Function shm_alloc

freebsd/kern/uipc_shm.c:853–886

* shmfd object management including creation and reference counting * routines. */

 * routines.
 */
struct shmfd *
shm_alloc(struct ucred *ucred, mode_t mode, bool largepage)
{
	struct shmfd *shmfd;

	shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
	shmfd->shm_size = 0;
	shmfd->shm_uid = ucred->cr_uid;
	shmfd->shm_gid = ucred->cr_gid;
	shmfd->shm_mode = mode;
	if (largepage) {
		shmfd->shm_object = phys_pager_allocate(NULL,
		    &shm_largepage_phys_ops, NULL, shmfd->shm_size,
		    VM_PROT_DEFAULT, 0, ucred);
		shmfd->shm_lp_alloc_policy = SHM_LARGEPAGE_ALLOC_DEFAULT;
	} else {
		shmfd->shm_object = vm_pager_allocate(OBJT_SWAP, NULL,
		    shmfd->shm_size, VM_PROT_DEFAULT, 0, ucred);
	}
	KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
	vfs_timestamp(&shmfd->shm_birthtime);
	shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
	    shmfd->shm_birthtime;
	shmfd->shm_ino = alloc_unr64(&shm_ino_unr);
	refcount_init(&shmfd->shm_refs, 1);
	mtx_init(&shmfd->shm_mtx, "shmrl", NULL, MTX_DEF);
	rangelock_init(&shmfd->shm_rl);
#ifdef MAC
	mac_posixshm_init(shmfd);
	mac_posixshm_create(ucred, shmfd);
#endif

	return (shmfd);
}

struct shmfd *
shm_hold(struct shmfd *shmfd)