Re: [PATCH v4 10/14] gunyah: sysfs: Add node to describe supported features

[Jeff Johnson]

On 9/29/2022 12:36 AM, Joe Perches wrote:
> On Wed, 2022-09-28 at 12:56 -0700, Elliot Berman wrote:
> > Add a sysfs node to list the features that the Gunyah hypervisor and
> > Linux supports. For now, Linux support cspace (capability IDs) and
> > message queues, so only report those..
> []
> > diff --git a/drivers/virt/gunyah/sysfs.c b/drivers/virt/gunyah/sysfs.c
> []
> > @@ -25,9 +25,24 @@ static ssize_t variant_show(struct kobject *kobj, struct kobj_attribute *attr, c
> >   }
> >   static struct kobj_attribute variant_attr = __ATTR_RO(variant);
> >   
> > +static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr, char *buffer)
> > +{
> > +	int len = 0;
> > +
> > +	if (GH_IDENTIFY_PARTITION_CSPACE(gunyah_api.flags))
> > +		len += sysfs_emit_at(buffer, len, "cspace ");
> > +	if (GH_IDENTIFY_MSGQUEUE(gunyah_api.flags))
> > +		len += sysfs_emit_at(buffer, len, "message-queue ");
> > +
> > +	len += sysfs_emit_at(buffer, len, "\n");
> > +	return len;
> > +}
>
> It's generally nicer to avoid unnecessary output spaces.
>
> Perhaps:
>
> {
> 	int len = 0;
>
> 	if (GH_IDENTIFY_PARTITION_CSPACE(gunyah_api.flags))
> 		len += sysfs_emit_at(buffer, len, "cspace");
> 	if (GH_IDENTIFY_MSGQUEUE(gunyah_api.flags)) {
> 		if (len)
> 			len += sysfs_emit_at(buffer, len, " ");
> 		len += sysfs_emit_at(buffer, len, "message-queue");
> 	}
>
> 	len += sysfs_emit_at(buffer, len, "\n");
>
> 	return len;
> }

that approach seems ok for 2 features, but imo doesn't scale for more.
I like the original code with one exception:

	if (GH_IDENTIFY_PARTITION_CSPACE(gunyah_api.flags))
		len += sysfs_emit_at(buffer, len, "cspace ");
	if (GH_IDENTIFY_MSGQUEUE(gunyah_api.flags))
		len += sysfs_emit_at(buffer, len, "message-queue ");

	/* overwrite last trailing space */
	if (len)
		len--;

	len += sysfs_emit_at(buffer, len, "\n");
	return len;