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

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Message-ID: <3c02aad6d8bde70964b403a3cb8004de969becc6.camel@perches.com>
Date:   Thu, 29 Sep 2022 00:36:50 -0700
From:   Joe Perches <joe@...ches.com>
To:     Elliot Berman <quic_eberman@...cinc.com>,
        Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Murali Nalajala <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 10/14] gunyah: sysfs: Add node to describe supported
 features

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;
}