linux-kernel - Re: [PATCH v5 3/8] char: rpmb: add device attributes

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Date:   Wed, 31 Aug 2016 12:56:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tomas Winkler <tomas.winkler@...el.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Vinayak Holikatti <vinholikatti@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Michael Ryleev <gmar@...gle.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Christoph Hellwig <hch@....de>,
        Yaniv Gardi <ygardi@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-scsi@...r.kernel.org
Subject: Re: [PATCH v5 3/8] char: rpmb: add device attributes

On Mon, Jul 18, 2016 at 11:27:48PM +0300, Tomas Winkler wrote:
> Add attribute type that displays underlay storage type technology
> EMMC, UFS, and attribute id, that displays underlay storage device id.
> For EMMC this would be content of CID and for UFS serial number from
> the device descriptor.
> 
> 
> Signed-off-by: Tomas Winkler <tomas.winkler@...el.com>
> ---
> V2: resend
> V3: set kernel version to 4.7
> V4: update target date to Maj
> V5: adjust date and kernel version
>  Documentation/ABI/testing/sysfs-class-rpmb | 24 ++++++++++++
>  drivers/char/rpmb/core.c                   | 63 ++++++++++++++++++++++++++++++
>  2 files changed, 87 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-rpmb b/Documentation/ABI/testing/sysfs-class-rpmb
> index 3ffcd2d1f683..7ca97d86bd97 100644
> --- a/Documentation/ABI/testing/sysfs-class-rpmb
> +++ b/Documentation/ABI/testing/sysfs-class-rpmb
> @@ -18,3 +18,27 @@ Contact:	Tomas Winkler <tomas.winkler@...el.com>
>  Description:
>  		The /sys/class/rpmb/rpmbN directory is created for
>  		each RPMB registered device
> +
> +What:		/sys/class/rpmb/rpmbN/id
> +Date:		Aug 2016
> +KernelVersion:	4.8
> +Contact:	Tomas Winkler <tomas.winkler@...el.com>
> +Description:
> +		The /sys/class/rpmb/rpmbN/id file contains device id
> +		in a binary form

Oops, missed that you added these in a later patch, sorry about comment
on patch 2.

binary attribute?  Why?

> +
> +What:		/sys/class/rpmb/rpmbN/type
> +Date:		Aug 2016
> +KernelVersion:	4.8
> +Contact:	Tomas Winkler <tomas.winkler@...el.com>
> +Description:
> +		The /sys/class/rpmb/rpmbN/type file contains device
> +		underlay storage type technology: EMMC, UFS
> +

What is this used for?

> +What:		/sys/class/rpmb/rpmbN/reliable_wr_cnt
> +Date:		Aug 2016
> +KernelVersion:	4.8
> +Contact:	Tomas Winkler <tomas.winkler@...el.com>
> +Description:
> +		The /sys/class/rpmb/rpmbN/reliable_wr_cnt file contains
> +		number of blocks that can be written in a single request

Why is this needed?  Shouldn't the normal block device export this type
of information?


> diff --git a/drivers/char/rpmb/core.c b/drivers/char/rpmb/core.c
> index ff10cbb7b644..63271c7ed072 100644
> --- a/drivers/char/rpmb/core.c
> +++ b/drivers/char/rpmb/core.c
> @@ -308,6 +308,67 @@ struct rpmb_dev *rpmb_dev_find_by_device(struct device *parent)
>  }
>  EXPORT_SYMBOL_GPL(rpmb_dev_find_by_device);
>  
> +static ssize_t type_show(struct device *dev,
> +			 struct device_attribute *attr, char *buf)
> +{
> +	struct rpmb_dev *rdev = to_rpmb_dev(dev);
> +	ssize_t ret;
> +
> +	switch (rdev->ops->type) {
> +	case RPMB_TYPE_EMMC:
> +		ret = scnprintf(buf, PAGE_SIZE, "EMMC\n");

It's a sysfs file, no need for scnprintf() crap, just use sprintf()
please.

> +		break;

And the code can be made smaller by just doing:
		return sprintf(buf, "EMMC\n");

:)

> +	case RPMB_TYPE_UFS:
> +		ret = scnprintf(buf, PAGE_SIZE, "UFS\n");
> +		break;
> +	default:
> +		ret = scnprintf(buf, PAGE_SIZE, "UNKNOWN\n");
> +		break;
> +	}
> +
> +	return ret;
> +}
> +static DEVICE_ATTR_RO(type);
> +
> +static ssize_t id_show(struct device *dev,
> +		       struct device_attribute *attr, char *buf)
> +{
> +	struct rpmb_dev *rdev = to_rpmb_dev(dev);
> +	size_t sz = min_t(size_t, rdev->ops->dev_id_len, PAGE_SIZE);
> +
> +	if (!rdev->ops->dev_id)
> +		return 0;
> +
> +	memcpy(buf, rdev->ops->dev_id, sz);
>

Hm, no.  That's not how a binary attribute works.  If you want a binary
attribute, use that type, don't put binary data in a "normal" sysfs
file.

> +	return sz;
> +}
> +static DEVICE_ATTR_RO(id);
> +
> +static ssize_t reliable_wr_cnt_show(struct device *dev,
> +				    struct device_attribute *attr, char *buf)
> +{
> +	struct rpmb_dev *rdev = to_rpmb_dev(dev);
> +
> +	return scnprintf(buf, PAGE_SIZE, "%u\n", rdev->ops->reliable_wr_cnt);
> +}
> +static DEVICE_ATTR_RO(reliable_wr_cnt);
> +
> +static struct attribute *rpmb_attrs[] = {
> +	&dev_attr_type.attr,
> +	&dev_attr_id.attr,
> +	&dev_attr_reliable_wr_cnt.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group rpmb_attr_group = {
> +	.attrs = rpmb_attrs,
> +};
> +
> +static const struct attribute_group *rpmb_attr_groups[] = {
> +	&rpmb_attr_group,
> +	NULL
> +};
> +
>  /**
>   * rpmb_dev_unregister - unregister RPMB partition from the RPMB subsystem
>   *
> @@ -377,6 +438,8 @@ struct rpmb_dev *rpmb_dev_register(struct device *dev,
>  	dev_set_name(&rdev->dev, "rpmb%d", id);
>  	rdev->dev.class = &rpmb_class;
>  	rdev->dev.parent = dev;
> +	rdev->dev.groups = rpmb_attr_groups;

Nice job with the group, thanks for doing that.

greg k-h