DragonFly BSD
DragonFly users List (threaded) for 2005-12
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Re: D-BUS, anyone?

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Tue, 6 Dec 2005 10:58:35 -0800 (PST)

:Ivan Voras <ivoras@xxxxxx>
:>Something like that has been done, for example on FreeSBIE livecd of
:>FreeBSD (using devd(8) IIRC). But there's a major problem when devices
:>get disconnected (i.e.: the device gets pulled from under the mounted
:Actually it's easy to panic DragonFly (or FreeBSD, last I checked,
:which was early 5.x) by pulling out any USB device while it's in use
:-- not necessarily a storage device, it happens for me with a
:USB-to-serial convertor too, and used to happen under FreeBSD with a
:USB audio device.  Annoyingly the USB audio device was often not
:actually in use (no audio playback/recording happening, no mixer
:program running), but the kernel still believed it was in use and
:refused to "detach" it even though it was physically gone.  The panic
:happened if I plugged it in again.
:> AFAIK, this problem was considered too complex to deal at
:>this time because it involved re-architecting portions of VFS. 
:The response I got on the FreeBSD lists at that time was it would
:involve major rearchitecting of something else (not VFS) since the
:kernel assumes that a device, once detected, will always be there and
:will not be abruptly yanked out...
:I don't know if this has changed lately.

    Well, the unplug/replug->panic issue with USB on FreeBSD is simply
    due to the device being reattached but not being reinitialized properly,
    so the driver winds up getting really confused.  I fixed that in DragonFly
    but I'm sure there are a ton of other potential panic situations that
    we haven't covered.  Device Drivers just aren't written with the concept
    of the hardware getting ripped out from under them in mind.

					Matthew Dillon 

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