single method #430 (comment)
• Abstract getting unique status result into a single method #430 (comment)
  properly belong to issue Devicemapper status ioctl sometimes returns a single word status "Error" #431, rather than to this PR.

[tasleson]

I just built a local copy of stratisd using this branch. I created a pool with 3 devices, started IO on the FS created from it and then took the block devices offline. The stratsd process printed:

ERROR libstratis::engine::strat_engine::thinpool::thinpool: Thinpool status is fail -> Failed

Running the command line results in exception:

# stratis pool
Traceback (most recent call last):
  File "/home/tasleson/projects/stratis/dbus-python-client-gen/src/dbus_python_client_gen/_invokers.py", line 319, in dbus_func
    return dbus_method(*xformed_args, timeout=timeout)
  File "/usr/lib64/python3.6/site-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib64/python3.6/site-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
dbus.exceptions.DBusException: org.freedesktop.DBus.Error.Failed: no total physical size computed for pool with uuid 3b8e5c85-a0d8-4b04-ab5e-826689e7d020

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/tasleson/projects/stratis/stratis-cli/src/stratis_cli/_main.py", line 48, in the_func
    result.func(result)
  File "/home/tasleson/projects/stratis/stratis-cli/src/stratis_cli/_actions/_top.py", line 68, in list_pools
    managed_objects = ObjectManager.Methods.GetManagedObjects(proxy, {})
  File "/home/tasleson/projects/stratis/dbus-python-client-gen/src/dbus_python_client_gen/_invokers.py", line 327, in dbus_func
    name, xformed_args)) from err
dbus_python_client_gen._errors.DPClientInvocationError: Error while invoking method "GetManagedObjects" belonging to interface "org.freedesktop.DBus.ObjectManager" with arguments ()

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/tasleson/projects/stratis/stratis-cli/bin/stratis", line 33, in <module>
    main()
  File "/home/tasleson/projects/stratis/stratis-cli/bin/stratis", line 29, in main
    return run()(sys.argv[1:])
  File "/home/tasleson/projects/stratis/stratis-cli/src/stratis_cli/_main.py", line 52, in the_func
    raise StratisCliActionError(command_line_args, result) from err
stratis_cli._errors.StratisCliActionError: Action selected by command-line arguments ['--propagate', 'pool'] which were parsed to Namespace(func=<function TopActions.list_pools at 0x7fb4e364e6a8>, propagate=True) failed

So we aren't panicing the stratisd process, but the CLI is not usable.

[mulkieran]

I think the problem is flaky; hopefully it will recur. Maybe it depends on calling the command line at just the correct time. Whoops. Look at the error for the first exception. dbus.exceptions.DBusException: org.freedesktop.DBus.Error.Failed: no total physical size computed for pool with uuid 3b8e5c85-a0d8-4b04-ab5e-826689e7d020. stratisd is now taking the error from devicemapper, throwing it away, and stuffing in a generic error. We need to edit stratisd to send back the real info, somehow.

[mulkieran]

@tasleson: Please add stratis-storage/stratisd#1449 to your stratisd install and see what the D-Bus tells us then.

[tasleson]

@mulkieran As requested

# stratis pool list
Traceback (most recent call last):
  File "/home/tasleson/projects/stratis/dbus-python-client-gen/src/dbus_python_client_gen/_invokers.py", line 319, in dbus_func
    return dbus_method(*xformed_args, timeout=timeout)
  File "/usr/lib64/python3.6/site-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib64/python3.6/site-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
dbus.exceptions.DBusException: org.freedesktop.DBus.Error.Failed: no total physical size computed for pool with uuid b9e2b3f8-c085-44d4-9493-8636c2801947, cause: DM error: DM error: Invalid: Insufficient number of fields for status; requires at least 8, found only 1 in status line "Error"

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/tasleson/projects/stratis/stratis-cli/src/stratis_cli/_main.py", line 48, in the_func
    result.func(result)
  File "/home/tasleson/projects/stratis/stratis-cli/src/stratis_cli/_actions/_top.py", line 68, in list_pools
    managed_objects = ObjectManager.Methods.GetManagedObjects(proxy, {})
  File "/home/tasleson/projects/stratis/dbus-python-client-gen/src/dbus_python_client_gen/_invokers.py", line 327, in dbus_func
    name, xformed_args)) from err
dbus_python_client_gen._errors.DPClientInvocationError: Error while invoking method "GetManagedObjects" belonging to interface "org.freedesktop.DBus.ObjectManager" with arguments ()

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/tasleson/projects/stratis/stratis-cli/bin/stratis", line 33, in <module>
    main()
  File "/home/tasleson/projects/stratis/stratis-cli/bin/stratis", line 29, in main
    return run()(sys.argv[1:])
  File "/home/tasleson/projects/stratis/stratis-cli/src/stratis_cli/_main.py", line 52, in the_func
    raise StratisCliActionError(command_line_args, result) from err
stratis_cli._errors.StratisCliActionError: Action selected by command-line arguments ['--propagate', 'pool', 'list'] which were parsed to Namespace(func=<function TopActions.list_pools at 0x7f2c82f7b6a8>, propagate=True) failed

[mulkieran]

Bingo! I think this needs a separate issue since the problem that has been located has nothing to do with this PR. See #431.

[mulkieran]

rebased.

[mulkieran]

rebased.

[mulkieran]

I think there's potential for a test, so pulling out of review...

[mulkieran]

rebased.