How does lspci find out physical slot number of a PCI(E) device?

Question

lspci is capable to show physical slot number in the verbose presentation:

I'd like to find out how it does it. I am going to apply this method in the driver that I would like to modify, so it would enumerate the devices (with the same ID) and disambiguate the device files according to physical slot. Like /dev/device_physslot . The driver will run on Ubuntu 18

I tried to dig in the source code. I found the relevant line 775 in https://github.com/pciutils/pciutils/blob/master/lspci.c:

if (p->phy_slot)
    printf("\tPhysical Slot: %s\n", p->phy_slot);

p is struct pci_dev. That had been quite confusing because standard linux/pci.h does not have field phy_slot until I figured out that is their own (re)definition

The structure is filled by the function

int
pci_fill_info_v38(struct pci_dev *d, int flags)
{
  unsigned int uflags = flags;
  if (uflags & PCI_FILL_RESCAN)
    {
      uflags &= ~PCI_FILL_RESCAN;
      pci_reset_properties(d);
    }
  if (uflags & ~d->known_fields)
    d->methods->fill_info(d, uflags);
  return d->known_fields;
}

fill_info is a function pointer defined in https://github.com/pciutils/pciutils/blob/master/lib/internal.h (line 44)

And that's where I lost track.

stark · Answer 1 · 2022-02-25T21:13:24.797

1

If you run dmidecode it will show the stored platform information, which will tell you the mapping of physical slots to PCIe address. For example:

Handle 0x001D, DMI type 9, 17 bytes
System Slot Information
    Designation: J6B1
    Type: x1 PCI Express
    Current Usage: In Use
    Length: Short
    ID: 1                      <== SLOT (starting at 0)
    Characteristics:
        3.3 V is provided
        Opening is shared
        PME signal is supported
    Bus Address: 0000:00:1c.3    <== PCI BUS ADDRESS

Proogrammatic list of slots:

sudo dmidecode -t 9 |awk '/ID:/ {id=$2} /Bus Address/ {print "Slot",id+1,"PCIe",$3}'
Slot 1 PCIe 0000:00:01.0
Slot 2 PCIe 0000:00:1c.3
Slot 3 PCIe 0000:00:1c.4
Slot 4 PCIe 0000:00:1c.5
Slot 5 PCIe 0000:00:1c.6

edited Feb 25 '22 at 21:13

answered Feb 25 '22 at 20:35

stark

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Thanks, but I meant programatically, with C code – Andrey Pro Feb 25 '22 at 20:40
Just read and parse the DMI data, then. – stark Feb 25 '22 at 20:49
Sorry, that is not what I ask for. I extended the explanation of application, so you perhaps would be able to provide suitable answer – Andrey Pro Feb 26 '22 at 23:45

score 1 · Accepted Answer · answered Mar 04 '22 at 19:45

After digging deeper in the source and succeeding to run lspci in the debugger (thanks to Netbeans) I found out that lspci uses sysfs to gather information. In particular /sys/bus/pci/slots/slot_num/address file contains the bus address of the slot. And that's what lspci uses to attribute slots to bus addresses in the function sysfs_fill_slots (in sysfs.c)

Unfortunately this method turns out to be unsuitable for my purposes, since it is not possible to perform file I/O from kernel module.

How does lspci find out physical slot number of a PCI(E) device?

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