Date Wed, 6 Sep 2000 12:52:29 -0700 (PDT) From Linus Torvalds <> Subject Re: Availability of kdb



On Wed, 6 Sep 2000, Tigran Aivazian wrote:

>

> very nice monologue, thanks. It would be great to know Linus' opinion. I

> mean, I knew Linus' opinion of some years' ago but perhaps it changed? He

> is a living being and not some set of rules written in stone so perhaps

> current stability/highquality of kdb suggests to Linus that it may be

> (just maybe) acceptable into official tree?



I don't like debuggers. Never have, probably never will. I use gdb all the

time, but I tend to use it not as a debugger, but as a disassembler on

steroids that you can program.



None of the arguments for a kernel debugger has touched me in the least.

And trust me, over the years I've heard quite a lot of them. In the end,

they tend to boil down to basically:



- it would be so much easier to do development, and we'd be able to add

new things faster.



And quite frankly, I don't care. I don't think kernel development should

be "easy". I do not condone single-stepping through code to find the bug.

I do not think that extra visibility into the system is necessarily a good

thing.



Apparently, if you follow the arguments, not having a kernel debugger

leads to various maladies:

- you crash when something goes wrong, and you fsck and it takes forever

and you get frustrated.

- people have given up on Linux kernel programming because it's too hard

and too time-consuming

- it takes longer to create new features.



And nobody has explained to me why these are _bad_ things.



To me, it's not a bug, it's a feature. Not only is it documented, but it's

_good_, so it obviously cannot be a bug.



"Takes longer to create new features" - this one in particular is not a

very strong argument for having a debugger. It's not as if lack of

features or new code would be a problem for Linux, or, in fact, for the

software industry as a whole. Quite the reverse. My biggest job is to say

"no" to new features, not trying to find them.



Oh. And sure, when things crash and you fsck and you didn't even get a

clue about what went wrong, you get frustrated. Tough. There are two kinds

of reactions to that: you start being careful, or you start whining about

a kernel debugger.



Quite frankly, I'd rather weed out the people who don't start being

careful early rather than late. That sounds callous, and by God, it _is_

callous. But it's not the kind of "if you can't stand the heat, get out

the the kitchen" kind of remark that some people take it for. No, it's

something much more deeper: I'd rather not work with people who aren't

careful. It's darwinism in software development.



It's a cold, callous argument that says that there are two kinds of

people, and I'd rather not work with the second kind. Live with it.



I'm a bastard. I have absolutely no clue why people can ever think

otherwise. Yet they do. People think I'm a nice guy, and the fact is that

I'm a scheming, conniving bastard who doesn't care for any hurt feelings

or lost hours of work if it just results in what I consider to be a better

system.



And I'm not just saying that. I'm really not a very nice person. I can say

"I don't care" with a straight face, and really mean it.



I happen to believe that not having a kernel debugger forces people to

think about their problem on a different level than with a debugger. I

think that without a debugger, you don't get into that mindset where you

know how it behaves, and then you fix it from there. Without a debugger,

you tend to think about problems another way. You want to understand

things on a different _level_.



It's partly "source vs binary", but it's more than that. It's not that you

have to look at the sources (of course you have to - and any good debugger

will make that _easy_). It's that you have to look at the level _above_

sources. At the meaning of things. Without a debugger, you basically have

to go the next step: understand what the program does. Not just that

particular line.



And quite frankly, for most of the real problems (as opposed to the stupid

bugs - of which there are many, as the latest crap with "truncate()" has

shown us) a debugger doesn't much help. And the real problems are what I

worry about. The rest is just details. It will get fixed eventually.



I do realize that others disagree. And I'm not your Mom. You can use a

kernel debugger if you want to, and I won't give you the cold shoulder

because you have "sullied" yourself. But I'm not going to help you use

one, and I wuld frankly prefer people not to use kernel debuggers that

much. So I don't make it part of the standard distribution, and if the

existing debuggers aren't very well known I won't shed a tear over it.



Because I'm a bastard, and proud of it!



Linus



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