linux-kernel - Re: [PATCH v3] PCI/DOE: Expose the DOE protocols via sysfs

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Date:   Sat, 12 Aug 2023 10:15:26 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Alistair Francis <alistair23@...il.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        Jonathan.Cameron@...wei.com, alex.williamson@...hat.com,
        christian.koenig@....com, kch@...dia.com,
        gregkh@...uxfoundation.org, logang@...tatee.com,
        linux-kernel@...r.kernel.org,
        Alistair Francis <alistair.francis@....com>
Subject: Re: [PATCH v3] PCI/DOE: Expose the DOE protocols via sysfs

On Thu, Aug 10, 2023 at 11:34:11AM -0400, Alistair Francis wrote:
> On Thu, Aug 10, 2023 at 3:34???AM Lukas Wunner <lukas@...ner.de> wrote:
> > On Wed, Aug 09, 2023 at 07:28:51PM -0400, Alistair Francis wrote:
> > > --- a/drivers/pci/pci-sysfs.c
> > > +++ b/drivers/pci/pci-sysfs.c
> > > @@ -1226,6 +1227,12 @@ static int pci_create_resource_files(struct pci_dev *pdev)
> > >       int i;
> > >       int retval;
> > >
> > > +#ifdef CONFIG_PCI_DOE
> > > +     retval = doe_sysfs_init(pdev);
> > > +     if (retval)
> > > +             return retval;
> > > +#endif
> > > +
> >
> > The preferred way to expose PCI sysfs attributes nowadays is to add them
> > to pci_dev_attr_groups[] and use the ->is_visible callback to check
> > whether they're applicable to a particular pci_dev.  The alternative
> > via pci_create_resource_files() has race conditions which I think
> > still haven't been fixed. Bjorn recommended the ->is_visible approach
> > in response to the most recent attempt to fix the race:
> >
> > https://lore.kernel.org/linux-pci/20230427161458.GA249886@bhelgaas/
> 
> The is_visible doen't seem to work in this case.
> 
> AFAIK is_visible only applies to the attributes under the group. Which
> means that every PCIe device will see a `doe_protos` directory, no
> matter if DOE is supported.

internal_create_group() in fs/sysfs/group.c does this:

	if (grp->name) {
			...
			kn = kernfs_create_dir_ns(kobj->sd, grp->name, ...

So I'm under the impression that if you set the ->name member of
struct attribute_group, the attributes in that group appear under
a directory of that name.

In fact, the kernel-doc for struct attribute_group claims as much:

 * struct attribute_group - data structure used to declare an attribute group.
 * @name:	Optional: Attribute group name
 *		If specified, the attribute group will be created in
 *		a new subdirectory with this name.

So I don't quite understand why you think that "every PCIe device will
see a `doe_protos` directory, no matter if DOE is supported"?

Am I missing something?

Thanks,

Lukas