Re: [PATCH v4 02/11] PCI: liveupdate: Track outgoing preserved PCI devices

[Vipin Sharma <vipinsh@google.com>]

On Thu, Apr 23, 2026 at 09:23:06PM +0000, David Matlack wrote:
> +int pci_liveupdate_preserve(struct pci_dev *dev)
> +{
> +	struct pci_ser *ser;
> +	int i, ret;
> +
> +	guard(mutex)(&pci_flb_outgoing_lock);
> +
> +	ret = liveupdate_flb_get_outgoing(&pci_liveupdate_flb, (void **)&ser);
> +	if (ret)
> +		return ret;
> +
> +	if (!ser)
> +		return -ENOENT;
> +
> +	if (dev->is_virtfn)
> +		return -EINVAL;
> +
> +	if (dev->liveupdate_outgoing)
> +		return -EBUSY;
> +
> +	if (ser->nr_devices == ser->max_nr_devices)
> +		return -ENOSPC;
> +
> +	for (i = 0; i < ser->max_nr_devices; i++) {
> +		/*
> +		 * Start searching at index ser->nr_devices. This should result
> +		 * in a constant time search under expected conditions (devices
> +		 * are not getting unpreserved).
> +		 */
> +		int index = (ser->nr_devices + i) % ser->max_nr_devices;
> +		struct pci_dev_ser *dev_ser = &ser->devices[index];
> +
> +		if (dev_ser->refcount)
> +			continue;
> +
> +		pci_info(dev, "Device will be preserved across next Live Update\n");
> +		ser->nr_devices++;
> +
> +		dev_ser->domain = pci_domain_nr(dev->bus);
> +		dev_ser->bdf = pci_dev_id(dev);
> +		dev_ser->refcount = 1;
> +
> +		dev->liveupdate_outgoing = dev_ser;
> +		return 0;
> +	}
> +
> +	return -ENOSPC;

Since it is executing under a mutex, and we already failed
'if (ser->nr_devices == ser->max_nr_devices) check above, will we ever reach
here and return -ENOSPC?

> diff --git a/include/linux/kho/abi/pci.h b/include/linux/kho/abi/pci.h
> index 5c0e92588c00..5b4c8d9e462c 100644
> --- a/include/linux/kho/abi/pci.h
> +++ b/include/linux/kho/abi/pci.h
> @@ -23,19 +23,20 @@
>   * incrementing the version number in the PCI_LUO_FLB_COMPATIBLE string.
>   */
>  
> -#define PCI_LUO_FLB_COMPATIBLE "pci-v1"
> +#define PCI_LUO_FLB_COMPATIBLE "pci-v2"

Just curious, why did we change the version here? It's not like just
previous patch is working enough to perform a live update. As the config
is experimental, can't we just keep it PCI-v1 for the whole series?

>