Function realloc

freebsd/kern/kern_malloc.c:944–1002

* realloc: change the size of a memory block */

 *	realloc: change the size of a memory block
 */
void *
realloc(void *addr, size_t size, struct malloc_type *mtp, int flags)
{
	uma_zone_t zone;
	uma_slab_t slab;
	unsigned long alloc;
	void *newaddr;

	KASSERT(mtp->ks_version == M_VERSION,
	    ("realloc: bad malloc type version"));
	KASSERT(curthread->td_critnest == 0 || SCHEDULER_STOPPED(),
	    ("realloc: called with spinlock or critical section held"));

	/* realloc(NULL, ...) is equivalent to malloc(...) */
	if (addr == NULL)
		return (malloc(size, mtp, flags));

	/*
	 * XXX: Should report free of old memory and alloc of new memory to
	 * per-CPU stats.
	 */

#ifdef DEBUG_MEMGUARD
	if (is_memguard_addr(addr))
		return (memguard_realloc(addr, size, mtp, flags));
#endif

#ifdef DEBUG_REDZONE
	slab = NULL;
	zone = NULL;
	alloc = redzone_get_size(addr);
#else
	vtozoneslab((vm_offset_t)addr & (~UMA_SLAB_MASK), &zone, &slab);

	/* Sanity check */
	KASSERT(slab != NULL,
	    ("realloc: address %p out of range", (void *)addr));

	/* Get the size of the original block */
	if (!malloc_large_slab(slab))
		alloc = zone->uz_size;
	else
		alloc = malloc_large_size(slab);

	/* Reuse the original block if appropriate */
	if (size <= alloc
	    && (size > (alloc >> REALLOC_FRACTION) || alloc == MINALLOCSIZE))
		return (addr);
#endif /* !DEBUG_REDZONE */

	/* Allocate a new, bigger (or smaller) block */
	if ((newaddr = malloc(size, mtp, flags)) == NULL)
		return (NULL);

	/* Copy over original contents */
	bcopy(addr, newaddr, min(size, alloc));
	free(addr, mtp);
	return (newaddr);