Replace virtio_error() with a macro that automatically prepends the
calling function name to error messages. This provides better context
for debugging virtio issues by showing exactly which function
encountered the error.

Before: "Invalid queue size: 1024"
After:  "virtio_queue_set_num: Invalid queue size: 1024"

The implementation uses a macro to insert __func__ at compile time,
avoiding any runtime overhead while providing more specific error
context than a generic "virtio:" prefix.

Also remove manual __func__ usage in virtio-balloon to avoid duplicate
function names in error messages.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/230
Buglink: https://bugs.launchpad.net/qemu/+bug/1919021

Signed-off-by: Alessandro Ratti <alessandro@0x65c.net>
---
 hw/virtio/virtio-balloon.c | 2 +-
 hw/virtio/virtio.c         | 2 +-
 include/hw/virtio/virtio.h | 4 +++-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index db787d00b3..e443f71c01 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -697,7 +697,7 @@ virtio_balloon_free_page_hint_notify(NotifierWithReturn *n, void *data,
     case PRECOPY_NOTIFY_COMPLETE:
         break;
     default:
-        virtio_error(vdev, "%s: %d reason unknown", __func__, pnd->reason);
+        virtio_error(vdev, "%d reason unknown", pnd->reason);
     }
 
     return 0;
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 9a81ad912e..44528d7f2b 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -3931,7 +3931,7 @@ void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name)
     vdev->bus_name = g_strdup(bus_name);
 }
 
-void G_GNUC_PRINTF(2, 3) virtio_error(VirtIODevice *vdev, const char *fmt, ...)
+void G_GNUC_PRINTF(2, 3) virtio_error_impl(VirtIODevice *vdev, const char *fmt, ...)
 {
     va_list ap;
 
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index c594764f23..961d021497 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -249,7 +249,9 @@ void virtio_init(VirtIODevice *vdev, uint16_t device_id, size_t config_size);
 
 void virtio_cleanup(VirtIODevice *vdev);
 
-void virtio_error(VirtIODevice *vdev, const char *fmt, ...) G_GNUC_PRINTF(2, 3);
+#define virtio_error(vdev, fmt, ...) \
+    virtio_error_impl(vdev, "%s: " fmt, __func__, ##__VA_ARGS__)
+void virtio_error_impl(VirtIODevice *vdev, const char *fmt, ...) G_GNUC_PRINTF(2, 3);
 
 /* Set the child bus name. */
 void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name);
-- 
2.39.5