Index: uipc_socket.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_socket.c,v
diff -u -p -r1.344 uipc_socket.c
--- uipc_socket.c	31 Oct 2024 12:51:55 -0000	1.344
+++ uipc_socket.c	1 Nov 2024 23:53:25 -0000
@@ -787,48 +787,36 @@ m_getuio(struct mbuf **mp, int atomic, l
 {
 	struct mbuf *m, *top = NULL;
 	struct mbuf **nextp = ⊤
-	u_long len, mlen;
-	size_t resid = uio->uio_resid;
+	u_long len, mlen, alen;
+	int align = atomic ? roundup(max_hdr, sizeof(long)) : 0;
 	int error;
 
-	do {
-		if (top == NULL) {
-			MGETHDR(m, M_WAIT, MT_DATA);
-			mlen = MHLEN;
-		} else {
-			MGET(m, M_WAIT, MT_DATA);
-			mlen = MLEN;
-		}
+	m = m_gethdr(M_WAIT, MT_DATA);
+	mlen = MHLEN;
+
+	for (;;) {
 		/* chain mbuf together */
 		*nextp = m;
 		nextp = &m->m_next;
 
-		resid = ulmin(resid, space);
-		if (resid >= MINCLSIZE) {
-			MCLGETL(m, M_NOWAIT, ulmin(resid, MAXMCLBYTES));
-			if ((m->m_flags & M_EXT) == 0)
+		/* How much data we want to put in this mbuf? */
+		len = ulmin(uio->uio_resid, space);
+		/* How much space are we allocating for that data? */
+		alen = align + len;
+		if (alen > mlen) {
+			MCLGETL(m, M_NOWAIT, ulmin(alen, MAXMCLBYTES));
+			if (!ISSET(m->m_flags, M_EXT) && alen > MCLBYTES)
 				MCLGETL(m, M_NOWAIT, MCLBYTES);
-			if ((m->m_flags & M_EXT) == 0)
-				goto nopages;
-			mlen = m->m_ext.ext_size;
-			len = ulmin(mlen, resid);
-			/*
-			 * For datagram protocols, leave room
-			 * for protocol headers in first mbuf.
-			 */
-			if (atomic && m == top && len < mlen - max_hdr)
-				m->m_data += max_hdr;
-		} else {
-nopages:
-			len = ulmin(mlen, resid);
-			/*
-			 * For datagram protocols, leave room
-			 * for protocol headers in first mbuf.
-			 */
-			if (atomic && m == top && len < mlen - max_hdr)
-				m_align(m, len);
+			if (ISSET(m->m_flags, M_EXT))
+				mlen = m->m_ext.ext_size;
 		}
 
+		/* Avoid pain from a stupid max_hdr value */
+		if (align < mlen)
+			m->m_data += align;
+
+		/* How much data can we put in this mbuf? */
+		len = ulmin(mlen, len);
 		error = uiomove(mtod(m, caddr_t), len, uio);
 		if (error) {
 			m_freem(top);
@@ -836,13 +824,19 @@ nopages:
 		}
 
 		/* adjust counters */
-		resid = uio->uio_resid;
 		space -= len;
 		m->m_len = len;
 		top->m_pkthdr.len += len;
 
 		/* Is there more space and more data? */
-	} while (space > 0 && resid > 0);
+		if (space == 0 || uio->uio_resid == 0)
+			break;
+
+		align = 0;
+
+		m = m_get(M_WAIT, MT_DATA);
+		mlen = MLEN;
+	}
 
 	*mp = top;
 	return 0;