linux-kernel - Re: [PATCH 1/2] if_enabled.h: Add IF_ENABLED_OR_ELSE() and IF

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Message-Id: <MGB1LQ.44LK9O2T0H6E1@crapouillou.net>
Date:   Tue, 08 Dec 2020 19:00:22 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...nel.org>, od@...c.me,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] if_enabled.h: Add IF_ENABLED_OR_ELSE()
 and
 IF_ENABLED() macros

Hi Randy,

Le mar. 8 déc. 2020 à 9:39, Randy Dunlap <rdunlap@...radead.org> a 
écrit :
> On 12/8/20 8:48 AM, Paul Cercueil wrote:
>> 
>>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> 
> Hi Paul,
> 
> Why not just add these 2 new macros to <linux/kconfig.h> ?
> 
> Maybe you don't want to add the other 2 headers there also?

That means including <linux/compiler.h> in <linux/kconfig.h>, which 
causes build failures:

  LD      vmlinux
  SORTTAB vmlinux
  SYSMAP  System.map
  AS      arch/mips/boot/compressed/head.o
  CC      arch/mips/boot/compressed/decompress.o
  CC      arch/mips/boot/compressed/string.o
  CC      arch/mips/boot/compressed/dummy.o
  OBJCOPY arch/mips/boot/compressed/vmlinux.bin
  HOSTCC  arch/mips/boot/compressed/calc_vmlinuz_load_addr
  GZIP    arch/mips/boot/compressed/vmlinux.bin.z
In file included from ./include/linux/kcsan-checks.h:7,
                 from ./include/asm-generic/rwonce.h:27,
                 from ./arch/mips/include/generated/asm/rwonce.h:1,
                 from ./include/linux/compiler.h:246,
                 from ././include/linux/kconfig.h:8,
                 from <command-line>:32:
/include/linux/compiler_attributes.h:64: warning: "__always_inline" 
redefined
   64 | #define __always_inline                 inline 
__attribute__((__always_inline__))
      |
In file included from ./include/linux/stddef.h:5,
                 from ./include/uapi/linux/posix_types.h:5,
                 from ./include/uapi/linux/types.h:14,
                 from ./include/linux/types.h:6,
                 from ./include/linux/kasan-checks.h:5,
                 from ./include/asm-generic/rwonce.h:26,
                 from ./arch/mips/include/generated/asm/rwonce.h:1,
                 from ./include/linux/compiler.h:246,
                 from ././include/linux/kconfig.h:8,
                 from <command-line>:32:
/include/uapi/linux/stddef.h:5: note: this is the location of the 
previous definition
    5 | #define __always_inline inline
      |
In file included from ./arch/mips/include/generated/asm/rwonce.h:1,
                 from ./include/linux/compiler.h:246,
                 from ././include/linux/kconfig.h:8,
                 from <command-line>:32:
/include/asm-generic/rwonce.h:64:31: error: expected ‘;’ before 
‘unsigned’
   64 | static __no_sanitize_or_inline
      |                               ^
      |                               ;
   65 | unsigned long __read_once_word_nocheck(const void *addr)
      | ~~~~~~~~
/include/asm-generic/rwonce.h:65:15: warning: no previous prototype 
for ‘__read_once_word_nocheck’ [-Wmissing-prototypes]
   65 | unsigned long __read_once_word_nocheck(const void *addr)
      |               ^~~~~~~~~~~~~~~~~~~~~~~~
/include/asm-generic/rwonce.h:82:28: error: expected ‘;’ before 
‘unsigned’
   82 | static __no_kasan_or_inline
      |                            ^
      |                            ;
   83 | unsigned long read_word_at_a_time(const void *addr)
      | ~~~~~~~~
/include/asm-generic/rwonce.h:83:15: warning: no previous prototype 
for ‘read_word_at_a_time’ [-Wmissing-prototypes]
   83 | unsigned long read_word_at_a_time(const void *addr)
      |               ^~~~~~~~~~~~~~~~~~~


That's why I opted for a new header.

Cheers,
-Paul

>>  ---
>>   include/linux/if_enabled.h | 22 ++++++++++++++++++++++
>>   1 file changed, 22 insertions(+)
>>   create mode 100644 include/linux/if_enabled.h
>> 
>>  diff --git a/include/linux/if_enabled.h b/include/linux/if_enabled.h
>>  new file mode 100644
>>  index 000000000000..8189d1402340
>>  --- /dev/null
>>  +++ b/include/linux/if_enabled.h
>>  @@ -0,0 +1,22 @@
>>  +/* SPDX-License-Identifier: GPL-2.0 */
>>  +#ifndef __LINUX_IF_ENABLED_H
>>  +#define __LINUX_IF_ENABLED_H
>>  +
>>  +#include <linux/build_bug.h>
>>  +#include <linux/compiler_types.h>
>>  +#include <linux/kconfig.h>
>>  +
>>  +/*
>>  + * IF_ENABLED_OR_ELSE(CONFIG_FOO, a, b) evaluates to (a) if 
>> CONFIG_FOO is set
>>  + * to 'y' or 'm', (b) otherwise.
>>  + */
>>  +#define IF_ENABLED_OR_ELSE(option, a, b) \
>>  +	(BUILD_BUG_ON_ZERO(__same_type((a), (b))) || IS_ENABLED(option) ? 
>> (a) : (b))
>>  +
>>  +/*
>>  + * IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is 
>> set to 'y'
>>  + * or 'm', NULL otherwise.
>>  + */
>>  +#define IF_ENABLED(option, ptr) IF_ENABLED_OR_ELSE(option, ptr, 
>> NULL)
>>  +
>>  +#endif /* __LINUX_IF_ENABLED_H */
>> 
> 
> 
> thanks.
> --
> ~Randy
>