Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 1 Apr 2011 09:13:51 -0700 | Subject | Re: [PATCH 02/17] mm: mmu_gather rework |
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On Fri, Apr 1, 2011 at 5:07 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > No, although I do try to avoid it in structures because I'm ever unsure > of the storage type used. But yes, good suggestion, thanks!
I have to admit to not being a huge fan of "bool". You never know what it actually is in C, and it's a possible source of major confusion.
Some environments will make it "int", others "char", and others - like the kernel - will make it a C99/C++-like "true boolean" (C99 _Bool).
What's the difference? Integer assignment makes a hell of a difference. Do this:
long long expression = ... ... bool val = expression;
and depending on implementation it will either just truncate the value to a random number of bits, or actually do a compare with zero.
And while we use the C99 _Bool type, and thus get those true boolean semantics (ie not just be a truncated integer type), I have to say that it's still a dangerous thing to do in C because you generally cannot rely on it. There's _tons_ of software that just typedefs int or char to bool.
So even outside of structures, I'm not necessarily convinced "bool" is always such a good thing. But I'm not going to stop people from using it (inside the kernel it should be safe), I just want to raise a warning and ask people to not use it mindlessly. And avoid the casts - even if they are safe in the kernel.
Linus
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