[Piglit] [PATCH v2 1/4] framework/dmesg: Adds a new module for dmesg

[Ilia Mirkin]

On Sat, Feb 1, 2014 at 3:30 AM, Dylan Baker <baker.dylan.c at gmail.com> wrote:
> This modules implements two classes and a helper function. The two
> classes are both dmesg wrapper classes, one, PosixDmesg is used on posix
> systems when requested to actually do checks on dmesg. The second class,
> DummyDmesg, is used to reduce code complexity by providing dummy
> versions of the methods in PosixDmesg. This means that we don't need
> separate code paths for Posix systems wanting to check dmesg, Posix
> systems not wanting to check dmesg, and non-posix systems which lack
> dmesg.
>
> Beyond reducing complexity this module also gives better isolation,
> dmesg is only used in Test.execute(), no where else. Additional classes
> don't need to worry about dmesg that way, it's just available.
>
> V2: - Remove unnecessary assert from PosixDmesg.update_result()
>     - simplify replace helper in PoixDmesg.update_result()
>     - replace try/except with if check
>     - Change PosixDmesg.update_dmesg() to work even if dmesg 'wraps'
>
> Signed-off-by: Dylan Baker <baker.dylan.c at gmail.com>
> ---
>  framework/dmesg.py | 147 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 147 insertions(+)
>  create mode 100644 framework/dmesg.py
>
> diff --git a/framework/dmesg.py b/framework/dmesg.py
> new file mode 100644
> index 0000000..65c3a15
> --- /dev/null
> +++ b/framework/dmesg.py
> @@ -0,0 +1,147 @@
> +# Copyright (c) 2013-2014 Intel Corporation
> +#
> +# Permission is hereby granted, free of charge, to any person obtaining a
> +# copy of this software and associated documentation files (the "Software"),
> +# to deal in the Software without restriction, including without limitation
> +# the rights to use, copy, modify, merge, publish, distribute, sublicense,
> +# and/or sell copies of the Software, and to permit persons to whom the
> +# Software is furnished to do so, subject to the following conditions:
> +#
> +# The above copyright notice and this permission notice (including the next
> +# paragraph) shall be included in all copies or substantial portions of the
> +# Software.
> +#
> +# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> +# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> +# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> +# THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> +# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> +# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
> +# IN THE SOFTWARE.
> +
> +""" Module implementing classes for reading posix dmesg """
> +
> +import os
> +import subprocess
> +
> +__all__ = ['PosixDmesg', 'DummyDmesg', 'get_dmesg']
> +
> +
> +class PosixDmesg(object):
> +    """ Read dmesg on posix systems
> +
> +    This reads the dmesg ring buffer, stores the contents of the buffer, and
> +    then compares it whenever called, returning the difference between the
> +    calls.
> +
> +    This class is not thread-safe, but with the caveat that the test reporting
> +    dmesg problems might not be the test that generated them. dmesg reporting
> +    can only be considered authoritative when running non-concurrently.
> +
> +    """
> +    DMESG_COMMAND = ['dmesg']
> +
> +    def __init__(self):
> +        """ Create a dmesg instance """
> +        self._last_message = None
> +        self._new_messages = []
> +
> +        # Populate self.dmesg initially, otherwise the first test will always
> +        # be full of dmesg crud.
> +        self.update_dmesg()
> +
> +    def update_result(self, result):
> +        """ Takes a TestResult object and updates it with dmesg statuses
> +
> +        If dmesg is enabled, and if dmesg has been updated, then replace pass
> +        with dmesg-warn and warn and fail with dmesg-fail. If dmesg has not
> +        been updated, it will return the original result passed in.
> +
> +        Arguments:
> +        result -- A TestResult instance
> +
> +        """
> +
> +        def replace(res):
> +            """ helper to replace statuses with the new dmesg status
> +
> +            Replaces pass with dmesg-warn, and warn and fail with dmesg-fail,
> +            otherwise returns the input
> +
> +            """
> +            return {"pass": "dmesg-warn",
> +                    "warn": "dmesg-fail",
> +                    "fail": "dmesg-fail"}.get(res, res)
> +
> +        # Get a new snapshot of dmesg
> +        self.update_dmesg()
> +
> +        # if update_dmesg() found new entries replace the results of the test
> +        # and subtests
> +        if self._new_messages:
> +            result['result'] = replace(result['result'])
> +
> +            # Replace any subtests
> +            if 'subtest' in result:
> +                for key, value in result['subtest'].iteritems():
> +                    result['subtest'][key] = replace(value)
> +
> +            # Add the dmesg values to the result
> +            result['dmesg'] = self._new_messages
> +
> +        return result
> +
> +    def update_dmesg(self):
> +        """ Call dmesg using subprocess.check_output
> +
> +        Get the contents of dmesg, then calculate new messages, finally set
> +        self.dmesg equal to the just read contents of dmesg.
> +
> +        """
> +        dmesg = subprocess.check_output(self.DMESG_COMMAND).strip().splitlines()
> +
> +        # Find all new entries, do this by slicing the list of dmesg to only
> +        # returns elements after the last element stored. If there are not
> +        # matches a value error is raised, that means all of dmesg is new
> +        try:
> +            self._new_messages = dmesg[dmesg.index(self._last_message) + 1:]

This will very mildly fail if you've rotated the ring buffer enough to
leave just part of the last message there, but that's unlikely enough
(and annoying enough to fix) that it's OK :)

However if you don't have timestamps enabled, then this won't quite
work either -- a lot of messages end up looking rather similar.
Especially if you're running, e.g., piglit, which triggers the same
message on 100 diff tests. I think the approach of storing the old
dmesg and then attempting to line them up would almost always produce
an accurate result... But perhaps that's too expensive and not worth
it? Dunno.

> +        except ValueError:
> +            self._new_messages = dmesg
> +
> +        # Update the last message with the last element of the dmesg snapshot
> +        self._last_message = dmesg[-1]

dmesg could also be empty (e.g. if I ran dmesg -c first)... so this
would trigger an IndexError.

> +
> +
> +class DummyDmesg(object):
> +    """ An dummy class for dmesg on non unix-like systems
> +
> +    This implements a dummy version of the PosixDmesg, and can be used anytime
> +    it is not desirable to actually read dmesg, such as non-posix systems, or
> +    when the contents of dmesg don't matter.
> +
> +    """
> +    DMESG_COMMAND = []
> +
> +    def __init__(self):
> +        pass
> +
> +    def update_dmesg(self):
> +        """ Dummy version of update_dmesg """
> +        pass
> +
> +    def update_result(self, result):
> +        """ Dummy version of update_result """
> +        return result
> +
> +
> +def get_dmesg(not_dummy=True):
> +    """ Return a Dmesg type instance
> +
> +    Normally this does a system check, and returns the type that proper for
> +    your system. However, if Dummy is True then it will always return a
> +    DummyDmesg instance.
> +
> +    """
> +    if os.name == "posix" and not_dummy:
> +        return PosixDmesg()
> +    return DummyDmesg()
> --
> 1.8.5.3
>
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