How to create a generic function to take hashtable name and a struct as parameters in a kernel module? - hashtable

Question

I'm currently writing a kernel module which uses multiple hashtables to store different structures. How would I go about implementing a single generic function which would take the hashtable name, hash key and structure to be stored as parameters and do the corresponding store operation?
Here is my hashtable and structure definition.
static DEFINE_HASHTABLE(count, 7);
struct mystruct {
int data ;
struct hlist_node my_hash_list ;
};
Here is my store code ( I seem to be getting a null pointer error if I increment temp->data directly instead of doing it my roundabout add and del way :( )
struct mystruct *temp;
struct mystruct *first;
temp = kmalloc(sizeof(struct mystruct),GFP_KERNEL);
first = kmalloc(sizeof(struct mystruct),GFP_KERNEL);
hash = command;
hash_for_each_possible(count, temp, my_hash_list,hash){
first->data=temp->data+1;
printk("Count: %d\n",first->data);
hash_add(count, &(first->my_hash_list), hash);
hash_del(&(temp->my_hash_list));
return;
}
first->data=1;
hash_add(count, &(first->my_hash_list), hash);
This is for the count hashtable and mystruct structure. Is it possible to create a kernel module function to have a placeholder pointer to any structure and kmalloc memory to that struct? Also how to pass the hashtable name as a parameter?

Answer 1

You cannot create a function which accepts name of the hashtable: it is prohibited by C language. So, your function may only accept a pointer to the hashtable. But because it accepts a pointer, you may no longer use macros like hash_add, which requires name.
You have 2 possibilites:
Creating function-like macro, so it can accept hashtable name, structure and other definitions.
This way is commonly used by Linux kernel, which tends to be fast. Note, that operations like hash_add, hash_for_each_possible are macros too.
Wrap hashtable into your own structure. Into the same structure you need to add all additional information about hash elements: size (for kmalloc), getter of the key from the element (for search) and setter for it(for inserter), and so on.
Something like
struct my_hashtable {
DECLARE_HASHTABLE(count, 7);
size_t obj_size;
unsigned long (*get_key)(void* obj);
void (*set_key)(void* obj, unsigned long key);
};