Re: [PATCH] Use new Xen public header for product numbers and names

[Keir Fraser <keir.xen@gmail.com>]

On 01/10/2012 11:13, "Ian Jackson" <Ian.Jackson@eu.citrix.com> wrote:

> Paul Durrant writes ("RE: [Xen-devel] [PATCH] Use new Xen public header for
> product numbers and names"):
>> Ok. I'll come up with something we can use to define an array and
>> then we can iterate over that.
> 
> Great.
> 
> 
> What do people think of this preprocessor approach, which I suggested
> earlier:

My usual way to do this would be to place the list in its own header file:

pvdrivers_list.h:
EACH(WINDOWS, 0x0001, "xensource-windows")
EACH(...)
...

Then e.g.,
#define EACH(name,num,string) PVDRIVERS_ID_##name = num,
enum {
#include "pvdrivers_list.h"
}
#undef EACH

Which is a bit more abstruse on the consuming side, but does avoid the list
itself being an ugly multi-line macro monster.

I don't have a strong opinion on this by the way. :) Just saying...

 -- Keir

>   #define PVDRIVERS_LIST(EACH)                              \
>     EACH(WINDOWS, 0x0001 /* Citrix */, "xensource-windows") \
>     ...
> 
> That can be used to generate arrays, or switch statements, or
> whatever.  For example in pvdrivers.h:
> 
>   #define PVDRIVERS_EACH_ENUM(name,num,string) \
>       PVDRIVERS_ID_##name = num,
>   enum {
>       PVDRIVERS_LIST(PVDRIVERS_EACH_ENUM)
>   };
> 
> and then in qemu:
> 
>   #define PVDRIVERS_EACH_SWITCH(name,num,string) \
>      case PVDRIVERS_ID_##name:  product = string;  break;
> 
>   switch (id) {
>   PVDRIVERS_LIST(PVDRIVERS_EACH_SWITCH)
>   default:
>     sprintf blah blah
>   }
> 
> 
> If the indirect macro trick is too abstruse it's also possible to do
> this:
> 
>   #define PVDRIVERS_LIST                                              \
>     PVDRIVERS_EACH(WINDOWS, 0x0001 /* Citrix */, "xensource-windows") \
>     ...
> 
> That can be used to generate arrays, or switch statements, or
> whatever.  For example in pvdrivers.h:
> 
>   #define PVDRIVERS_EACH(name,num,string) \
>       PVDRIVERS_ID_##name = num,
>   enum {
>       PVDRIVERS_LIST
>   };
>   #undef PVDRIVERS_EACH
> 
> and then in qemu:
> 
>   #define PVDRIVERS_EACH(name,num,string) \
>      case PVDRIVERS_ID_##name:  product = string;  break;
> 
>   switch (id) {
>   PVDRIVERS_LIST
>   default:
>     sprintf blah blah
>   }
> 
>   #undef PVDRIVERS_EACH
> 
> 
> A #define containing an array initialiser is the other obvious
> alternative although of course the macro-based approaches I sketch
> above can be used to define arrays but not vice versa.
> 
> 
> Ian.
> 
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