On Fri, Feb 19, 2021 at 09:52:12AM +0200, Leon Romanovsky wrote: > On Thu, Feb 18, 2021 at 04:39:50PM -0600, Bjorn Helgaas wrote: > > 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 solution can be applicable for generic drivers where we can afford > to have custom sysfs files for this driver. In our case, we are talking > about hardware device driver. Both RDMA and netdev are against allowing > for such drivers to create their own sysfs. It will be real nightmare to > have different names/layout/output for the same functionality. > > This .dev_groups moves responsibility over sysfs to the drivers and it > is no-go for us. But it _is_ the driver's responsibility for sysfs files, right? If not, what exactly are you trying to do here, as I am very confused. > Another problem with this approach is addition of VFs, not only every > driver will start to manage its own sysfs, but it will need to iterate > over PCI bus or internal lists to find VFs, because we want to create > .set_msix_vec on VFs after PF is bound. What? I don't understand at all. > So instead of one, controlled place, we will find ourselves with many > genius implementations of the same thing in the drivers. Same _what_ thing? > Bjorn, we really do standard enable/disable flow with out overlay thing. Ok, can you step back and try to explain what problem you are trying to solve first, before getting bogged down in odd details? I find it highly unlikely that this is something "unique", but I could be wrong as I do not understand what you are wanting to do here at all. thanks, greg k-h
