Re: [PATCH 11/12] vu_common: Prepare to use multibuffer with guest RX

2 Mar 2026

On Fri, Feb 27, 2026 at 03:03:29PM +0100, Laurent Vivier wrote:
...
1b95bd6fa114 ("vhost_user: fix multibuffer from linux") introduces
multibuffer with TX (from the guest), but with iPXE we need to handle
also multibuffer for RX (to the guest). This patch makes the parameter
generic and global.
No functional change.
Signed-off-by: Laurent Vivier 
Reviewed-by: David Gibson 

In the sense that it does what it says on the tin.

Am I right in thinking this will only allow at most two buffers per
element for both to-guest and from-guest paths?  Having a fixed number
of buffers per element for the from-guest path seems a bit fragile.
...
---
 vu_common.c | 6 ++----
 vu_common.h | 2 ++
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/vu_common.c b/vu_common.c
index e32a56d881a3..67d8f3e47338 100644
--- a/vu_common.c
+++ b/vu_common.c
@@ -20,8 +20,6 @@
 #include "migrate.h"
 #include "epoll_ctl.h"
-#define VU_MAX_TX_BUFFER_NB	2
-
 /**
  * vu_packet_check_range() - Check if a given memory zone is contained in
  * 			     a mapped guest memory region
@@ -184,11 +182,11 @@ static void vu_handle_tx(struct vu_dev *vdev, int index,
  count = 0;
  out_sg_count = 0;
  while (count < ARRAY_SIZE(elem) &&
-	       out_sg_count + VU_MAX_TX_BUFFER_NB <= VIRTQUEUE_MAX_SIZE) {
+	       out_sg_count + IOV_PER_ELEM <= VIRTQUEUE_MAX_SIZE) {
      int ret;
      struct iov_tail data;
-		elem[count].out_num = VU_MAX_TX_BUFFER_NB;
+		elem[count].out_num = IOV_PER_ELEM;
      elem[count].out_sg = &out_sg[out_sg_count];
      elem[count].in_num = 0;
      elem[count].in_sg = NULL;
diff --git a/vu_common.h b/vu_common.h
index 51639c04df14..2c2d11abb26f 100644
--- a/vu_common.h
+++ b/vu_common.h
@@ -9,6 +9,8 @@
 #define VU_COMMON_H
 #include 
+#define IOV_PER_ELEM	(2)
+
 static inline void *vu_eth(void *base)
 {
  return ((char *)base + VNET_HLEN);
-- 
2.53.0
-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

    