On Thu, Feb 18, 2021 at 12:15:51PM +0200, Leon Romanovsky wrote: > On Wed, Feb 17, 2021 at 12:02:39PM -0600, Bjorn Helgaas wrote: > > [+cc Greg in case he wants to chime in on the sysfs discussion. > > TL;DR: we're trying to add/remove sysfs files when a PCI driver that > > supports certain callbacks binds or unbinds; series at > > https://lore.kernel.org/r/20210209133445.700225-1-leon@xxxxxxxxxx] > > > > On Tue, Feb 16, 2021 at 09:58:25PM +0200, Leon Romanovsky wrote: > > > On Tue, Feb 16, 2021 at 10:12:12AM -0600, Bjorn Helgaas wrote: > > > > On Tue, Feb 16, 2021 at 09:33:44AM +0200, Leon Romanovsky wrote: > > > > > On Mon, Feb 15, 2021 at 03:01:06PM -0600, Bjorn Helgaas wrote: > > > > > > On Tue, Feb 09, 2021 at 03:34:42PM +0200, Leon Romanovsky wrote: > > > > > > > From: Leon Romanovsky <leonro@xxxxxxxxxx> > > > > > > > > > +int pci_enable_vf_overlay(struct pci_dev *dev) > > > > > > > +{ > > > > > > > + struct pci_dev *virtfn; > > > > > > > + int id, ret; > > > > > > > + > > > > > > > + if (!dev->is_physfn || !dev->sriov->num_VFs) > > > > > > > + return 0; > > > > > > > + > > > > > > > + ret = sysfs_create_files(&dev->dev.kobj, sriov_pf_dev_attrs); > > > > > > > > > > > > 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. > > > > > > PCI for me is a bus, and bus is the right place to manage sysfs. > > > But it doesn't matter, we understand each other positions. > > > > > > > > Let's be concrete, can you point to the errors in this code that I > > > > > should fix? > > > > > > > > I'm not saying there are current errors; I'm saying the additional > > > > code makes errors possible in future code. For example, we hope that > > > > other drivers can use these sysfs interfaces, and it's possible they > > > > may not call pci_enable_vf_overlay() or pci_disable_vfs_overlay() > > > > correctly. > > > > > > If not, we will fix, we just need is to ensure that sysfs name won't > > > change, everything else is easy to change. > > > > > > > Or there may be races in device addition/removal. We have current > > > > issues in this area, e.g., [2], and they're fairly subtle. I'm not > > > > saying your patches have these issues; only that extra code makes more > > > > chances for mistakes and it's more work to validate it. > > > > > > > > > > I don't see the advantage of creating these files only when > > > > > > the PF driver supports this. The management tools have to > > > > > > deal with sriov_vf_total_msix == 0 and sriov_vf_msix_count == > > > > > > 0 anyway. Having the sysfs files not be present at all might > > > > > > be slightly prettier to the person running "ls", but I'm not > > > > > > sure the code complication is worth that. > > > > > > > > > > It is more than "ls", right now sriov_numvfs is visible without > > > > > relation to the driver, even if driver doesn't implement > > > > > ".sriov_configure", which IMHO bad. We didn't want to repeat. > > > > > > > > > > Right now, we have many devices that supports SR-IOV, but small > > > > > amount of them are capable to rewrite their VF MSI-X table siz. > > > > > We don't want "to punish" and clatter their sysfs. > > > > > > > > I agree, it's clutter, but at least it's just cosmetic clutter > > > > (but I'm willing to hear discussion about why it's more than > > > > cosmetic; see below). > > > > > > It is more than cosmetic and IMHO it is related to the driver role. > > > This feature is advertised, managed and configured by PF. It is very > > > natural request that the PF will view/hide those sysfs files. > > > > Agreed, it's natural if the PF driver adds/removes those files. But I > > don't think it's *essential*, and they *could* be static because of > > this: > > > > > > From the management software point of view, I don't think it matters. > > > > That software already needs to deal with files that don't exist (on > > > > old kernels) and files that contain zero (feature not supported or no > > > > vectors are available). > > > > I wonder if sysfs_update_group() would let us have our cake and eat > > it, too? Maybe we could define these files as static attributes and > > call sysfs_update_group() when the PF driver binds or unbinds? > > > > Makes me wonder if the device core could call sysfs_update_group() > > when binding/unbinding drivers. But there are only a few existing > > callers, and it looks like none of them are for the bind/unbind > > situation, so maybe that would be pointless. > > Also it will be not an easy task to do it in driver/core. Our > attributes need to be visible if driver is bound -> we will call to > sysfs_update_group() after ->bind() callback. It means that in > uwind, we will call to sysfs_update_group() before ->unbind() and > the driver will be still bound. So the check is is_supported() for > driver exists/or not won't be possible. Poking around some more, I found .dev_groups, which might be applicable? The test patch below applies to v5.11 and makes the "bh" file visible in devices bound to the uhci_hcd driver if the function number is odd. This thread has more details and some samples: https://lore.kernel.org/lkml/20190731124349.4474-1-gregkh@xxxxxxxxxxxxxxxxxxx/ On qemu, with 00:1a.[012] and 00:1d.[012] set up as uhci_hcd devices: root@ubuntu:~# ls /sys/bus/pci/drivers/uhci_hcd 0000:00:1a.0 0000:00:1a.2 0000:00:1d.1 bind new_id uevent 0000:00:1a.1 0000:00:1d.0 0000:00:1d.2 module remove_id unbind root@ubuntu:~# grep . /sys/devices/pci0000:00/0000:00:*/bh /dev/null /sys/devices/pci0000:00/0000:00:1a.1/bh:hi bjorn /sys/devices/pci0000:00/0000:00:1d.1/bh:hi bjorn diff --git a/drivers/usb/host/uhci-pci.c b/drivers/usb/host/uhci-pci.c index 9b88745d247f..17ea5bf0dab0 100644 --- a/drivers/usb/host/uhci-pci.c +++ b/drivers/usb/host/uhci-pci.c @@ -297,6 +297,38 @@ static int uhci_pci_probe(struct pci_dev *dev, const struct pci_device_id *id) return usb_hcd_pci_probe(dev, id, &uhci_driver); } +static ssize_t bh_show(struct device *dev, struct device_attribute *attr, + char *buf) +{ + return snprintf(buf, PAGE_SIZE, "hi bjorn\n"); +} +static DEVICE_ATTR_RO(bh); + +static umode_t bh_is_visible(struct kobject *kobj, struct attribute *a, int n) +{ + struct device *dev = kobj_to_dev(kobj); + struct pci_dev *pdev = to_pci_dev(dev); + umode_t mode = (PCI_FUNC(pdev->devfn) % 2) ? 0444 : 0; + + dev_info(dev, "%s mode %o\n", __func__, mode); + return mode; +} + +static struct attribute *bh_attrs[] = { + &dev_attr_bh.attr, + NULL, +}; + +static const struct attribute_group bh_group = { + .attrs = bh_attrs, + .is_visible = bh_is_visible, +}; + +static const struct attribute_group *bh_groups[] = { + &bh_group, + NULL +}; + static struct pci_driver uhci_pci_driver = { .name = hcd_name, .id_table = uhci_pci_ids, @@ -307,7 +339,8 @@ static struct pci_driver uhci_pci_driver = { #ifdef CONFIG_PM .driver = { - .pm = &usb_hcd_pci_pm_ops + .pm = &usb_hcd_pci_pm_ops, + .dev_groups = bh_groups, }, #endif };
