FRR includes wrappers arround malloc() and free() that count the number of objects currently allocated, for each of a defined MTYPE.

To this extent, there are memory groups and memory types. Each memory type must belong to a memory group, this is used just to provide some basic structure.


DEFINE_MGROUP(      MYDAEMON, "My daemon's memory")
DEFINE_MTYPE(       MYDAEMON, MYNEIGHBOR,     "Neighbor entry")

struct neigh *neighbor_new(const char *name)
        struct neigh *n = XMALLOC(MYNEIGHBOR, sizeof(*n));
        n->name = XSTRDUP(MYNEIGHBORNAME, name);
        return n;

void neighbor_free(struct neigh *n)
        XFREE(MYNEIGHBORNAME, n->name);



This macro forward-declares a memory group and should be placed in a .h file. It expands to an extern struct memgroup statement.

DEFINE_MGROUP(mname, description)

Defines/implements a memory group. Must be placed into exactly one .c file (multiple inclusion will result in a link-time symbol conflict).

Contains additional logic (constructor and destructor) to register the memory group in a global list.


Forward-declares a memory type and makes MTYPE_name available for use. Note that the MTYPE_ prefix must not be included in the name, it is automatically prefixed.

MTYPE_name is created as a static const symbol, i.e. a compile-time constant. It refers to an extern struct memtype _mt_name, where name is replaced with the actual name.

DEFINE_MTYPE(group, name, description)

Define/implement a memory type, must be placed into exactly one .c file (multiple inclusion will result in a link-time symbol conflict).

Like DEFINE_MGROUP, this contains actual code to register the MTYPE under its group.

DEFINE_MTYPE_STATIC(group, name, description)

Same as DEFINE_MTYPE, but the DEFINE_MTYPE_STATIC variant places the C static keyword on the definition, restricting the MTYPE’s availability to the current source file. This should be appropriate in >80% of cases.


Daemons currently have daemon_memory.[ch] files listing all of their MTYPEs. This is not how it should be, most of these types should be moved into the appropriate files where they are used. Only a few MTYPEs should remain non-static after that.


void *XMALLOC(struct memtype *mtype, size_t size)
void *XCALLOC(struct memtype *mtype, size_t size)
void *XSTRDUP(struct memtype *mtype, size_t size)

Allocation wrappers for malloc/calloc/realloc/strdup, taking an extra mtype parameter.

void *XREALLOC(struct memtype *mtype, void *ptr, size_t size)

Wrapper around realloc() with MTYPE tracking. Note that ptr may be NULL, in which case the function does the same as XMALLOC (regardless of whether the system realloc() supports this.)

void XFREE(struct memtype *mtype, void *ptr)

Wrapper around free(), again taking an extra mtype parameter. This is actually a macro, with the following additional properties:

  • the macro contains ptr = NULL
  • if ptr is NULL, no operation is performed (as is guaranteed by system implementations.) Do not surround XFREE with if (ptr != NULL) checks.