Object API

Data Structures
struct	nl_object
struct	nl_object_ops
	Object Operations. More...

Macros
#define	NLHDR_COMMON
	Common Object Header.
#define	AVAILABLE(A, B, ATTR)   (((A)->ce_mask & (B)->ce_mask) & (ATTR))
	Return true if attribute is available in both objects.
#define	AVAILABLE_MISMATCH(A, B, ATTR)   (((A)->ce_mask ^ (B)->ce_mask) & (ATTR))
	Return true if attribute is available in only one of both objects.
#define	ATTR_MISMATCH(A, B, ATTR, EXPR)
	Return true if attributes mismatch.
#define	ATTR_DIFF(LIST, ATTR, A, B, EXPR)
	Return attribute bit if attribute does not match.

---

Detailed Description

1) Object Definition

   // Define your object starting with the common object header
   struct my_obj {
        NLHDR_COMMON
        int             my_data;
   };
  
   // Fill out the object operations structure
   struct nl_object_ops my_ops = {
        .oo_name        = "my_obj",
        .oo_size        = sizeof(struct my_obj),
   };
  
   // At this point the object can be allocated, you may want to provide a
   // separate _alloc() function to ease allocting objects of this kind.
   struct nl_object *obj = nl_object_alloc(&my_ops);
  
   // And release it again...
   nl_object_put(obj);

2) Allocating additional data

   // You may require to allocate additional data and store it inside
   // object, f.e. assuming there is a field `ptr'.
   struct my_obj {
        NLHDR_COMMON
        void *          ptr;
   };
  
   // And at some point you may assign allocated data to this field:
   my_obj->ptr = calloc(1, ...);
  
   // In order to not introduce any memory leaks you have to release
   // this data again when the last reference is given back.
   static void my_obj_free_data(struct nl_object *obj)
   {
        struct my_obj *my_obj = nl_object_priv(obj);
  
        free(my_obj->ptr);
   }
  
   // Also when the object is cloned, you must ensure for your pointer
   // stay valid even if one of the clones is freed by either making
   // a clone as well or increase the reference count.
   static int my_obj_clone(struct nl_object *src, struct nl_object *dst)
   {
        struct my_obj *my_src = nl_object_priv(src);
        struct my_obj *my_dst = nl_object_priv(dst);
  
        if (src->ptr) {
                dst->ptr = calloc(1, ...);
                memcpy(dst->ptr, src->ptr, ...);
        }
   }
  
   struct nl_object_ops my_ops = {
        ...
        .oo_free_data   = my_obj_free_data,
        .oo_clone       = my_obj_clone,
   };

3) Object Dumping

   static int my_obj_dump_detailed(struct nl_object *obj,
                                   struct nl_dump_params *params)
   {
        struct my_obj *my_obj = nl_object_priv(obj);
  
        // It is absolutely essential to use nl_dump() when printing
        // any text to make sure the dumping parameters are respected.
        nl_dump(params, "Obj Integer: %d\n", my_obj->my_int);
  
        // Before we can dump the next line, make sure to prefix
        // this line correctly.
        nl_new_line(params);
  
        // You may also split a line into multiple nl_dump() calls.
        nl_dump(params, "String: %s ", my_obj->my_string);
        nl_dump(params, "String-2: %s\n", my_obj->another_string);
   }
  
   struct nl_object_ops my_ops = {
        ...
        .oo_dump[NL_DUMP_FULL]  = my_obj_dump_detailed,
   };

4) Object Attributes

   // The concept of object attributes is optional but can ease the typical
   // case of objects that have optional attributes, e.g. a route may have a
   // nexthop assigned but it is not required to.
  
