vnd_comp_header
struct vnd_comp_header *ch;
ch = malloc(sizeof(struct vnd_comp_header),
sizeof(struct vnd_comp_header), 0, UIO_SYSSPACE,
if ((vattr.va_size < sizeof(struct vnd_comp_header)) ||
(vattr.va_size - sizeof(struct vnd_comp_header) <
sizeof(struct vnd_comp_header), UIO_SYSSPACE,