[+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. > > From my point of view, pci_enable_vf_overlay() or > > pci_disable_vfs_overlay() are also clutter, at least compared to > > static sysfs attributes. > > > > > > I see a hint that Alex might have requested this "only visible when PF > > > > driver supports it" functionality, but I don't see that email on > > > > linux-pci, so I missed the background. > > > > > > First version of this patch had static files solution. > > > https://lore.kernel.org/linux-pci/20210103082440.34994-2-leon@xxxxxxxxxx/#Z30drivers:pci:iov.c > > > > Thanks for the pointer to the patch. Can you point me to the > > discussion about why we should use the "only visible when PF driver > > supports it" model? > > It is hard to pinpoint specific sentence, this discussion is spread > across many emails and I implemented it in v4. > > See this request from Alex: > https://lore.kernel.org/linux-pci/20210114170543.143cce49@xxxxxxxxxxxxxxxxxxxxx/ > and this is my acknowledge: > https://lore.kernel.org/linux-pci/20210116082331.GL944463@unreal/ > > BTW, I asked more than once how these sysfs knobs should be handled > in the PCI/core. Thanks for the pointers. This is the first instance I can think of where we want to create PCI core sysfs files based on a driver binding, so there really isn't a precedent. > > [1] https://lore.kernel.org/linux-pci/YBmG7qgIDYIveDfX@xxxxxxxxx/ > > [2] https://lore.kernel.org/linux-pci/20200716110423.xtfyb3n6tn5ixedh@pali/
