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<0a3936872d93511ac76cba04edc47f598950d7ee.camel@linux.ibm.com> Subject: Re: [PATCH] PCI: s390: Expose the UID as an arch specific PCI slot attribute From: Niklas Schnelle To: Benjamin Block Cc: Bjorn Helgaas , Lukas Wunner , Gerald Schaefer , Christian Borntraeger , Gerd Bayer , Matthew Rosato , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle , Julian Ruess , Peter Oberparleiter , Ramesh Errabolu , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Date: Wed, 08 Oct 2025 13:05:13 +0200 In-Reply-To: <20250930090949.GA15786@p1gen4-pw042f0m.boeblingen.de.ibm.com> References: <20250924-uid_slot-v1-1-09ae04f48c57@linux.ibm.com> <20250926142714.GB17059@p1gen4-pw042f0m.boeblingen.de.ibm.com> <20250930090949.GA15786@p1gen4-pw042f0m.boeblingen.de.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; prefer-encrypt=mutual; keydata=mQINBGHm3M8BEAC+MIQkfoPIAKdjjk84OSQ8erd2OICj98+GdhMQpIjHXn/RJdCZLa58k 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On Tue, 2025-09-30 at 11:09 +0200, Benjamin Block wrote: > On Fri, Sep 26, 2025 at 08:25:07PM +0200, Niklas Schnelle wrote: > > On Fri, 2025-09-26 at 16:27 +0200, Benjamin Block wrote: > > > > +extern const struct attribute_group zpci_slot_attr_group; > > > > + > > > > +#define ARCH_PCI_SLOT_GROUPS (&zpci_slot_attr_group) > > >=20 > > > I don't know the history exactly, but this can't be easily extended l= ike the > > > other group above `ARCH_PCI_DEV_GROUPS`. > > >=20 > > > =C2=A0=C2=A0=C2=A0=C2=A0(&zpci_slot_attr_group, \ > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0&zpci_slot_attr_group_b) > > >=20 > > > Won't compile. The way `ARCH_PCI_DEV_GROUPS` does it, attaching a dif= ferent > > > group is just adding a new line. > >=20 > > Without the parenthesis it should. I only added them because otherwise > > checkpatch complains and it's still valid for a single item to have > > parenthesis. >=20 > It's not like checkpatch is the last arbiter of truth here, especially si= nd we > already have a case without parenthesis; but I guess if we ever need to e= xtend > the list, we can remove the parenthesis again. Yes that was my thought too. >=20 > > > > diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c > > > > index 0ee0924cfab7e5d22468fb197ee78cac679d8c13..997dff3796094680d9a= 3f0b6eb27a89fa1ed30b2 100644 > > > > --- a/arch/s390/pci/pci_sysfs.c > > > > +++ b/arch/s390/pci/pci_sysfs.c > > > > @@ -178,6 +178,17 @@ static ssize_t index_show(struct device *dev, > > > > =C2=A0} > > > > =C2=A0static DEVICE_ATTR_RO(index); > > > > =C2=A0 > > > > --- snip --- > > > > +{ > > > > + struct zpci_dev *zdev =3D container_of(slot->hotplug, struct zpci= _dev, > > > > + hotplug_slot); > > > > + > > > > + return sysfs_emit(buf, "0x%x\n", zdev->uid); > > >=20 > > > Do we need a special case for when `uid` is 0? That would imply the u= id is > > > invalid, right? Would we want to return an error in that case (-EINVA= L, or > > > smth)?=20 > > >=20 > > > Also, do we want to use the same format as in `zpci_setup_bus_resourc= es()` > > > with the 4 leading 0's (`0x%04x`)? > >=20 > > I chose to match the "uid" device attribute here ("zpci_attr(uid, > > "0x%x\n", uid)" in the beginning of the same file). >=20 > Ah right, fair enough. >=20 > > This doesn't > > special case UID 0. You are right that this is an invalid UID though. > > It also still exposes the UID even if it is not guaranteed to be > > unique. But we'll make that setting known to user-space separately. > > I feel like knowing the UIDs can still be helpful even when they are > > not unique, for example to check that they've been set correctly from > > within Linux before enabling UID Checking. >=20 > I don't mind the case where the UID is not checked for uniqueness (the na= ming > is confusing in any case, since the U doesn't stand for unique), I was ju= st > wondering whether printing an invalid UID makes sense. I think those are > distinct cases.=20 > It might be easier to 'encode' this knowledge about an UID being "invalid= " > here, rather than 'encoding' it in every single user that might read this > attribute. >=20 > I guess the same can be said for the old `uid` attribute that is attached= to > the PCI device, but that was introduced by Sebastian a long time ago. My thought here is that any program that deals with this new uid attribute would potentially also deal with the existing per-device attribute. I'd not want to change the existing attribute so then I think it is best if applications just have to deal with a single "UID as '0x' prefixed hex with 0 meaning unset" encoding. It's also that this invalid/unset case does happen as the machine configuration does allow UIDs to be unset, so it's not really an error case. Thanks, Niklas