On 02/09/2016 09:53 PM, Bjorn Helgaas wrote:
> Hi Hannes,
>
> On Wed, Jan 13, 2016 at 12:25:33PM +0100, Hannes Reinecke wrote:
>> It is not always possible to determine the actual size of the VPD
>> data, so allow access to them if the size is set to '0'.
>>
>> Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
>> ---
>> drivers/pci/pci-sysfs.c | 20 ++++++++++++--------
>> 1 file changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
>> index eead54c..de327c3 100644
>> --- a/drivers/pci/pci-sysfs.c
>> +++ b/drivers/pci/pci-sysfs.c
>> @@ -772,10 +772,12 @@ static ssize_t read_vpd_attr(struct file *filp, struct kobject *kobj,
>> struct pci_dev *dev =
>> to_pci_dev(container_of(kobj, struct device, kobj));
>>
>> - if (off > bin_attr->size)
>> - count = 0;
>> - else if (count > bin_attr->size - off)
>> - count = bin_attr->size - off;
>> + if (bin_attr->size > 0) {
>> + if (off > bin_attr->size)
>> + count = 0;
>> + else if (count > bin_attr->size - off)
>> + count = bin_attr->size - off;
>> + }
>
> I'm trying to figure out why we do any of this checking here. It
> seems like we could do all of it in pci_read_vpd().
>
> Where is bin_attr->size set? I assume this is the "attr" allocated in
> pci_create_capabilities_sysfs(). I see that before your series, we
> set "attr->size = dev->vpd->len" there, but after patch 3/4 of your
> series, we set it to 0 there, and I don't see a place that sets it to
> anything else.
>
That is entirely correct.
One of the joys of sysfs binary attributes.
In general, sysfs binary attributes are allowed to have a size of
'0', but still can provide data when read.
The size of '0' is just an indicator for "I don't know how much data
I can provide, figure out yourself".
(Cf fs/sysfs/file.c:sysfs_kf_bin_read() for details here)
In our case we're not using that function, but rather our own
pci_read_vpd(), which always exposes a size.
So this patch just takes the same reasoning from
sysfs_kf_bin_read(), and sets the size to '0', as initially we
simply do _not_ know how much data will be provided.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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