On Fri, Feb 11, 2005 at 09:35:48AM -0000, rajesh ms wrote: > Hi, > > > > 2)We are declaring const struct device_driver pointer and substracting > > > the offset value (struct device_driver * is a member of struct > > > pci_driver )and getting the address of struct pci_driver which may > > > contain some data that is irrelevent to struct pci_driver. If this is > > > the return value whether this will cause problems? How this is dealt > > > in the code. > > > >Look at the definition of struct pci_driver. It contains a struct > >device_driver. When passed a pointer to a struct device_driver, the > >code "knows" that it is safe to treat it as a part of the struct > >pci_driver. So it moves backwards in memory to get the real pointer to > >the struct pci_driver and everyone is happy. > > > >This convention is used a _lot_ in the driver model code in the kernel > >to allow for "inheritance" in C. > > Thanks Greg, > But i am worried about the values that will be there in the pci_driver > struct before member struct device_driver. If they are used , I think > it will cause troubles. Am i right? If so how it is handled? I do not understand the question. Please study how the pci_driver struct is created, I think it will show that there isn't a problem here (that, and the fact that the code is working :) thanks, greg k-h -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
