On Wed, May 06, 2020 at 05:32:26PM +0530, Sreyan Chakravarty wrote: > I am reading Robert Love's Book Linux Kernel Development( > https://rads.stackoverflow.com/amzn/click/com/B003V4ATI0). > > It uses the 2.6.33 kernel for demonstration. > > I have been going through certain parts of the source and can't find out > where is the initial definition of many things. A lot of things are just > used, like "magic" without me finding the definition. > > One example: > > static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq) > { > struct rb_node *left = cfs_rq->rb_leftmost; > > if (!left) > return NULL; > > return rb_entry(left, struct sched_entity, run_node); > } include/linux/rbtree.h:#define rb_entry(ptr, type, member) container_of(ptr, type, member) So rb_entry is a macro and it basically rewrites the return line into another macro: return container_of(left, struct sched_entity, run_node); And that one gives the address of the struct sched_entity that left is a member of by subtracting the offset from the struct start to run_node member: struct sched_entity { - ... | ... | offset ... | ... - struct rb_node run_node; <=== left points here ... } https://stackoverflow.com/questions/15832301/understanding-container-of-macro-in-the-linux-kernel -- Valentin _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
