diff --git a/sys/kern/subr_uio.c b/sys/kern/subr_uio.c
--- a/sys/kern/subr_uio.c
+++ b/sys/kern/subr_uio.c
@@ -287,6 +287,37 @@
 	return (error);
 }
 
+/*
+ * Advance the pointer in the uio by offset.
+ */
+void
+uioadvance(struct uio *uio, size_t offset)
+{
+
+	MPASS(uio->uio_resid >= offset);
+
+	while (offset > 0) {
+		struct iovec *iov;
+		size_t cnt;
+
+		KASSERT(uio->uio_iovcnt > 0,
+		    ("%s: uio %p iovcnt underflow", __func__, uio));
+		iov = uio->uio_iov;
+		if ((cnt = iov->iov_len) == 0) {
+			uio->uio_iov++;
+			uio->uio_iovcnt--;
+			continue;
+		}
+		if (cnt > offset)
+			cnt = offset;
+		iov->iov_base = (char *)iov->iov_base + cnt;
+		iov->iov_len -= cnt;
+		uio->uio_resid -= cnt;
+		uio->uio_offset += cnt;
+		offset -= cnt;
+	}
+}
+
 /*
  * Wrapper for uiomove() that validates the arguments against a known-good
  * kernel buffer.  Currently, uiomove accepts a signed (n) argument, which
diff --git a/sys/sys/uio.h b/sys/sys/uio.h
--- a/sys/sys/uio.h
+++ b/sys/sys/uio.h
@@ -90,6 +90,7 @@
 	    vm_paddr_t dst, size_t len);
 int	physcopyout_vlist(vm_paddr_t src, struct bus_dma_segment *dst,
 	    off_t offset, size_t len);
+void	uioadvance(struct uio *, size_t);
 int	uiomove(void *cp, int n, struct uio *uio);
 int	uiomove_frombuf(void *buf, int buflen, struct uio *uio);
 int	uiomove_fromphys(struct vm_page *ma[], vm_offset_t offset, int n,