backend/loader/__init__.py

#! /usr/bin/python2.6
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"""
Various bootloader interfaces for pybootmgmt
"""

import sys
from bootmgmt import BootmgmtError, BootmgmtInvalidBootloaderError
from bootmgmt.bootutil import LoggerMixin
from bootmgmt.bootloader import BootLoader, ProxyBootLoader

BOOT_LOADER_BACKENDS = ['grub2', 'legacygrub', 'sbb']


class BackendBootLoaderFactory(LoggerMixin):
    """Factory that returns BootLoader instances.
    """

    @classmethod
    def get(cls, **kwargs):
        """Returns an instance of bootloader.BootLoader appropriate for the
        system identified by the keyword arguments passed in.  Invokes a
        probe function for each boot loader backend, and returns the loader
        whose probe function returned the highest rank value.  If multiple
        boot loaders' probe functions succeed, a ProxyBootLoader instance is
        returned that will manage access to both BootLoader instances.
        """
        loaderlist = []
        loader_instance = None

        for loader in BOOT_LOADER_BACKENDS:
            blmod = __name__ + '.' + loader
            __import__(blmod, level=0)
            namespc = sys.modules[blmod]
            for loaderclass in namespc.bootloader_classes():
                try:
                    loaderinst = loaderclass.probe(**kwargs)
                    if not loaderinst is None:
                        cls._debug('[PROBE SUCCEEDED] class %s',
                            loaderinst.__class__.__name__)
                        loaderlist.append(loaderinst)
                except BootmgmtError as bmerr:
                    cls._debug('Exception during probe: %s', bmerr)

        loaderclass = kwargs.get('loaderclass')
        if loaderclass:
            loaders = [x for x in loaderlist if isinstance(x, loaderclass)]
            if len(loaders) == 0:
                raise BootmgmtInvalidBootloaderError('Could not find an '
                    'instance of BootLoader class %s' % loaderclass.__name__)
            cls._debug('OVERRIDDEN [class=%s] loaderlist => %s',
                (loaderclass.__name__, loaders))
            return loaders[0]

        # Sort the loader list by decreasing rank:
        loaderlist.sort(cmp=\
            ProxyBootLoader.bootloader_cmp_by_artifacts_and_weight,
            reverse=True)

        cls._debug('loaderlist => %s', loaderlist)

        if len(loaderlist) > 1:
            bcfg = kwargs.get('bootconfig')
            if bcfg and getattr(bcfg, 'EXCLUSIVE_LOADER', False):
                cls._debug('boot config with exclusive loader requirement '
                    'detected')
                loader_instance = loaderlist[0]
            else:
                cls._debug('Creating ProxyBootLoader with primary=%s, '
                    'secondary=%s', (repr(loaderlist[0]), repr(loaderlist[1])))
                loader_instance = ProxyBootLoader(loaderlist[0], loaderlist[1])
        elif len(loaderlist) > 0:
            loader_instance = loaderlist[0]

        return loader_instance