On Fri, 4 Dec 2009, Greg KH wrote: > On Fri, Dec 04, 2009 at 06:50:35PM -0500, Alan Stern wrote: > > On Fri, 4 Dec 2009, Dmitry Torokhov wrote: > > > > > > Maybe reference counting is inelegant; it depends on your point of > > > > view. Can you think of a more elegant way to make sure that a pointer > > > > isn't stale? > > > > > > Yes, just say "no" to device_create() and friends. > > > > device_create() wasn't used in the case Oliver is discussing. > > It was implied, as you had a pointer to the device, not the device > itself. Not necessarily. For example, the serial drivers have pointers to struct tty, not the tty structures themselves. That doesn't imply the tty structures were constructed using device_create(). > > > Embed device structure in > > > yours, > > > > You can't do that when the device structure wasn't created by your > > driver. > > But for USB devices, it is part of the device you are handed. Same goes > for PCI devices, and most other types of drivers, right? Yes. Dmitry's word "yours" is ambiguous here. It's true that struct pci_device contains an embedded struct device. But for example, struct ehci_hcd doesn't -- even when the EHCI controller is a PCI device. So if you are the ehci-hcd driver, which structure is "yours": the struct pci_device or the struct ehci_hcd? > > > be mindful of lifetime rules and only use "your" device (i.e device > > > bound to your driver). > > > > What do you mean by "use"? In Oliver's case he wasn't using the > > device, he was using the device structure. (Maybe that's what you > > meant.) > > I think that is what is meant here. > > > And he wanted to use it at a time when it wasn't bound to his > > driver, because userspace still had an open file reference to it. > > There isn't really any way around this. > > But you still have a valid device, just not maybe a driver bound to it. If a driver isn't bound to it then you don't know whether the device structure is valid or not. It could have been deallocated. Unless you have taken a reference to it -- then you know. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
