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

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Message-ID: <CAKmqyKPx9Oi-ZF0grdUzkHi5BjyyNQZ2r30vgShR6cOY9xZ9YQ@mail.gmail.com>
Date:   Tue, 15 Aug 2023 09:44:32 -0400
From:   Alistair Francis <alistair23@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Lukas Wunner <lukas@...ner.de>, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, Jonathan.Cameron@...wei.com,
        alex.williamson@...hat.com, christian.koenig@....com,
        kch@...dia.com, 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 Sat, Aug 12, 2023 at 4:26 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Sat, Aug 12, 2023 at 10:15:26AM +0200, Lukas Wunner wrote:
> > 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?
>
> I think the issue might be that the directory will be created even if no
> attributes are present in it due to the is_visable() check not returning
> any valid files?

Yes, that's what I'm seeing. I see the directory for all PCIe devices

This is a WIP that I had:
https://github.com/alistair23/linux/commit/61925cd174c31386eaa7e51e3a1be606b38f847c

>
> If so, I had a patch somewhere around here where I was trying to fix
> that up:
>         https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git/commit/?h=debugfs_cleanup&id=f670945dfbaf353fe068544c31e3fa45575da5b5
> but it didn't seem to work properly and kept crashing.  I didn't spend
> much time on looking into it, but if this is an issue, I can work on
> fixing this properly.

That patch sounds like it would fix the issue of empty directories
that I'm seeing. Do you mind fixing it up properly?

Then I just need to address the race condition and we can switch to
using .is_visible()

Alistair

>
> thanks,
>
> greg k-h