   // The first step to define your object specific bitmask listing all
   // attributes
   #define MY_ATTR_FOO          (1<<0)
   #define MY_ATTR_BAR          (1<<1)
  
   // When assigning an optional attribute to the object, make sure
   // to mark its availability.
   my_obj->foo = 123123;
   my_obj->ce_mask |= MY_ATTR_FOO;
  
   // At any time you may use this mask to check for the availability
   // of the attribute, e.g. while dumping
   if (my_obj->ce_mask & MY_ATTR_FOO)
        nl_dump(params, "foo %d ", my_obj->foo);
  
   // One of the big advantages of this concept is that it allows for
   // standardized comparisons which make it trivial for caches to
   // identify unique objects by use of unified comparison functions.
   // In order for it to work, your object implementation must provide
   // a comparison function and define a list of attributes which
   // combined together make an object unique.
  
   static int my_obj_compare(struct nl_object *_a, struct nl_object *_b,
                             uint32_t attrs, int flags)
   {
        struct my_obj *a = nl_object_priv(_a):
        struct my_obj *b = nl_object_priv(_b):
        int diff = 0;
  
        // We help ourselves in defining our own DIFF macro which will
        // call ATTR_DIFF() on both objects which will make sure to only
        // compare the attributes if required.
        #define MY_DIFF(ATTR, EXPR) ATTR_DIFF(attrs, MY_ATTR_##ATTR, a, b, EXPR)
  
        // Call our own diff macro for each attribute to build a bitmask
        // representing the attributes which mismatch.
        diff |= MY_DIFF(FOO, a->foo != b->foo)
        diff |= MY_DIFF(BAR, strcmp(a->bar, b->bar))
  
        return diff;
   }
  
   // In order to identify identical objects with differing attributes
   // you must specify the attributes required to uniquely identify
   // your object. Make sure to not include too many attributes, this
   // list is used when caches look for an old version of an object.
   struct nl_object_ops my_ops = {
        ...
        .oo_id_attrs            = MY_ATTR_FOO,
        .oo_compare             = my_obj_compare,
   };

---

Macro Definition Documentation

#define NLHDR_COMMON

Value:

int                     ce_refcnt;      \
        struct nl_object_ops *  ce_ops;         \
        struct nl_cache *       ce_cache;       \
        struct nl_list_head     ce_list;        \
        int                     ce_msgtype;     \
        int                     ce_flags;       \
        uint32_t                ce_mask;

Common Object Header.

This macro must be included as first member in every object definition to allow objects to be cached.

Definition at line 184 of file object-api.h.

#define AVAILABLE	(		A,
			B,
			ATTR
	)		(((A)->ce_mask & (B)->ce_mask) & (ATTR))

Return true if attribute is available in both objects.

Parameters:

A	an object
B	another object
ATTR	attribute bit

Returns:

True if the attribute is available, otherwise false is returned.

Definition at line 207 of file object-api.h.

#define AVAILABLE_MISMATCH	(		A,
			B,
			ATTR
	)		(((A)->ce_mask ^ (B)->ce_mask) & (ATTR))

Return true if attribute is available in only one of both objects.

Parameters:

A	an object
B	another object
ATTR	attribute bit

Returns:

True if the attribute is available in only one of both objects, otherwise false is returned.

Definition at line 218 of file object-api.h.

#define ATTR_MISMATCH	(		A,
			B,
			ATTR,
			EXPR
	)

Value:

(AVAILABLE_MISMATCH(A, B, ATTR) || \
                                         (AVAILABLE(A, B, ATTR) && (EXPR)))

Return true if attributes mismatch.

Parameters:

A	an object
B	another object
ATTR	attribute bit
EXPR	Comparison expression

This function will check if the attribute in question is available in both objects, if not this will count as a mismatch.

If available the function will execute the expression which must return true if the attributes mismatch.

Returns:

True if the attribute mismatch, or false if they match.

Definition at line 235 of file object-api.h.

#define ATTR_DIFF	(		LIST,
			ATTR,
			A,
			B,
			EXPR
	)

Value:

({      int diff = 0; \
        if (((LIST) & (ATTR)) && ATTR_MISMATCH(A, B, ATTR, EXPR)) \
                diff = ATTR; \
        diff; })

Return attribute bit if attribute does not match.

Parameters:

LIST	list of attributes to be compared
ATTR	attribute bit
A	an object
B	another object
EXPR	Comparison expression

This function will check if the attribute in question is available in both objects, if not this will count as a mismatch.

If available the function will execute the expression which must return true if the attributes mismatch.

In case the attributes mismatch, the attribute is returned, otherwise 0 is returned.

   diff |= ATTR_DIFF(attrs, MY_ATTR_FOO, a, b, a->foo != b->foo);

Definition at line 259 of file object-api.h.