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SubjectRe: [2.6 patch] let broken drivers depend on BROKEN{,ON_SMP}
On Wed, Jul 30, 2003 at 12:29:55PM +0100, John Bradford wrote:
> > > > * Driver does not work, and is thus disabled. If it is not
> > > > fixed in the near future, it will be considered to be
> > > > OBSOLETE as well.
> > > >
> > >
> > > Please do _NOT_ do this - there is a far more important and worthwhile
> > > reason to have a CONFIG_BROKEN than to simply save the few minutes of
> > > inconvenience that including a non-compiling option in a kernel build
> > > causes.
> > >
> > > Imagine the situation where a driver such as a SCSI driver builds
> > > successfully, but it silently corrupts data under certain, (possibly
> > > rare), circumstances.
> > >
> > > In that case, it's important to warn people that it's broken, because
> > > it's not necessarily obvious, and could case significant data loss.
> > > If something doesn't compile, it already gives you an error message.
> > > The only problem is a few minutes of wasted time.
> >
> > You forget one important thing:
> > If a _user_ of a stable kernel notices "it doesn't even compile" this
> > gives a very bad impression of the quality of the Linux kernel.
> I don't agree. The stock kernel is a work in progress, and things get
> broken from time to time as a normal part of development. Experienced
> users will realise that, and I wouldn't encourage inexperienced users
> to compile their own kernel from the stock trees anyway, because they
> could easily miss bugfixes, including data corruption and security
> ones, simply because they assume that they are in the mainline
> kernel.

Whether you like it or not:

Many non-kernel-hackers compile their own kernels.

Even if you wouldn't encourage them, there are enough situations where
they can't choose:

It occurs often that a fix or support for some hardware is only in the
latest -pre or in the -ac tree.

You say "things get broken from time to time as a normal part of
development". Ideally this should never happen in a stable series. We
don't live in an ideal world, but we should try to be as close as
possible to this goal.

> Compiling your own kernel from the stock kernel trees is still
> something that should be considered for experienced users only.
> Besides, what's worse? Possible data corruption or a bad impression?

Possible data corruption is worse, but completely disabling this driver
is even better.

> > > > * Driver works on uniprocessor but not on SMP and is thus
> > > > disabled when compiling for SMP. It is assumed that the
> > > > driver will be fixed for SMP if relevant.
> > > >
> > >
> > > Please _don't_ do this either. It implies that if
> > > CONFIG_BROKEN_ON_SMP isn't set, then it's SMP safe - a lot of drivers
> > > will NOT have been tested on SMP, so it's a bad thing to assume that
> > > is the case.
> > >...
> >
> > My patch adds BROKEN_ON_SMP only to drivers that don't compile, but if a
> > driver causes e.g. data corruption on SMP I don't see a reason against
> > letting it depend on BROKEN_ON_SMP.
> The name BROKEN_ON_SMP implies that if you don't set it, what's left
> is known to work on SMP. In a lot of cases, it'll actually be
> untested on SMP.

Say which other drivers are completely broken on SMP without a fix
available or in the near future and it's easy to add a BROKEN_ON_SMP.

As long as noone reports such a bug I assume a driver works.

> John.



"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed

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