From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:32658 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726579AbhANNVA (ORCPT ); Thu, 14 Jan 2021 08:21:00 -0500 Subject: Re: [RFC 1/1] s390/pci: expose UID checking state in sysfs References: <20210113185500.GA1918216@bjorn-Precision-5520> From: Niklas Schnelle Message-ID: <675aa466-59ea-cf8a-6eec-caa6478ba4cd@linux.ibm.com> Date: Thu, 14 Jan 2021 14:20:10 +0100 MIME-Version: 1.0 In-Reply-To: <20210113185500.GA1918216@bjorn-Precision-5520> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit List-ID: To: Bjorn Helgaas , Christian Brauner Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Pierre Morel , Peter Oberparleiter , Viktor Mihajlovski On 1/13/21 7:55 PM, Bjorn Helgaas wrote: > On Wed, Jan 13, 2021 at 08:47:58AM +0100, Niklas Schnelle wrote: >> On 1/12/21 10:50 PM, Bjorn Helgaas wrote: >>> On Mon, Jan 11, 2021 at 10:38:57AM +0100, Niklas Schnelle wrote: >>>> We use the UID of a zPCI adapter, or the UID of the function zero if >>>> there are multiple functions in an adapter, as PCI domain if and only if >>>> UID Checking is turned on. >>>> Otherwise we automatically generate domains as devices appear. >>>> >>>> The state of UID Checking is thus essential to know if the PCI domain >>>> will be stable, yet currently there is no way to access this information >>>> from userspace. >>>> So let's solve this by showing the state of UID checking as a sysfs >>>> attribute in /sys/bus/pci/uid_checking > >>>> +/* Global zPCI attributes */ >>>> +static ssize_t uid_checking_show(struct kobject *kobj, >>>> + struct kobj_attribute *attr, char *buf) >>>> +{ >>>> + return sprintf(buf, "%i\n", zpci_unique_uid); >>>> +} >>>> + >>>> +static struct kobj_attribute sys_zpci_uid_checking_attr = >>>> + __ATTR(uid_checking, 0444, uid_checking_show, NULL); >>> >>> Use DEVICE_ATTR_RO instead of __ATTR. >> >> It's my understanding that DEVICE_ATTR_* is only for >> per device attributes. This one is global for the entire >> Z PCI. I just tried with BUS_ATTR_RO instead >> and that works but only if I put the attribute at >> /sys/bus/pci/uid_checking instead of with a zpci >> subfolder. This path would work for us too, we >> currently don't have any other global attributes >> that we are planning to expose but those could of >> course come up in the future. > > Ah, I missed the fact that this is a kobj_attribute, not a > device_attribute. Maybe KERNEL_ATTR_RO()? Very few uses so far, but > seems like it might fit? > > Bjorn > KERNEL_ATTR_* is currently not exported in any header. After adding it to include/linuc/sysfs.h it indeed works perfectly. Adding Christian Brauner as suggested by get_maintainers for their opinion. I'm of course willing to provide a patch for that move should it be desired. @Bjorn apart from the correct macro do you have a preference for either suggested path /sys/bus/pci/zpci/uid_checking vs /sys/bus/pci/uid_checking? For completeness some further internal discussion lets us tend to rather name it to "unique_uids" but I guess that doesn't make a difference to non s390 people ;-)