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

Jeff Johnson
2022-10-02T23:31:14Z

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;