Hello, Shyam! Last year (actually 2 days ago) when you posted your question I was thinking about 'container_of' macro, but I was not sure because the question looked like a schedulers-related question. But it's just a question about 'container_of'. On 13:52 Fri 02 Jan , Shyam Burkule wrote: > > Actually my question is that if we have pointer to list_head(embedded in > task_struct), then how kernel gets address of corresponding task_struct. > Here I just given example of scheduler, where the kernel need this > operation. > > I traverse kernel code and for such operation kernel always comes to > *container_of* micro, now I am trying to understand how this function works? Please, distinguish functions and macros, container_of is a macro. Usage of 'container_of' with lists: If we want to add objects of a structure (say, 'struct abc') to a list, we can just add a 'struct list_head list' as a member of 'struct abc', then we will be able to link the structures 'struct list_head' into a list. How we can walk around the list of 'struct list_head's (we know the next and the previous node for each node in the list). But remember that those 'struct list_head's are inside our 'struct abc'. If an instance of 'struct abc' (say, 'struct abc myabc') has memory address X, then the address in memory of its member 'list' equals (X + [offset of 'list' in our 'struct abc']). The "offset of 'list' in our 'struct abc'" is contant for any instance of the structure 'abc', so we can calculate it at compile time. And 'container_of' is useful when we want to get the pointer (pointer ~= address) to myabc (&myabc) while we only have a pointer to myabc.list (&myabc.list): struct list_head *p_list; struct abc *p_myabc; p_list = (...something...); p_myabc = container_of (p_list, struct abc, list); This topic (container_of) has already been discussed here, you can find it using Google "container_of" -> "I'm feeling lucky" button... ;) The GregKH's "answer" (I'd like to say "article") is here: http://www.kroah.com/log/linux/container_of.html Alexander -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
