Re: [PATCH 2/2] pci: Expose offset, stride, and VF device ID via sysfs

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Oct 03, 2017 at 02:31:14PM -0500, Bjorn Helgaas wrote:
> On Fri, Sep 29, 2017 at 07:53:31AM +0000, Sironi, Filippo wrote:
> > 
> > Hi Bjorn,
> > 
> > > On 25. Sep 2017, at 20:55, Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > 
> > > Hi Filippo,
> > > 
> > > On Mon, Aug 28, 2017 at 03:38:50PM +0200, Filippo Sironi wrote:
> > >> +static ssize_t sriov_vf_did_show(struct device *dev,
> > >> +				 struct device_attribute *attr,
> > >> +				 char *buf)
> > >> +{
> > >> +	struct pci_dev *pdev = to_pci_dev(dev);
> > >> +
> > >> +	return sprintf(buf, "%x\n", pdev->sriov->vf_did);
> > >> +}
> > > 
> > > What does the vf_did part look like in sysfs?  Do we have a directory with
> > > both "device" and "vf_did" in it?  If so, why do we have both and do we
> > > need both?  Could we put the vf_did in the "device" file?
> > 
> > On my machine:
> > 
> > /sys/bus/pci/devices/0000:03:00.0# ls -l  # this is the PF
> > total 0
> > -rw-r--r-- 1 root root    4096 Sep 28 19:41 broken_parity_status
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 class
> > -rw-r--r-- 1 root root    4096 Sep 28 19:41 config
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 consistent_dma_mask_bits
> > -rw-r--r-- 1 root root    4096 Sep 28 19:41 d3cold_allowed
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 device
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 dma_mask_bits
> > lrwxrwxrwx 1 root root       0 Sep 28 19:41 driver -> ../../../../bus/pci/drivers/igb
> > -rw-r--r-- 1 root root    4096 Sep 28 19:41 driver_override
> > -rw-r--r-- 1 root root    4096 Sep 28 19:41 enable
> > lrwxrwxrwx 1 root root       0 Sep 28 19:41 firmware_node -> ../../../LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:4b/device:4c
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 irq
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 local_cpulist
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 local_cpus
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 modalias
> > -rw-r--r-- 1 root root    4096 Sep 28 19:41 msi_bus
> > drwxr-xr-x 2 root root       0 Sep 29 09:44 msi_irqs
> > drwxr-xr-x 3 root root       0 Sep 28 19:41 net
> > -rw-r--r-- 1 root root    4096 Sep 28 19:41 numa_node
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 offset  # this is new
> > drwxr-xr-x 2 root root       0 Sep 28 19:41 power
> > drwxr-xr-x 3 root root       0 Sep 28 19:41 ptp
> > --w--w---- 1 root root    4096 Sep 28 19:41 remove
> > --w--w---- 1 root root    4096 Sep 28 19:41 rescan
> > --w------- 1 root root    4096 Sep 28 19:41 reset
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 resource
> > -rw------- 1 root root  131072 Sep 28 19:41 resource0
> > -rw------- 1 root root 4194304 Sep 28 19:41 resource1
> > -rw------- 1 root root      32 Sep 28 19:41 resource2
> > -rw------- 1 root root   16384 Sep 28 19:41 resource3
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 revision
> > -rw-rw-r-- 1 root root    4096 Sep 29 09:44 sriov_numvfs
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 sriov_totalvfs
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 stride  # this is new
> > lrwxrwxrwx 1 root root       0 Sep 28 19:41 subsystem -> ../../../../bus/pci
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 subsystem_device
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 subsystem_vendor
> > -rw-r--r-- 1 root root    4096 Sep 28 19:41 uevent
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 vendor
> > -r--r--r-- 1 root root    4096 Sep 28 19:41 vf_did  # this is new
> > lrwxrwxrwx 1 root root       0 Sep 29 09:44 virtfn0 -> ../0000:03:10.0
> > 
> > nothing changes on for VFs.
> > Then:
> > 
> > /sys/bus/pci/devices/0000:03:00.0# cat device 
> > 0x10c9
> > 
> > /sys/bus/pci/devices/0000:03:00.0# cat vf_did
> > 0x10ca
> > 
> > Putting the VF device ID in the PF device file would be a change of
> > that we expose to userspace.  Something might break.
> 
> Oh, sorry, I misunderstood!  I was thinking that you were adding
> "vf_did" to the VF directory, not the PF directory.
> 
> Then I guess my only issue is that "vf_did" doesn't match the pattern
> of other names.  I think "virtfn_device" would give more of a hint and
> would match "device" and "subsystem_device".

I was going to just make this tweak myself, but realized I'd actually
propose these changes as well:

  offset -> sriov_offset
  stride -> sriov_stride
  vf_did -> virtfn_device (could be sriov_device as well)

and I can't really test it to make sure I get all the details right.
Can you update those and repost this?

Bjorn

> > vf_did provides a easy way to retrieve the VF device ID without reading
> > the PF config (looking up the SR-IOV capability and reading it) or without
> > enabling SR-IOV to read for example virtfn0/device.
> > 
> > Similar considerations (ease of access) apply to offset and stride.
> > 
> > 
> > >> static ssize_t sriov_drivers_autoprobe_show(struct device *dev,
> > >> 					    struct device_attribute *attr,
> > >> 					    char *buf)
> > >> @@ -676,6 +703,9 @@ static struct device_attribute sriov_totalvfs_attr = __ATTR_RO(sriov_totalvfs);
> > >> static struct device_attribute sriov_numvfs_attr =
> > >> 		__ATTR(sriov_numvfs, (S_IRUGO|S_IWUSR|S_IWGRP),
> > >> 		       sriov_numvfs_show, sriov_numvfs_store);
> > >> +static struct device_attribute sriov_offset_attr = __ATTR_RO(sriov_offset);
> > >> +static struct device_attribute sriov_stride_attr = __ATTR_RO(sriov_stride);
> > >> +static struct device_attribute sriov_vf_did_attr = __ATTR_RO(sriov_vf_did);
> > >> static struct device_attribute sriov_drivers_autoprobe_attr =
> > >> 		__ATTR(sriov_drivers_autoprobe, (S_IRUGO|S_IWUSR|S_IWGRP),
> > >> 		       sriov_drivers_autoprobe_show, sriov_drivers_autoprobe_store);
> > >> @@ -1744,6 +1774,9 @@ static struct attribute_group pci_dev_hp_attr_group = {
> > >> static struct attribute *sriov_dev_attrs[] = {
> > >> 	&sriov_totalvfs_attr.attr,
> > >> 	&sriov_numvfs_attr.attr,
> > >> +	&sriov_offset_attr.attr,
> > >> +	&sriov_stride_attr.attr,
> > >> +	&sriov_vf_did_attr.attr,
> > >> 	&sriov_drivers_autoprobe_attr.attr,
> > >> 	NULL,
> > >> };
> > >> -- 
> > >> 2.7.4
> > >> 
> > > 
> > 
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