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Thu, 14 Jan 2021 15:06:11 +0000 (GMT) Received: from [9.145.25.124] (unknown [9.145.25.124]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 14 Jan 2021 15:06:11 +0000 (GMT) Subject: Re: [RFC 1/1] s390/pci: expose UID checking state in sysfs To: Greg Kroah-Hartman , Christian Brauner Cc: Bjorn Helgaas , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Pierre Morel , Peter Oberparleiter , Viktor Mihajlovski References: <20210113185500.GA1918216@bjorn-Precision-5520> <675aa466-59ea-cf8a-6eec-caa6478ba4cd@linux.ibm.com> <20210114134453.bkfik4zjt5ehz6d5@wittgenstein> From: Niklas Schnelle Message-ID: Date: Thu, 14 Jan 2021 16:06:11 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-14_05:2021-01-14,2021-01-14 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 mlxlogscore=999 spamscore=0 clxscore=1015 adultscore=0 phishscore=0 suspectscore=0 lowpriorityscore=0 malwarescore=0 priorityscore=1501 impostorscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101140085 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 1/14/21 2:58 PM, Greg Kroah-Hartman wrote: > On Thu, Jan 14, 2021 at 02:44:53PM +0100, Christian Brauner wrote: >> On Thu, Jan 14, 2021 at 02:20:10PM +0100, Niklas Schnelle wrote: >>> >>> >>> 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 >> >> Hey Niklas et al. :) >> >> I think this will need input from Greg. He should be best versed in >> sysfs attributes. The problem with KERNEL_ATTR_* to me seems that it's >> supposed to be kernel internal. Now, that might just be a matter of >> renaming the macro but let's see whether Greg has any better idea or >> more questions. :) > > The big question is, why are you needing this? > > No driver or driver subsystem should EVER be messing with a "raw" > kobject like this. Just use the existing DEVICE_* macros instead > please. > > If you are using a raw kobject, please ask me how to do this properly, > as that is something that should NEVER show up in the /sys/devices/* > tree. Otherwise userspace tools will break. > > thanks, > > greg k-h Hi Greg, this is for an architecture specific but global i.e. not device bound PCI attribute. That's why DEVICE_ATTR_* does not work. BUS_ATTR_* would work but only if we place the attribute directly under /sys/bus/pci/new_attr. I'm aware that this is quite unusual in fact I couldn't find anything similar. That's why this is an RFC, with a lengthy cover letter explaining our use case, that I sent to Bjorn to figure out where to even place the attribute. So I guess this is indeed me asking you how to do this properly. That said it does not show up under /sys/devices/* only /sys/bus/pci/*. Best regards, Niklas