On 02/24/2016 06:36 AM, Bjorn Helgaas wrote: > On Wed, Feb 24, 2016 at 05:48:33AM +0800, Hannes Reinecke wrote: >> On 02/23/2016 10:07 PM, Bjorn Helgaas wrote: >>> Hi Hannes, >>> >>> Thanks for taking a look at the rest of these. >>> >>> On Mon, Feb 22, 2016 at 06:46:23PM -0600, Bjorn Helgaas wrote: >>>> Hi Hannes, >>>> >>>> This is a revision of your v3 series: >>>> http://lkml.kernel.org/r/1455525722-122040-1-git-send-email-hare@xxxxxxx >>>> >>>> Here's the description from your v3 posting: >>>> >>>> the current PCI VPD page access assumes that the entire possible VPD >>>> data is readable. However, the spec only guarantees a VPD data up to >>>> the 'end' marker, with everything beyond that being undefined. >>>> This causes a system lockup on certain devices. >>>> >>>> With this patch we always set the VPD sysfs attribute size to '0', and >>>> calculate the available VPD size on the first access. >>>> If no valid data can be read an I/O error is returned. >>> >>> Just to see if I have this right: the VPD file size in sysfs will >>> always appear as zero, regardless of whether it has been read or >>> written, right? I don't think the user-visible size should change. >>> >> That is correct. >> As the actual size is evaluated on the first access, we don't have it >> available when creating the sysfs attribute itself. >> And when using the nominal size of 32k some bright program might try to >> jump to somewhere in the middle of the data, which will make calculating >> the validity of this horribly complex. >> Setting it to '0' is an easy way of avoiding this kinda games. >> >> So yes, there will be a user-visible change, but it shouldn't affect the >> programs accessing this attribute. >> lspci works happily with these changes > > What is the user-visible change? Here's what I'm thinking. If we do > this: > > ls -l /sys/.../vpd > dd if=/sys/.../vpd bs=1 count=1 > ls -l /sys/.../vpd > > Do we see different sizes from the two "ls" invocations? My thought > is that we should see '0' both times, because I don't really think > that output should change depending on previous actions of this user > or other users. > Originally we have: # ls -l 0000:07:00.0/vpd -rw------- 1 root root 32768 Feb 24 01:29 0000:07:00.0/vpd and with this patchset we have: # ls -l 0000:07:00.0/vpd -rw------- 1 root root 0 Feb 24 01:29 0000:07:00.0/vpd So only programs doing a 'stat' on the device node will see a difference. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
