in XXX-marked comments in the recent attachment changes), this was a
long-standing bug in config.
The problem: If a device is attached to a device via an attribute exported
by that device (i.e. foo* at bar0, where 'bar' exports an attribute that
'foo' attaches to), but the device attached to is not present in the
kernel configuration file, AND another device which exports an attribute
that 'foo' attaches to _is_ present (e.g. a device baz0, if one could
specify 'foo0 at baz0'), then: the configuration file will (incorrectly)
be accepted by config, and the resulting ioconf.c will include a bogus
cfdata entry for the device (in the example, 'foo*'). This typically
causes the resulting kernel to crash during autoconfiguration.
The solution: Be much more careful about keeping track of where a device
was attached, and, in particular, if a device was attached to another device,
_always_ keep track of what device it was attached to. Then, when
cross-checking, if the attached-to device isn't present, give up and do not
check attributes. Also, document the process much more thoroughly.
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