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Wysocki" Subject: Re: [PATCH v10 4/8] PCI/sysfs: Allow userspace to query and set device reset mechanism Message-ID: <20210728185831.isdqa5t5oxxjfhnv@archlinux> References: <20210728175950.q75qcrfas5mcjych@archlinux> <20210728181333.GA836307@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210728181333.GA836307@bjorn-Precision-5520> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 21/07/28 01:13PM, Bjorn Helgaas wrote: > On Wed, Jul 28, 2021 at 11:29:50PM +0530, Amey Narkhede wrote: > > On 21/07/27 06:28PM, Bjorn Helgaas wrote: > > > On Fri, Jul 09, 2021 at 06:08:09PM +0530, Amey Narkhede wrote: > > > > Add reset_method sysfs attribute to enable user to query and set user > > > > preferred device reset methods and their ordering. > > > > > > > > Co-developed-by: Alex Williamson > > > > Signed-off-by: Alex Williamson > > > > Signed-off-by: Amey Narkhede > > > > --- > > > > Documentation/ABI/testing/sysfs-bus-pci | 19 +++++ > > > > drivers/pci/pci-sysfs.c | 103 ++++++++++++++++++++++++ > > > > 2 files changed, 122 insertions(+) > > > > > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci > > > > index ef00fada2..43f4e33c7 100644 > > > > --- a/Documentation/ABI/testing/sysfs-bus-pci > > > > +++ b/Documentation/ABI/testing/sysfs-bus-pci > > > > @@ -121,6 +121,25 @@ Description: > > > > child buses, and re-discover devices removed earlier > > > > from this part of the device tree. > > > > > > > > +What: /sys/bus/pci/devices/.../reset_method > > > > +Date: March 2021 > > > > +Contact: Amey Narkhede > > > > +Description: > > > > + Some devices allow an individual function to be reset > > > > + without affecting other functions in the same slot. > > > > + > > > > + For devices that have this support, a file named > > > > + reset_method will be present in sysfs. Initially reading > > > > + this file will give names of the device supported reset > > > > + methods and their ordering. After write, this file will > > > > + give names and ordering of currently enabled reset methods. > > > > + Writing the name or comma separated list of names of any of > > > > + the device supported reset methods to this file will set > > > > + the reset methods and their ordering to be used when > > > > + resetting the device. Writing empty string to this file > > > > + will disable ability to reset the device and writing > > > > + "default" will return to the original value. > > > > + > > > > What: /sys/bus/pci/devices/.../reset > > > > Date: July 2009 > > > > Contact: Michael S. Tsirkin > > > > > [...] > > > > > > + int i; > > > > + > > > > + if (sysfs_streq(name, "")) > > > > + continue; > > > > + > > > > + name = strim(name); > > > > + > > > > + for (i = 1; i < PCI_NUM_RESET_METHODS; i++) { > > > > + if (sysfs_streq(name, pci_reset_fn_methods[i].name) && > > > > + !pci_reset_fn_methods[i].reset_fn(pdev, 1)) { > > > > + reset_methods[n++] = i; > > > > > > Can we build this directly in pdev->reset_methods[] so we don't need > > > the memcpy() below? > > > > > This is to avoid writing partial values directly to dev->reset_methods. > > So for example if user writes flr,unsupported_value then > > dev->reset_methods should not be modified even though flr is valid reset > > method in this example to avoid partial writes. Either operation(in this > > case writing supported reset methods to reset_method attr) succeeds > > completely or it fails othewise. > > I guess the question is, if somebody writes > > flr junk bus > > and we set the supported methods to "flr bus", is that OK? It seems > OK to me; obviously we have to protect ourselves from attack, but > over-zealous checking can make things unnecessarily complicated. The problem is once we encounter "junk" we return -EINVAL so in your example we only set flr. Thanks, Amey