panic after removing usb flash disk

Kevin Oberman oberman at
Thu Aug 16 09:31:34 PDT 2007

> Date: Thu, 16 Aug 2007 22:38:23 +0800
> From: Eugene Grosbein <eugen at>
> Sender: owner-freebsd-stable at
> On Thu, Aug 16, 2007 at 04:46:11PM +0400, Roman Bogorodskiy wrote:
> > It's not a bug, it's a feature.
> Kernel panic just cannot be a feature, and other OSes do not
> panic this way. Is is design problem and it _is_ the bug
> (the hard-to-fix one).

It is NOT a bug as FreeBSD is operating as designed and documented. It
is a "mis-feature" that resulted from a change in an underlying paradigm
of the file system design. When it was developed, no one thought of
trivially removable storage like USB and Firewire drives or even
hot-pluggable (S)ATA.

Unfortunately, when something this fundamental changes, an amazing
amount of code has become intertwined in no longer valid assumptions and
a redesign based on modern, valid assumptions is a lot of work. Because
it involves some of the most complex structures in the system, it is
very unlikely that any one person can fix this. It will take a concerted
effort by a group with members reasonably expert in each of the parts to
the kernel that tie in to the old assumptions and, in a volunteer
effort like OSS, all of them need to be able to dedicate time and
resources that may conflict with day jobs. While not on the same scale,
it is not dissimilar to the SMP redesign effort that so greatly delayed
V5 and made it a rather painful version for some people to run.

To further complicate things, many of the major contributors to FreeBSD
are only interested in it for its use as a server or embedded OS. This
means that they are willing to commit resources to SMP, which they need,
but not so willing for hot-removal of storage, which is of only slight
value in the server and embedded OS world.

I am sure that a lot of people who have no professional interest in
fixing this do have a strong personal interest and I suspect that it
will happen before too long, but complaining about it is not really
going to help as almost every FreeBSD desktop and mobile user has been
bitten by this at one time or another and wants it fixed.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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