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CVS commit: src/sys

Module Name:    src
Committed By:   dyoung
Date:           Thu Nov 12 19:10:31 UTC 2009

Modified Files:
        src/sys/kern: subr_autoconf.c
        src/sys/sys: device.h

Log Message:
Move a device-deactivation pattern that is replicated throughout
the system into config_deactivate(dev): deactivate dev and all of
its descendants.  Block all interrupts while calling each device's
activation hook, ca_activate.  Now it is possible to simplify or
to delete several device-activation hooks throughout the system.

Do not deactivate a driver while detaching it!  If the driver was
already deactivated (because of accidental/emergency removal), let
the driver cope with the knowledge that DVF_ACTIVE has been cleared.
Otherwise, let the driver access the underlying hardware (so that
it can flush caches, restore original register settings, et cetera)
until it exits its device-detachment hook.

Let multiple readers and writers simultaneously access the system's
device_t list, alldevs, from either interrupt or thread context:
postpone changing alldevs linkages and freeing autoconf device
structures until a garbage-collection phase that runs after all
readers & writers have left the list.

Give device iterators (deviter(9)) a consistent view of alldevs no
matter whether device_t's are added and deleted during iteration:
keep a global alldevs generation number.  When an iterator enters
alldevs, record the current generation number in the iterator and
increase the global number.  When a device_t is created, label it
with the current global generation number.  When a device_t is
deleted, add a second label, the current global generation number.
During iteration, compare a device_t's added- and deleted-generation
with the iterator's generation and skip a device_t that was deleted
before the iterator entered the list or added after the iterator
entered the list.

The alldevs generation number is never 0.  The garbage collector
reaps device_t's whose delete-generation number is non-zero.

Make alldevs private to sys/kern/subr_autoconf.c.  Use deviter(9)
to access it.

To generate a diff of this commit:
cvs rdiff -u -r1.186 -r1.187 src/sys/kern/subr_autoconf.c
cvs rdiff -u -r1.124 -r1.125 src/sys/sys/device.h

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.

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