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

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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;




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