linux-kernel - Re: [PATCH] Generic WorkQueue Engine (GenWQE) device driver (v4)

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Date:	Wed, 30 Oct 2013 10:44:03 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Frank Haverkamp <haver@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, arnd@...db.de,
	cody@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
	utz.bacher@...ibm.com, mmarek@...e.cz, rmallon@...il.com,
	jsvogt@...ibm.com, MIJUNG@...ibm.com, cascardo@...ux.vnet.ibm.com,
	michael@...ra.de, Frank Haverkamp <haver@...t.ibm.com>
Subject: Re: [PATCH] Generic WorkQueue Engine (GenWQE) device driver (v4)

On Wed, Oct 30, 2013 at 10:32:58AM +0100, Frank Haverkamp wrote:
> +/*
> + * Create device_attribute structures / params: name, mode, show, store
> + * additional flag if valid in VF
> + */
> +struct genwqe_dev_attrib {
> +	struct device_attribute att;	/* sysfs entry attributes */
> +	int vf;				/* may exist in VF or not */
> +};

Why do you need your own structure?  Use the is_visible() callback to
create or not, the individual attributes for a specific device, don't
roll your own logic for something the driver core already supports.

> +static struct genwqe_dev_attrib dev_attr_tab[] = {
> +	{__ATTR(tempsens,       S_IRUGO, show_card_tempsens, NULL), 0},
> +	{__ATTR(next_bitstream, (S_IRUGO | S_IWUSR),
> +		show_card_next_bitstream, store_card_next_bitstream), 0},
> +	{__ATTR(curr_bitstream, S_IRUGO, show_card_curr_bitstream, NULL), 0},
> +	{__ATTR(cpld_version,   S_IRUGO, show_cpld_version, NULL), 0},
> +	{__ATTR(base_clock,	S_IRUGO, show_card_base_clock, NULL), 0},
> +
> +	{__ATTR(driver,		S_IRUGO, show_card_driver, NULL), 1},
> +	{__ATTR(type,		S_IRUGO, show_card_type, NULL), 1},
> +	{__ATTR(version,	S_IRUGO, show_card_version, NULL), 1},
> +	{__ATTR(appid,		S_IRUGO, show_card_appid, NULL), 1},
> +	{__ATTR(status,		S_IRUGO, show_card_status, NULL), 1},
> +};
> +
> +/**
> + * create_card_sysfs() - Setup sysfs entries of the card device
> + *
> + * VFs have restricted mmio capabilities, so not all sysfs entries
> + * are allowed in VFs.
> + */
> +int create_card_sysfs(struct genwqe_dev *cd)
> +{
> +	int rc, priv;
> +	unsigned int i;
> +
> +	priv = genwqe_is_privileged(cd);
> +	for (i = 0; i < ARRAY_SIZE(dev_attr_tab); i++) {
> +		struct genwqe_dev_attrib *dev_attr = &dev_attr_tab[i];
> +		if (dev_attr->vf || priv) {
> +			rc = device_create_file(cd->dev, &dev_attr->att);

No, you just raced with userspace, creating the sysfs files _after_ it
was told to userspace that the driver was bound to the device.

Please use the attribute groups for this driver to have the driver core
create the files before it it told to userspace.

Also, instead of using __ATTR(), please use DEVICE_ATTR_RO(), it makes
things easier to audit and saves me from having to change it later on
(I'm doing a tree-wide change of this type of thing...)

thanks,

greg k-h
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