Re: [Xen-devel] [PATCH 5/7] public / x86: introduce __HYPERCALL_iommu_op

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.06.18 at 13:42, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 16 March 2018 12:25
>> >>> On 12.02.18 at 11:47, <paul.durrant@xxxxxxxxxx> wrote:
>> > --- a/xen/arch/x86/Makefile
>> > +++ b/xen/arch/x86/Makefile
>> > @@ -33,6 +33,7 @@ obj-$(CONFIG_CRASH_DEBUG) += gdbstub.o
>> >  obj-y += hypercall.o
>> >  obj-y += i387.o
>> >  obj-y += i8259.o
>> > +obj-y += iommu_op.o
>> 
>> As mentioned in other contexts, I'd prefer if we stopped using
>> underscores in places where dashes (or other separators not
>> usable in C identifiers) are fine.
> 
> I don't see any guidance in CODING_STYLE or elsewhere, and also the majority 
> of the codebase seems to prefer using underscores in module names. Personally 
> I'd prefer new code remain consistent.

The lack of statement to this effect is why I've said "I'd prefer". See
alternative-asm.h, x86-defns.h, or x86-vendors.h for _recent_
examples of moving into the other direction. On all keyboards I've
seen or used, an underscore requires two keys to be pressed, while
a dash takes only one. This isn't much for an individual instance, but
it sums up. It's the same reason why I'm advocating against the use
of underscores in new command line option names.

In the end, looking at the history of typography, I think underscore
is a relatively late (and presumably artificial) addition; in particular I
don't recall mechanical type writers to even have a key for it. It's
use as a visual separator is necessary in e.g. programming
languages, as commonly dash designated the operator for "minus"
there. Extending such naming to non-identifiers (file system names
and command line options are just prominent examples) is simply
misguided imo.

>> > --- /dev/null
>> > +++ b/xen/include/public/iommu_op.h
>> > @@ -0,0 +1,55 @@
>> > +/*
>> > + * Permission is hereby granted, free of charge, to any person obtaining a
>> copy
>> > + * of this software and associated documentation files (the "Software"),
>> to
>> > + * deal in the Software without restriction, including without limitation 
>> > the
>> > + * rights to use, copy, modify, merge, publish, distribute, sublicense,
>> and/or
>> > + * sell copies of the Software, and to permit persons to whom the
>> Software is
>> > + * furnished to do so, subject to the following conditions:
>> > + *
>> > + * The above copyright notice and this permission notice shall be included
>> in
>> > + * all copies or substantial portions of the Software.
>> > + *
>> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
>> KIND, EXPRESS OR
>> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
>> MERCHANTABILITY,
>> > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO
>> EVENT SHALL THE
>> > + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
>> DAMAGES OR OTHER
>> > + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
>> OTHERWISE, ARISING
>> > + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
>> OR OTHER
>> > + * DEALINGS IN THE SOFTWARE.
>> > + *
>> > + * Copyright (C) 2018 Citrix Systems Inc
>> > + */
>> > +
>> > +#ifndef __XEN_PUBLIC_IOMMU_OP_H__
>> > +#define __XEN_PUBLIC_IOMMU_OP_H__
>> 
>> Please can you avoid introducing further name space violations
>> into the public headers?
> 
> I assume you mean the leading '__'? Again, I chose the name based on 
> consistency with other code and I'd prefer to remain consistent. Could you 
> explain why having a leading '__' is problematic?

Names starting with double underscores are reserved (as are, btw,
names starting with a single underscore and an upper case letter).
While it's unlikely for a compiler to ever want to use
__XEN_PUBLIC_IOMMU_OP_H__ for its internal purposes, we couldn't
validly complain if one did.

Jan



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel