On Fri, Sep 26, 2014 at 5:37 PM, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > > On Tue, Sep 23, 2014 at 04:46:06PM +0200, Antonios Motakis wrote: > > As already demonstrated with PCI [1] and the platform bus [2], a > > driver_override property in sysfs can be used to bypass the id matching > > of a device to a AMBA driver. This can be used by VFIO to bind to any AMBA > > device requested by the user. > > > > [1] http://lists-archives.com/linux-kernel/28030441-pci-introduce-new-device-binding-path-using-pci_dev-driver_override.html > > [2] https://www.redhat.com/archives/libvir-list/2014-April/msg00382.html > > > > Signed-off-by: Antonios Motakis <a.motakis@xxxxxxxxxxxxxxxxxxxxxx> > > I have to ask why this is even needed in the first place. To take the > example in [2], what's wrong with: > > echo fff51000.ethernet > /sys/bus/platform/devices/fff51000.ethernet/driver/unbind > echo fff51000.ethernet > /sys/bus/platform/drivers/vfio-platform/bind > > and similar for AMBA. > > All we would need to do is to introduce a way of having a driver accept > explicit bind requests. > > In any case: > > > +static ssize_t driver_override_store(struct device *_dev, > > + struct device_attribute *attr, > > + const char *buf, size_t count) > > +{ > > + struct amba_device *dev = to_amba_device(_dev); > > + char *driver_override, *old = dev->driver_override, *cp; > > + > > + if (count > PATH_MAX) > > + return -EINVAL; > > + > > + driver_override = kstrndup(buf, count, GFP_KERNEL); > > + if (!driver_override) > > + return -ENOMEM; > > + > > + cp = strchr(driver_override, '\n'); > > + if (cp) > > + *cp = '\0'; > > I hope that is not replicated everywhere. This allows up to a page to be > allocated, even when the first byte may be a newline. This is wasteful. > > How about: > > if (count > PATH_MAX) > return -EINVAL; > > cp = strnchr(buf, count, '\n'); > if (cp) > count = cp - buf - 1; > > if (count) { > driver_override = kstrndup(buf, count, GFP_KERNEL); > if (!driver_override) > return -ENOMEM; > } else { > driver_override = NULL; > } > > kfree(dev->driver_override); > dev->driver_override = driver_override; I implemented something along this lines and tested it a bit. The kernel already splits the input by newlines, and the function is being called for each one separately; so this change doesn't save any memory. > > Also: > > > +static ssize_t driver_override_show(struct device *_dev, > > + struct device_attribute *attr, char *buf) > > +{ > > + struct amba_device *dev = to_amba_device(_dev); > > + > > + return sprintf(buf, "%s\n", dev->driver_override); > > +} > > Do we really want to do a NULL pointer dereference here? > > -- > FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up > according to speedtest.net. -- Antonios Motakis Virtual Open Systems -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
