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From: Linus Torvalds <torvalds@linux-foundation.org>
To: George Spelvin <linux@horizon.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Waiman Long <waiman.long@hp.com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount
Date: Sat, 31 Aug 2013 10:16:52 -0700	[thread overview]
Message-ID: <CA+55aFz7k5zUvJdZxpZgCgfx_-PT+f-9J50hnC1i3x=8_dXkBw@mail.gmail.com> (raw)
In-Reply-To: <20130831030633.28455.qmail@science.horizon.com>

On Fri, Aug 30, 2013 at 8:06 PM, George Spelvin <linux@horizon.com> wrote:
> Just noticing that you are adding several functions that return a boolean
> value as an int.  And a "gotref" local variable.
>
> Is that just not wanting to bother with thse newfangled C99 innovations,
> or do you dislike the "bool" type for some reason?

I don't use "bool" in code I write. I don't think it adds any actual
value, and I think the data type is badly designed and of dubious
value in C. It has very few actual advantages.

That said, it's not like I *hate* the type, and I won't remove bool
from code other people write. I just think it's superfluous and
stupid, and another case of C++ people thinking too much "this is a
cool feature" without then actually doing it well. The C people then
picked it up because it was less onerous than some other C++ features,
and all the compilers had the logic anyway.

If "bool" had real advantages (like having a dense array
representation, for example), that would be one thing. It doesn't.
Sure, now you can take an address of a bool (which you couldn't
generally do efficiently if it really was a bit array), but it also
means that in practice, "bool" is normally nothing but "char" with
some really odd and special implicit type casting rules.

I doubt most people really even understand how "bool" casting works.

And bool is actually really *dangerous* to use if you don't understand
it. There are people who use "bool", but then because they want to be
portable, they have a compatibility #ifdef or other configuration
thing that does something like

   typedef int bool;
   #define true 1
   #define false 0

and it will actually work. Most of the time. And then the semantic
differences from a _real_ C compiler that supports the C99 _Bool/bool
type are really really subtle.

IOW, bool has very few real upsides, and it has a real downside: it's
subtle, and people really never even seem to _realize_ just how subtle
it is.  I suspect that if you ask ten random average C programmers if
the above is equivalent to stdbool.h, nine of them will say "sure".

And they'd be *COMPLETELY* wrong.

So no. I'm definitely not a fan of bool. I think there are better
types, and I think there are better ways to document things.

                     Linus

  reply	other threads:[~2013-08-31 17:16 UTC|newest]

