Re: [Xen-devel] [PATCH v2 1/5] x86/hpet: Pre cleanup

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.11.13 at 17:39, Tim Deegan <tim@xxxxxxx> wrote:
> At 11:40 +0000 on 08 Nov (1383907234), Jan Beulich wrote:
>> >>> On 08.11.13 at 11:37, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>> > On 08/11/13 09:49, Jan Beulich wrote:
>> >> I very much think we should get away from the habit of prefixing
>> >> symbols with two underscores: Such names are reserved to the
>> >> compiler/platform, and the standard specifically reserves names
>> >> starting with one underscore (and not followed by an upper case
>> >> letter) for use a file scope symbols. This is what I'd like to request
>> >> be done here.
>> > 
>> > So what would you suggest?  Here, all the __$foo() are designed to end
>> > up similar to large swathes of other Xen code, implying that the
>> > appropriate spinlock should be held by the caller.
>> > 
>> > I am not too fussed which convention we use, so long as it is used
>> > consistently.
>> 
>> We obviously can't switch to the single-underscore model in one
>> go. But there are examples of this in the tree already, and I'm
>> trying to stick to this unless someone tells me not to. In the end
>> it'll really depend on others' opinions (albeit avoiding to violate the
>> standard is imo sufficiently strong an argument by itself).
> 
> IIRC the __ reservation is a posix thing, not a C one, so it doesn't
> apply to us kernel hackers. :)  But actually I would prefer to avoid
> using underscore prefixes altogether; I think they're ugly and sometimes
> slightly lazy.  (This is a relatively recent conversion -- I realise
> the shadow code is full of them!).

No, this is part of the C standard, in its description of the
requirements of a conforming library implementation:

"â All identifiers that begin with an underscore and either an
 uppercase letter or another underscore are always reserved
 for any use.
â All identifiers that begin with an underscore are always
 reserved for use as identifiers with file scope in both the
 ordinary and tag name spaces."

Irrespective of its placement in the library description, I take
this as a general rule - after all, the compiler itself also has to
have a name space it can use for itself or for communicating
with the library. And while gcc (as an example) generally
prefixes internal stuff with __builtin_, that's neither uniformly
the case there (exceptions are e.g. extended keywords), nor
a guarantee for the future, or for other compilers. Hence best
for us to stay away from using reserved names in way other
than what they're reserved for.

Jan

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