Re: [PATCH] debugfs: fix debugfs_real_fops() build error

[Greg Kroah-Hartman]

On Tue, Nov 14, 2017 at 12:40:31PM +0100, Arnd Bergmann wrote:
> Some drivers use debugfs_real_fops() even when CONFIG_DEBUG_FS is disabled,
> which now leads to a build error:
> 
> In file included from include/linux/list.h:9:0,
>                  from include/linux/wait.h:7,
>                  from include/linux/wait_bit.h:8,
>                  from include/linux/fs.h:6,
>                  from drivers/net/wireless/broadcom/b43legacy/debugfs.c:26:
> drivers/net/wireless/broadcom/b43legacy/debugfs.c: In function 'b43legacy_debugfs_read':
> drivers/net/wireless/broadcom/b43legacy/debugfs.c:224:23: error: implicit declaration of function 'debugfs_real_fops'; did you mean 'debugfs_create_bool'? [-Werror=implicit-function-declaration]
> 
> My first impulse was to add another 'static inline' dummy function
> returning NULL for it, which would work fine. However, most callers
> feed the pointer into container_of(), so it seems a little dangerous
> here. Since all the callers are inside of a read/write file operation
> that gets eliminated in this configuration, so having an 'extern'
> declaration seems better here. If it ever gets used in a dangerous
> way, that will now result in a link error.

Ok, but does your patch really "fix" anything?  The linker should now
complain, not the compiler, for these types of configurations?

thanks,

greg k-h