Thread overview: 146+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-08-31  3:06 [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount George Spelvin
2013-08-31 17:16 ` Linus Torvalds [this message]
2013-09-01  8:50   ` George Spelvin
2013-09-01 11:10     ` Theodore Ts'o
2013-09-01 15:49       ` Linus Torvalds
2013-09-01 18:11         ` Steven Rostedt
2013-09-01 20:03           ` Linus Torvalds
  -- strict thread matches above, loose matches on Subject: below --
2013-08-06  3:12 [PATCH v7 0/4] Lockless update of reference count protected by spinlock Waiman Long
2013-08-06  3:12 ` [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount Waiman Long
2013-08-29  1:40   ` Linus Torvalds
2013-08-29  4:44     ` Benjamin Herrenschmidt
2013-08-29  7:00       ` Ingo Molnar
2013-08-29 16:43         ` Linus Torvalds
2013-08-29 19:25           ` Linus Torvalds
2013-08-29 23:42             ` Linus Torvalds
2013-08-30  0:26               ` Benjamin Herrenschmidt
2013-08-30  0:49                 ` Linus Torvalds
2013-08-30  2:06                   ` Michael Neuling
2013-08-30  2:30                     ` Benjamin Herrenschmidt
2013-08-30  2:35                       ` Linus Torvalds
2013-08-30  2:45                         ` Benjamin Herrenschmidt
2013-08-30  2:31                     ` Linus Torvalds
2013-08-30  2:43                       ` Benjamin Herrenschmidt
2013-08-30  7:16                   ` Ingo Molnar
2013-08-30 15:28                     ` Linus Torvalds
2013-08-30  3:12               ` Waiman Long
2013-08-30  3:54                 ` Linus Torvalds
2013-08-30  7:55                   ` Sedat Dilek
2013-08-30  8:10                     ` Sedat Dilek
2013-08-30  9:27                     ` Sedat Dilek
2013-08-30  9:48                       ` Ingo Molnar
2013-08-30  9:56                         ` Sedat Dilek
2013-08-30  9:58                           ` Sedat Dilek
2013-08-30 10:29                             ` Sedat Dilek
2013-08-30 10:36                               ` Peter Zijlstra
2013-08-30 10:44                                 ` Sedat Dilek
2013-08-30 10:46                                   ` Sedat Dilek
2013-08-30 10:52                                   ` Peter Zijlstra
2013-08-30 10:57                                     ` Sedat Dilek
2013-08-30 14:05                                       ` Sedat Dilek
2013-08-30 11:19                                 ` Sedat Dilek
2013-08-30 10:38                               ` Sedat Dilek
2013-08-30 15:34                       ` Linus Torvalds
2013-08-30 15:38                         ` Sedat Dilek
2013-08-30 16:12                           ` Steven Rostedt
2013-08-30 16:16                             ` Sedat Dilek
2013-08-30 18:42                             ` Linus Torvalds
2013-08-30 16:32                           ` Linus Torvalds
2013-08-30 16:37                             ` Sedat Dilek
2013-08-30 16:52                               ` Linus Torvalds
2013-08-30 17:11                                 ` Sedat Dilek
2013-08-30 17:26                                   ` Linus Torvalds
2013-09-01 10:01                                 ` Sedat Dilek
2013-09-01 10:33                                   ` Sedat Dilek
2013-09-01 15:32                                   ` Linus Torvalds
2013-09-01 15:45                                     ` Sedat Dilek
2013-09-01 15:55                                       ` Linus Torvalds
2013-09-02 10:30                                         ` Sedat Dilek
2013-09-02 16:09                                           ` David Ahern
2013-09-01 20:59                                     ` Linus Torvalds
2013-09-01 21:23                                       ` Al Viro
2013-09-01 22:16                                         ` Linus Torvalds
2013-09-01 22:35                                           ` Al Viro
2013-09-01 22:44                                             ` Al Viro
2013-09-01 22:58                                               ` Linus Torvalds
2013-09-01 22:48                                           ` Linus Torvalds
2013-09-01 23:30                                             ` Al Viro
2013-09-02  0:12                                               ` Linus Torvalds
2013-09-02  0:50                                                 ` Linus Torvalds
2013-09-02  7:05                                                   ` Ingo Molnar
2013-09-02 16:44                                                     ` Linus Torvalds
2013-09-03 10:15                                                       ` Ingo Molnar
2013-09-03 15:41                                                         ` Linus Torvalds
2013-09-03 18:34                                                           ` Linus Torvalds
2013-09-03 19:19                                                             ` Ingo Molnar
2013-09-03 21:05                                                               ` Linus Torvalds
2013-09-03 21:13                                                                 ` Linus Torvalds
2013-09-03 21:34                                                                   ` Linus Torvalds
2013-09-03 21:39                                                                     ` Linus Torvalds
2013-09-03 14:08                                                       ` Pavel Machek
2013-09-03 22:37                                     ` Sedat Dilek
2013-09-03 22:55                                       ` Dave Jones
2013-09-03 23:05                                         ` Sedat Dilek
2013-09-03 23:15                                           ` Dave Jones
2013-09-03 23:20                                             ` Sedat Dilek
2013-09-03 23:45                                       ` Sedat Dilek
2013-08-30 18:33                   ` Waiman Long
2013-08-30 18:53                     ` Linus Torvalds
2013-08-30 19:20                       ` Waiman Long
2013-08-30 19:33                         ` Linus Torvalds
2013-08-30 20:15                           ` Waiman Long
2013-08-30 20:43                             ` Linus Torvalds
2013-08-30 20:54                               ` Al Viro
2013-08-30 21:03                                 ` Linus Torvalds
2013-08-30 21:44                                   ` Al Viro
2013-08-30 22:30                                     ` Linus Torvalds
2013-08-31 21:23                                       ` Al Viro
2013-08-31 22:49                                         ` Linus Torvalds
2013-08-31 23:27                                           ` Al Viro
2013-09-01  0:13                                             ` Al Viro
2013-09-01 17:48                                               ` Al Viro
2013-09-09  8:30                                               ` Peter Zijlstra
2013-08-30 21:10                                 ` Waiman Long
2013-08-30 21:22                                   ` Linus Torvalds
2013-08-30 21:30                                   ` Al Viro
2013-08-30 21:42                                     ` Waiman Long
2013-08-30 19:40                         ` Al Viro
2013-08-30 19:52                           ` Waiman Long
2013-08-30 20:26                             ` Al Viro
2013-08-30 20:35                               ` Waiman Long
2013-08-30 20:48                                 ` Al Viro
2013-08-31  2:02                                   ` Waiman Long
2013-08-31  2:35                                     ` Al Viro
2013-08-31  2:42                                       ` Al Viro
2013-09-02 19:25                                         ` Waiman Long
2013-09-03  6:01                                           ` Ingo Molnar
2013-09-03  7:24                                             ` Sedat Dilek
2013-09-03 15:38                                               ` Linus Torvalds
2013-09-03 15:14                                             ` Waiman Long
2013-09-03 15:34                                               ` Linus Torvalds
2013-09-03 19:09                                                 ` Linus Torvalds
2013-09-03 21:01                                                   ` Waiman Long
2013-09-04 14:52                                                   ` Waiman Long
2013-09-04 15:14                                                     ` Linus Torvalds
2013-09-04 19:25                                                       ` Waiman Long
2013-09-04 21:34                                                         ` Linus Torvalds
2013-09-05  2:35                                                           ` Waiman Long
2013-09-05 13:31                                                     ` Ingo Molnar
2013-09-05 17:33                                                       ` Waiman Long
2013-09-05 17:40                                                         ` Ingo Molnar
2013-09-03 22:41                                               ` Sedat Dilek
2013-09-03 23:11                                                 ` Sedat Dilek
2013-09-08 21:45               ` Linus Torvalds
2013-09-09  0:03                 ` Al Viro
2013-09-09  0:25                   ` Linus Torvalds
2013-09-09  0:35                     ` Al Viro
2013-09-09  0:38                       ` Linus Torvalds
2013-09-09  0:57                         ` Al Viro
2013-09-09  2:09                     ` Ramkumar Ramachandra
2013-09-09  0:30                   ` Al Viro
2013-09-09  3:32                   ` Linus Torvalds
2013-09-09  4:06                     ` Ramkumar Ramachandra
2013-09-09  5:44                     ` Al Viro
2013-08-30 17:17           ` Peter Zijlstra
2013-08-30 17:28             ` Linus Torvalds
2013-08-30 17:33               ` Linus Torvalds
2013-08-29 15:20     ` Waiman Long

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