Re: [PATCH v5 2/7] scsi: libsas: Define NCQ Priority sysfs attributes for SATA devices

[Igor Pylypiv <ipylypiv@google.com>]

On Tue, Mar 05, 2024 at 11:29:11AM +0000, John Garry wrote:
> On 05/03/2024 00:50, Igor Pylypiv wrote:
> >   static inline void sas_ata_disabled_notice(void)
> > @@ -123,6 +125,10 @@ static inline int sas_ata_add_dev(struct domain_device *parent, struct ex_phy *p
> >   	sas_ata_disabled_notice();
> >   	return -ENODEV;
> >   }
> > +
> > +static const struct attribute_group sas_ata_sdev_attr_group = {
> > +	.attrs = NULL,
> > +};
> 
> I just noticed a build issue.
> 
> With CONFIG_SCSI_SAS_ATA not set, I get this for W=1 build:
> 
> In file included from drivers/scsi/hisi_sas/hisi_sas.h:29,
>                 from drivers/scsi/hisi_sas/hisi_sas_v1_hw.c:7:
> ./include/scsi/sas_ata.h:129:37: error: ‘sas_ata_sdev_attr_group’
> defined but not used [-Werror=unused-const-variable=]
>  129 | static const struct attribute_group sas_ata_sdev_attr_group = {

Thanks for catching this, John!
For some reason I only get this warning with gcc but not with clang.

> 
> I suppose that marking sas_ata_sdev_attr_group as __maybe_unused is ok, but
> less than ideal. The linker should strip it out of files when unused.

Looks like adding the __maybe_unused attribute is a prefferred way since
it is mentioned in the Linux kernel coding style:
https://www.kernel.org/doc/html/v6.7/process/coding-style.html#conditional-compilation

Added the __maybe_unused attribute in v6. Thank you!

> 
> I think that this is also ok:
> 
> #define sas_ata_sdev_attr_group (struct attribute_group) {}
> 
> The compiler here will create a empty structure and have
> &sas_ata_sdev_attr_group point at it.
> 
> Thanks,
> John