This reverts commit 46d4d36d0bf2b24b205f2f604f0905db80264eef.

The reverted commit changed to emit warnings instead of errors when
vhost is requested but vhost initialization fails if vhostforce option
is not set.

However, vhostforce is not meant to change the error handling. It was
once introduced as an option to commit 5430a28fe4 ("vhost: force vhost
off for non-MSI guests") to force enabling vhost for non-MSI guests,
which will have worse performance with vhost. It was deprecated with
commit 1e7398a140 ("vhost: enable vhost without without MSI-X") and
changed to behave identical with the vhost option for compatibility.

Worse, commit bf769f742c ("virtio: del net client if net_init_tap_one
failed") changed to delete the client when vhost fails even when the
failure only results in a warning. The leads to an assertion failure
for the -netdev command line option.

The reverted commit was intended to ensure that the vhost initialization
failure won't result in a corrupted netdev. This problem should have
been fixed by deleting netdev when the initialization fails instead of
ignoring the failure by converting it into a warning. Fortunately,
commit bf769f742c ("virtio: del net client if net_init_tap_one failed"),
mentioned earlier, implements this behavior.

Restore the correct semantics and fix the assertion failure for the
-netdev command line option by reverting the problematic commit.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
V1 -> V2: Corrected the message.

 include/net/vhost_net.h |  3 ---
 net/tap.c               | 22 +++++-----------------
 2 files changed, 5 insertions(+), 20 deletions(-)

diff --git a/include/net/vhost_net.h b/include/net/vhost_net.h
index c37aba35e6..c6a5361a2a 100644
--- a/include/net/vhost_net.h
+++ b/include/net/vhost_net.h
@@ -4,9 +4,6 @@
 #include "net/net.h"
 #include "hw/virtio/vhost-backend.h"
 
-#define VHOST_NET_INIT_FAILED \
-    "vhost-net requested but could not be initialized"
-
 struct vhost_net;
 typedef struct vhost_net VHostNetState;
 
diff --git a/net/tap.c b/net/tap.c
index 1bf085d422..c6639d9f20 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -730,11 +730,7 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
         if (vhostfdname) {
             vhostfd = monitor_fd_param(monitor_cur(), vhostfdname, &err);
             if (vhostfd == -1) {
-                if (tap->has_vhostforce && tap->vhostforce) {
-                    error_propagate(errp, err);
-                } else {
-                    warn_report_err(err);
-                }
+                error_propagate(errp, err);
                 goto failed;
             }
             if (!g_unix_set_fd_nonblocking(vhostfd, true, NULL)) {
@@ -745,13 +741,8 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
         } else {
             vhostfd = open("/dev/vhost-net", O_RDWR);
             if (vhostfd < 0) {
-                if (tap->has_vhostforce && tap->vhostforce) {
-                    error_setg_errno(errp, errno,
-                                     "tap: open vhost char device failed");
-                } else {
-                    warn_report("tap: open vhost char device failed: %s",
-                                strerror(errno));
-                }
+                error_setg_errno(errp, errno,
+                                 "tap: open vhost char device failed");
                 goto failed;
             }
             if (!g_unix_set_fd_nonblocking(vhostfd, true, NULL)) {
@@ -764,11 +755,8 @@ static void net_init_tap_one(const NetdevTapOptions *tap, NetClientState *peer,
 
         s->vhost_net = vhost_net_init(&options);
         if (!s->vhost_net) {
-            if (tap->has_vhostforce && tap->vhostforce) {
-                error_setg(errp, VHOST_NET_INIT_FAILED);
-            } else {
-                warn_report(VHOST_NET_INIT_FAILED);
-            }
+            error_setg(errp,
+                       "vhost-net requested but could not be initialized");
             goto failed;
         }
     } else if (vhostfdname) {
-- 
2.42.0

On Thu, Sep 21, 2023 at 5:48 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>
> This reverts commit 46d4d36d0bf2b24b205f2f604f0905db80264eef.
>
> The reverted commit changed to emit warnings instead of errors when
> vhost is requested but vhost initialization fails if vhostforce option
> is not set.
>
> However, vhostforce is not meant to change the error handling. It was
> once introduced as an option to commit 5430a28fe4 ("vhost: force vhost
> off for non-MSI guests") to force enabling vhost for non-MSI guests,
> which will have worse performance with vhost. It was deprecated with
> commit 1e7398a140 ("vhost: enable vhost without without MSI-X") and
> changed to behave identical with the vhost option for compatibility.
>
> Worse, commit bf769f742c ("virtio: del net client if net_init_tap_one
> failed") changed to delete the client when vhost fails even when the
> failure only results in a warning. The leads to an assertion failure
> for the -netdev command line option.
>
> The reverted commit was intended to ensure that the vhost initialization
> failure won't result in a corrupted netdev. This problem should have
> been fixed by deleting netdev when the initialization fails instead of
> ignoring the failure by converting it into a warning. Fortunately,
> commit bf769f742c ("virtio: del net client if net_init_tap_one failed"),
> mentioned earlier, implements this behavior.
>
> Restore the correct semantics and fix the assertion failure for the
> -netdev command line option by reverting the problematic commit.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
> V1 -> V2: Corrected the message.
>

Queued.

Thanks