Re: panic: Negative bio_offset (-15050100712783872) on bio0xc7725d50

John-Mark Gurney wrote:
> Bernd Walter wrote this message on Wed, Sep 17, 2003 at 10:27 +0200:
> > What is wrong with returning an IO error?
> >
> > I always hated panics because of filesystem corruptions.
> > An alternative would be to just bring that filesystem down.
> > Its easy to panic a whole system with a bogus filesystem on a removeable
> > media.
> 
> If you're file system is so hosed that it does this, then panicing
> is the only safe thing to do.  You don't know what continued operation
> will do to the filesytem, and you might end up losing more data.
> 
> It is not unresonable to put parameter restrictions on function calls.
> It is not much different from enforcing that a pointer is not NULL when
> being passed as an argument.

There are several reasonable times to do parameter checking:

o	When your underlying device does not support all the
	available parameter combinations of your interface,
	but some other device does (i.e. your device is a
	subset, and you want to support it anyway, even if
	it has to offer degraded functionality).

o	When non-enforcement results in a regression for a
	third party driver or software package.

o	When the interface is intended to be a non-fragile
	one between your code and a third party's code, and
	you don't trust the third party's code not to cause
	an error in your code (you could always somewhat work
	around this one by claiming that the third party
	software caused an unrecoverable fault in passive
	voice, the way Microsoft does when VMM32.VXD gives
	out a pointer and later loses its cookies over seeing
	it given back).

That said, I think that doing parameter checking in functions for
interfaces that are non-sparsely implemented underneath is a bad
idea, and only damages performance.  I have seen this taken to
the extreme at a former employer, with disasterous results on
performance.

-- Terry