On Mon, 5 Feb 2007, Alan wrote:
>
> It works both ways. If I don't need to know that I must select SCSI then
> it turns on easily. If I want to turn SCSI off then it causes mayhem. Two
> sides of the same coin.
They are not really symmetric, though.
There's two big issues:
- tuning things "on" is more likely to cause a working kernel.
This is pretty fundamental. It's almost always simply more correct to
add features than remove them. At worst, it won't be used.
This argues that you should have to "work less" to turn something on,
and in particular, you should need to _know_ less. To turn something
off, you not only need to know how to turn it off, you fundamentally
need to know something much bigger: you need to know that you
really don't need it in the first place.
The interaction of CONFIG_ATA/CONFIG_SCSI is an example of the latter.
You really *do* need to know more to turn off SCSI - because you need
to know that the ATA layer depends on it.
So in the absense of knowledge, turning things on is better.
- A developer who really wants to turn things off, and knows enough that
that is actually safe, can really just do a "grep" for it. If you're
_extremely_ knowledgeable, you can do something like
git grep 'select.*\<SCSI\>' -- '*onfig*'
and that easily finds you the (currently single) place that turns on
SCSI (and yes, you can try it with I2C too, and try to recursively
figure out what it is that turns on I2C even though you *tried* to turn
it off. I2C - the option that just wouldn't die! ;)
So I agree that they are two facets of the same coin, but I claim that
there's a huge reason why they are not mirror-images - there are often
reasons to prefer one over the other.
That said: I really don't think "depends on" should just always be
"select" either. There's a balance:
- you use "depends on" when you can ask a simple question like "what kind
of machine do you have" or "do you want to support USB" or "do you have
SCSI devices".
But even then, you might end up having some devices that are
*technically* USB, but people don't think of them that way (for
example, some laptop add-ons are literally USB devices that are "built
into" the laptop - you might well decide to show those choices even if
somebody said "no USB", and if he then says "yeah, I have one of those
things", you just know he wasn't clueful enough, and you enable USB
behind his back _anyway_. Exact same thing as with SATA support)
- you use "select" when the question more naturally went the other way
(because the infrastructure isn't obvious)
So they are two similar things, and which one to choose mainly depends on
how you want to phrase the question - not on technical issues per se.
So neither is "wrong". They both have their downsides.
Linus
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