Re: [PATCH v7 03/12] PCI: liveupdate: Track incoming preserved PCI devices

[Alex Williamson <alex@shazbot.org>]

On Fri, 10 Jul 2026 21:26:06 +0000
David Matlack <dmatlack@google.com> wrote:

> @@ -298,6 +377,87 @@ void pci_liveupdate_unpreserve(struct pci_dev *dev)
>  }
>  EXPORT_SYMBOL_GPL(pci_liveupdate_unpreserve);
>  
> +static struct pci_flb_incoming *pci_liveupdate_flb_get_incoming(void)
> +{
> +	struct pci_flb_incoming *incoming = NULL;
> +	int ret;
> +
> +	ret = liveupdate_flb_get_incoming(&pci_liveupdate_flb, (void **)&incoming);
> +
> +	/* Live Update is not enabled. */
> +	if (ret == -EOPNOTSUPP)
> +		return NULL;
> +
> +	/* Live Update is enabled, but there is no incoming FLB data. */
> +	if (ret == -ENODATA)
> +		return NULL;
> +
> +	/*
> +	 * Live Update is enabled and there is incoming FLB data, but none of it
> +	 * matches pci_liveupdate_flb.compatible.
> +	 *
> +	 * This could mean that no PCI FLB data was passed by the previous
> +	 * kernel, but it could also mean the previous kernel used a different
> +	 * compatibility string (i.e. a different ABI).
> +	 */
> +	if (ret == -ENOENT) {
> +		pr_info_once("No incoming FLB matched %s\n", pci_liveupdate_flb.compatible);
> +		return NULL;
> +	}
> +
> +	/*
> +	 * There is incoming FLB data that matches pci_liveupdate_flb.compatible
> +	 * but it cannot be retrieved.
> +	 */
> +	if (ret)
> +		panic("Failed to retrieve incoming FLB data (%d)\n", ret);
> +
> +	return incoming;
> +}

I'm having trouble following the error escalation here.  What's
fundamentally the difference between FLB data being provided and not
compatible (subtle log message) versus FLB data being provided and
compatible but we cannot access it (panic!)?

Don't both suggest devices are running but we can't get their FLB data
to continue letting them run?

The errno interpretation is also slightly different than the comment
above liveupdate_flb_get_incoming():

 * Return: 0 on success, or a negative errno on failure. -ENODATA means no
 * incoming FLB data, -ENOENT means specific flb not found in the incoming
 * data, -ENODEV if the FLB's module is unloading, and -EOPNOTSUPP when
 * live update is disabled or not configured.

Thanks,
Alex