On 8/25/2019 10:43 PM, Eric Wong wrote: > This macro is popular within the Linux kernel for supporting > intrusive data structures such as linked lists, red-black trees, > and chained hash tables while allowing the compiler to do > type checking. > > I intend to use this to remove the limitation of "hashmap_entry" > being location-dependent and to allow more compile-time type > checking. > > This macro already exists in our source as "list_entry" in > list.h and making "list_entry" an alias to "container_of" > as the Linux kernel has done is a possibility. [snip] > +/* > + * container_of - Get the address of an object containing a field. > + * > + * @ptr: pointer to the field. > + * @type: type of the object. > + * @member: name of the field within the object. > + */ > +#define container_of(ptr, type, member) \ > + ((type *) ((char *)(ptr) - offsetof(type, member))) > + > #endif
I think it would be good to include at least one use of this macro in this patch. As it stands, I need to look at the next patch to make sense of what this is doing. It took me a little while to parse what is happening here. 'ptr' is a pointer to the generic struct (in our case, 'struct hashmap_entry *'), while 'type' is the parent type, and 'member' is the name of the member in 'type' that is of type typeof(*ptr). Perhaps this is easier to grok for others than it was for me. -Stolee
