Date: Wed, 06 May 2015 23:59:00 +0200 From: "Julian H. Stacey" <jhs@berklix.com> To: NGie Cooper <yaneurabeya@gmail.com> Cc: Ryan Stone <rysto32@gmail.com>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: What's required to make removal of a mounted USB stick safe? Message-ID: <201505062159.t46Lx0iZ028607@fire.js.berklix.net> In-Reply-To: Your message "Wed, 06 May 2015 14:28:12 -0700." <CAGHfRMCRKoq7miFRrXYEmQiaHd%2BBat2t6Ab72%2BNJLW0=LQk40Q@mail.gmail.com>
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Hi, Reference:
> From: NGie Cooper <yaneurabeya@gmail.com>
> Date: Wed, 6 May 2015 14:28:12 -0700
NGie Cooper wrote:
> On Wed, May 6, 2015 at 1:49 PM, Ryan Stone <rysto32@gmail.com> wrote:
> > Currently FreeBSD stands a fair chance at panicking if a mounted USB drive
> > is removed while I/O is in flight. Does anybody know what work is involved
> > to have the kernel safely recover from this case? Losing data from the
> > drive is expected of course but there's no reason that the entire kernel
> > has to crash.
> >
> > A co-worker has been looking at this but I don't feel that we understand
> > the problem well enough to produce a real fix. All that we've been doing
> > so far is papering over the explicit panics without having a full
> > understanding of what we're doing.
>
> What version are you working on and how is the USB stick mounted (/, /mnt, etc)?
Not a new problem, it' been so over 30 years with Unix.
Remove media without umount & game over.
Some Solutions:
- Deep kernel work (dont hold your breath, see 30 above, & don't look at me :-)
- Cobble up some C to run from user space, not as root,
so that your UFS is not mounted, but accessed by user level
programs (much like mwrite & mread for accessing DOS media of old)
- man 8 amd : set a short timeout to auto unmount,
it wont total solve your problem, but should lessen the frequency of panics.
- Mount the USB media on a spare laptop running as an NFS+ AMD server,
then access the FS via NFS from your real client big PC. When
you pull the stick by accident forgetting its mounted, just the
laptop crashes afte a bit, the AMD access on the other PC just
hangs but doesnt crash.
- Encourage A SOC (google summer of code) student to look at it,
probably wont come to a solution though, see 30 above.
- Toss money at the problem :-) If your company can afford some cash, either:
- help fund FreeBSD Foundation & ask them to solve it,
- Or pay some consultant somewhere to look at it, Here's a globaly
geographicaly indexed list http://berklix.com/consultants/
maybe there's one near your company ?
Cheers,
Julian
--
Julian Stacey, BSD Linux Unix C Sys Eng Consultant Munich http://berklix.com
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