From: Yuxue Liu <yuxue.liu@jaguarmicro.com>

In the scenario where vhost-user sets eventfd to -1,
qemu_chr_fe_get_msgfds retrieves fd as -1. When vhost_user_read
receives, it does not perform blocking operations on the descriptor
with fd=-1, so non-blocking operations should not be performed here
either.This is a normal use case. Calling g_unix_set_fd_nonblocking
at this point will cause the test to interrupt.

When vhost_user_write sets the call fd to -1, it sets the number of
fds to 0, so the fds obtained by qemu_chr_fe_get_msgfds will also
be 0.

Signed-off-by: Yuxue Liu <yuxue.liu@jaguarmicro.com>
Message-Id: <20240411073555.1357-1-yuxue.liu@jaguarmicro.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit f72fc16910c8f44edf052f52672e0e63bbbc773c)
(Mjt: pick this trivial focused change up for 7.2.x so that subsequent change(s) in this area apply cleanly)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/tests/qtest/vhost-user-test.c b/tests/qtest/vhost-user-test.c
index e4f95b2858..6d9e53ff07 100644
--- a/tests/qtest/vhost-user-test.c
+++ b/tests/qtest/vhost-user-test.c
@@ -456,7 +456,10 @@ static void chr_read(void *opaque, const uint8_t *buf, int size)
     case VHOST_USER_SET_VRING_KICK:
     case VHOST_USER_SET_VRING_CALL:
         /* consume the fd */
-        qemu_chr_fe_get_msgfds(chr, &fd, 1);
+        if (!qemu_chr_fe_get_msgfds(chr, &fd, 1) && fd < 0) {
+            qos_printf("call fd: %d, do not set non-blocking\n", fd);
+            break;
+        }
         /*
          * This is a non-blocking eventfd.
          * The receive function forces it to be blocking,
-- 
2.47.3