Function ktr_writerequest

freebsd/kern/kern_ktrace.c:1183–1305

}

static void
ktr_writerequest(struct thread *td, struct ktr_request *req)
{
	struct ktr_header *kth;
	struct vnode *vp;
	struct proc *p;
	struct ucred *cred;
	struct uio auio;
	struct iovec aiov[3];
	struct mount *mp;
	int datalen, buflen, vrele_count;
	int error;

	/*
	 * We hold the vnode and credential for use in I/O in case ktrace is
	 * disabled on the process as we write out the request.
	 *
	 * XXXRW: This is not ideal: we could end up performing a write after
	 * the vnode has been closed.
	 */
	mtx_lock(&ktrace_mtx);
	vp = td->td_proc->p_tracevp;
	cred = td->td_proc->p_tracecred;

	/*
	 * If vp is NULL, the vp has been cleared out from under this
	 * request, so just drop it.  Make sure the credential and vnode are
	 * in sync: we should have both or neither.
	 */
	if (vp == NULL) {
		KASSERT(cred == NULL, ("ktr_writerequest: cred != NULL"));
		mtx_unlock(&ktrace_mtx);
		return;
	}
	VREF(vp);
	KASSERT(cred != NULL, ("ktr_writerequest: cred == NULL"));
	crhold(cred);
	mtx_unlock(&ktrace_mtx);

	kth = &req->ktr_header;
	KASSERT(((u_short)kth->ktr_type & ~KTR_DROP) < nitems(data_lengths),
	    ("data_lengths array overflow"));
	datalen = data_lengths[(u_short)kth->ktr_type & ~KTR_DROP];
	buflen = kth->ktr_len;
	auio.uio_iov = &aiov[0];
	auio.uio_offset = 0;
	auio.uio_segflg = UIO_SYSSPACE;
	auio.uio_rw = UIO_WRITE;
	aiov[0].iov_base = (caddr_t)kth;
	aiov[0].iov_len = sizeof(struct ktr_header);
	auio.uio_resid = sizeof(struct ktr_header);
	auio.uio_iovcnt = 1;
	auio.uio_td = td;
	if (datalen != 0) {
		aiov[1].iov_base = (caddr_t)&req->ktr_data;
		aiov[1].iov_len = datalen;
		auio.uio_resid += datalen;
		auio.uio_iovcnt++;