Re: [PATCH 2/2] PCI/VPD: Improve handling binary sysfs attribute

[Heiner Kallweit <hkallweit1@gmail.com>]

On 03.02.2021 01:09, Bjorn Helgaas wrote:
> On Thu, Jan 07, 2021 at 10:48:55PM +0100, Heiner Kallweit wrote:
>> Since 104daa71b396 ("PCI: Determine actual VPD size on first access")
>> there's nothing that keeps us from using a static attribute.
>> This allows to significantly simplify the code.
> 
> I love this!  A few comments below.
> 
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>>  drivers/pci/vpd.c | 42 +++++++++++-------------------------------
>>  1 file changed, 11 insertions(+), 31 deletions(-)
>>
>> diff --git a/drivers/pci/vpd.c b/drivers/pci/vpd.c
>> index a3fd09105..9ef8f400e 100644
>> --- a/drivers/pci/vpd.c
>> +++ b/drivers/pci/vpd.c
>> @@ -21,7 +21,6 @@ struct pci_vpd_ops {
>>  
>>  struct pci_vpd {
>>  	const struct pci_vpd_ops *ops;
>> -	struct bin_attribute *attr;	/* Descriptor for sysfs VPD entry */
>>  	struct mutex	lock;
>>  	unsigned int	len;
>>  	u16		flag;
>> @@ -397,57 +396,38 @@ void pci_vpd_release(struct pci_dev *dev)
>>  	kfree(dev->vpd);
>>  }
>>  
>> -static ssize_t read_vpd_attr(struct file *filp, struct kobject *kobj,
>> -			     struct bin_attribute *bin_attr, char *buf,
>> -			     loff_t off, size_t count)
>> +static ssize_t vpd_read(struct file *filp, struct kobject *kobj,
>> +			struct bin_attribute *bin_attr, char *buf,
>> +			loff_t off, size_t count)
>>  {
>>  	struct pci_dev *dev = to_pci_dev(kobj_to_dev(kobj));
>>  
>>  	return pci_read_vpd(dev, off, count, buf);
>>  }
>>  
>> -static ssize_t write_vpd_attr(struct file *filp, struct kobject *kobj,
>> -			      struct bin_attribute *bin_attr, char *buf,
>> -			      loff_t off, size_t count)
>> +static ssize_t vpd_write(struct file *filp, struct kobject *kobj,
>> +			 struct bin_attribute *bin_attr, char *buf,
>> +			 loff_t off, size_t count)
>>  {
>>  	struct pci_dev *dev = to_pci_dev(kobj_to_dev(kobj));
>>  
>>  	return pci_write_vpd(dev, off, count, buf);
>>  }
>>  
>> +static const BIN_ATTR_RW(vpd, 0);
> 
> Wow, I'm surprised that there are only 50ish uses of BIN_ATTR_*():
> s390/crypto, w1/slaves/..., and a few other places.  It always makes
> me wonder when we're one of a small number of callers.  Seems OK
> though.
> 
>>  void pcie_vpd_create_sysfs_dev_files(struct pci_dev *dev)
>>  {
>> -	int retval;
>> -	struct bin_attribute *attr;
>> -
>>  	if (!dev->vpd)
>>  		return;
>>  
>> -	attr = kzalloc(sizeof(*attr), GFP_ATOMIC);
>> -	if (!attr)
>> -		return;
>> -
>> -	sysfs_bin_attr_init(attr);
>> -	attr->size = 0;
>> -	attr->attr.name = "vpd";
>> -	attr->attr.mode = S_IRUSR | S_IWUSR;
>> -	attr->read = read_vpd_attr;
>> -	attr->write = write_vpd_attr;
>> -	retval = sysfs_create_bin_file(&dev->dev.kobj, attr);
>> -	if (retval) {
>> -		kfree(attr);
>> -		return;
>> -	}
>> -
>> -	dev->vpd->attr = attr;
> 
> Above is awesome.  Also maybe confirms that we could remove the
> "attr->size = 0" assignment in the previous patch?
> 
Technically this assignment has never been needed, because the
attribute memory is kzalloc'ed. But it makes clear to the
reader that sysfs code isn't supposed to do any length checks.

>> +	if (sysfs_create_bin_file(&dev->dev.kobj, &bin_attr_vpd))
>> +		pci_warn(dev, "can't create VPD sysfs file\n");
> 
> Not sure we need this.  Can't we use the .is_visible() thing and an
> attribute group to get rid of the explicit sysfs_create_bin_file()?
> 
Nice. Let me do this, I'll send a v2 of the series.

>>  }
>>  
>>  void pcie_vpd_remove_sysfs_dev_files(struct pci_dev *dev)
>>  {
>> -	if (dev->vpd && dev->vpd->attr) {
>> -		sysfs_remove_bin_file(&dev->dev.kobj, dev->vpd->attr);
>> -		kfree(dev->vpd->attr);
>> -	}
>> +	sysfs_remove_bin_file(&dev->dev.kobj, &bin_attr_vpd);
>>  }
>>  
>>  int pci_vpd_find_tag(const u8 *buf, unsigned int off, unsigned int len, u8 rdt)
>> -- 
>> 2.30.0
>>
>>