Question abt piece of code in pci_Driver.c

["rajesh ms" <torajeshms@xxxxxxxxxxxxxx>]

 
Hi all,

            I have got a question.

I was going through pci_Driver.c. Then i found


drv = to_pci_driver(dev->driver);

and
drv is of type struct pci_driver*

#define     to_pci_driver(drv) container_of(drv,struct pci_driver, driver)

#define container_of(ptr, type, member)
({               \
        const typeof( ((type *)0)->member ) *__mptr = (ptr);     \
        (type *)( (char *)__mptr - offsetof(type,member) );})



Then i substituted for all parameters and got this

drv = ({

        const struct device_driver *__mptr = (dev->driver);
        (struct pci_driver*)( (char *)__mptr - offsetof(struct pci_driver,driver) );
     
     });

1)What value will be stored in drv? Is there any rule to find this,  ( Like last statement ----- My Guess )

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.


Thanks in advance

Rajesh