Re: [PATCH] PCI: hv: support reporting serial number as slot information

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Tue, Jun 12, 2018 at 09:40:37AM -0700, Stephen Hemminger wrote:
> The Hyper-V host API for PCI provides a unique "serial number" which
> can be used as the basis for sysfs PCI slot table. This can be useful
> for cases where userspace wants to find the PCI device based on
> serial number.
> 
> When an SR-IOV NIC is added, the host sends an attach message
> with a serial number. The kernel doesn't use the serial number, but
> it is useful when doing the same thing in a userspace driver such
> as the DPDK. By having /sys/bus/pci/slots/N it provides a direct
> way to find the matching PCI device.
> 
> There may be some cases where the serial number is not unique such
> as when using GPU's. But the PCI slot infrastructure will handle
> that.
> 
> This also shortens the network device names generated by
> systemd/udev. The new names use slot (ens2) rather than
> PCI address (enP2p0s2).

Hi Stephen,

I wanted to apply this patch but wanted to make sure all HV
maintainers are in agreement first since this looks like
a significant user-space ABI change.

I would also ask Bjorn's opinion on this since he has more
insights into the slot interface history.

Thanks,
Lorenzo

> Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
> ---
> v2
>   - retarget for current filenames in PCI next
>   - remove debug log message
> 
>  drivers/pci/controller/pci-hyperv.c | 30 +++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 6cc5036ac83c..4e3575716ced 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -88,6 +88,8 @@ static enum pci_protocol_version_t pci_protocol_version;
>  
>  #define STATUS_REVISION_MISMATCH 0xC0000059
>  
> +#define SLOT_NAME_SIZE 21
> +
>  /*
>   * Message Types
>   */
> @@ -493,6 +495,7 @@ struct hv_pci_dev {
>  	struct list_head list_entry;
>  	refcount_t refs;
>  	enum hv_pcichild_state state;
> +	struct pci_slot *pci_slot;
>  	struct pci_function_description desc;
>  	bool reported_missing;
>  	struct hv_pcibus_device *hbus;
> @@ -1454,6 +1457,28 @@ static void prepopulate_bars(struct hv_pcibus_device *hbus)
>  	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
>  }
>  
> +static void hv_pci_assign_slots(struct hv_pcibus_device *hbus)
> +{
> +	struct hv_pci_dev *hpdev;
> +	char name[SLOT_NAME_SIZE];
> +	unsigned long flags;
> +	int slot_nr;
> +
> +	spin_lock_irqsave(&hbus->device_list_lock, flags);
> +	list_for_each_entry(hpdev, &hbus->children, list_entry) {
> +		if (hpdev->pci_slot)
> +			continue;
> +
> +		slot_nr = PCI_SLOT(wslot_to_devfn(hpdev->desc.win_slot.slot));
> +		snprintf(name, SLOT_NAME_SIZE, "%u", hpdev->desc.ser);
> +		hpdev->pci_slot = pci_create_slot(hbus->pci_bus, slot_nr,
> +					  name, NULL);
> +		if (!hpdev->pci_slot)
> +			pr_warn("pci_create slot %s failed\n", name);
> +	}
> +	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
> +}
> +
>  /**
>   * create_root_hv_pci_bus() - Expose a new root PCI bus
>   * @hbus:	Root PCI bus, as understood by this driver
> @@ -1477,6 +1502,7 @@ static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus)
>  	pci_lock_rescan_remove();
>  	pci_scan_child_bus(hbus->pci_bus);
>  	pci_bus_assign_resources(hbus->pci_bus);
> +	hv_pci_assign_slots(hbus);
>  	pci_bus_add_devices(hbus->pci_bus);
>  	pci_unlock_rescan_remove();
>  	hbus->state = hv_pcibus_installed;
> @@ -1739,6 +1765,7 @@ static void pci_devices_present_work(struct work_struct *work)
>  		 */
>  		pci_lock_rescan_remove();
>  		pci_scan_child_bus(hbus->pci_bus);
> +		hv_pci_assign_slots(hbus);
>  		pci_unlock_rescan_remove();
>  		break;
>  
> @@ -1855,6 +1882,9 @@ static void hv_eject_device_work(struct work_struct *work)
>  	list_del(&hpdev->list_entry);
>  	spin_unlock_irqrestore(&hpdev->hbus->device_list_lock, flags);
>  
> +	if (hpdev->pci_slot)
> +		pci_destroy_slot(hpdev->pci_slot);
> +
>  	memset(&ctxt, 0, sizeof(ctxt));
>  	ejct_pkt = (struct pci_eject_response *)&ctxt.pkt.message;
>  	ejct_pkt->message_type.type = PCI_EJECTION_COMPLETE;
> -- 
> 2.17.1
>