netdev - Re: [PATCH mlx5-next v6 1/4] PCI: Add sysfs callback to allow MSI-X table size change of SR-IOV VFs

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Date:   Tue, 16 Feb 2021 16:37:26 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     Leon Romanovsky <leon@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jakub Kicinski <kuba@...nel.org>, <linux-pci@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, <netdev@...r.kernel.org>,
        Don Dutile <ddutile@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH mlx5-next v6 1/4] PCI: Add sysfs callback to allow MSI-X
 table size change of SR-IOV VFs

On Tue, Feb 16, 2021 at 10:12:12AM -0600, Bjorn Helgaas wrote:
> > >
> > > But I still don't like the fact that we're calling
> > > sysfs_create_files() and sysfs_remove_files() directly.  It makes
> > > complication and opportunities for errors.
> > 
> > It is not different from any other code that we have in the kernel.
> 
> It *is* different.  There is a general rule that drivers should not
> call sysfs_* [1].  The PCI core is arguably not a "driver," but it is
> still true that callers of sysfs_create_files() are very special, and
> I'd prefer not to add another one.

I think the point of [1] is people should be setting up their sysfs in
the struct device attribute groups/etc before doing device_add() and
allowing the driver core to handle everything. This can be done in
a lot of cases, eg we have examples of building a dynamic list of
attributes

In other cases, calling wrappers like device_create_file() introduces
a bit more type safety, so adding a device_create_files() would be
trivial enough

Other places in PCI are using syfs_create_group() (and there are over
400 calls to this function in all sorts of device drivers):

drivers/pci/msi.c:      ret = sysfs_create_groups(&pdev->dev.kobj, msi_irq_groups);
drivers/pci/p2pdma.c:   error = sysfs_create_group(&pdev->dev.kobj, &p2pmem_group);
drivers/pci/pci-label.c:        return sysfs_create_group(&pdev->dev.kobj, &smbios_attr_group);
drivers/pci/pci-label.c:        return sysfs_create_group(&pdev->dev.kobj, &acpi_attr_group);

For post-driver_add() stuff, maybe this should do the same, a
"srio_vf/" group?

And a minor cleanup would change these to use device_create_bin_file():

drivers/pci/pci-sysfs.c:        retval = sysfs_create_bin_file(&pdev->dev.kobj, res_attr);
drivers/pci/pci-sysfs.c:                retval = sysfs_create_bin_file(&pdev->dev.kobj, &pcie_config_attr);
drivers/pci/pci-sysfs.c:                retval = sysfs_create_bin_file(&pdev->dev.kobj, &pci_config_attr);
drivers/pci/pci-sysfs.c:                retval = sysfs_create_bin_file(&pdev->dev.kobj, attr);
drivers/pci/vpd.c:      retval = sysfs_create_bin_file(&dev->dev.kobj, attr);

I haven't worked out why pci_create_firmware_label_files() and all of
this needs to be after device_add() though.. Would be slick to put
that in the normal attribute list - we've got some examples of dynamic
pre-device_add() attribute lists in the tree (eg tpm, rdma) that work
nicely.

Jason