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

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Date:   Thu, 10 Aug 2023 09:44:44 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Alistair Francis <alistair23@...il.com>, 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 Thu, Aug 10, 2023 at 07:05:12AM +0200, Greg KH wrote:
> On Wed, Aug 09, 2023 at 07:28:51PM -0400, Alistair Francis wrote:
> > v3:
> >  - Expose each DOE feature as a separate file
> 
> But you don't actually have anything in the sysfs files, why not?

He wants to expose a list of supported protocols.

He first exposed the list in a single attribute, separated by newlines.
Which made sense because it allows users to grep for a specific protocol.

You told him not to expose multiple values in a single attribute.
So he's exposing the available protocols each in an empty file.
The file name contains the protocol.

You got what you asked for. ;)

> > --- a/drivers/pci/doe.c
> > +++ b/drivers/pci/doe.c
> > @@ -56,6 +56,10 @@ struct pci_doe_mb {
> >  	wait_queue_head_t wq;
> >  	struct workqueue_struct *work_queue;
> >  	unsigned long flags;
> > +
> > +#ifdef CONFIG_SYSFS
> > +	struct device_attribute *sysfs_attrs;
> > +#endif
> 
> Please don't put #ifdefs in .c files if you can prevent it.  I think
> this will work just fine if you don't have the #ifdef.  And who would be
> using pci without sysfs?

People with space-constrained devices such as routers.

It is perfectly legal to compile a kernel with CONFIG_PCI=y and
CONFIG_SYSFS=n.

And it is reasonable not to include code in the kernel which has
specifically been deselected in the kernel config.

Thanks,

Lukas