vfs_flagstostr
*ap->a_res = vfs_flagstostr(mp->mnt_flag & MNT_VISFLAGMASK, NULL,
size_t vfs_flagstostr(int flags, const struct mountctl_opt *optp, char *buf, size_t len, int *errorp);
usedbytes += vfs_flagstostr(hmp->hflags, extraopt,