hw: Make qdev_get_printable_name() consistently return freeable string

The current implementation of qdev_get_printable_name() sometimes
returns a string that must not be freed (vdev->id or the fixed
fallback string "<unknown device>" and sometimes returns a string
that must be freed (the return value of qdev_get_dev_path()). This
forces callers to leak the string in the "must be freed" case.

Make the function consistent that it always returns a string that
the caller must free, and make the three callsites free it.

This fixes leaks like this that show up when running "make check"
with the address sanitizer enabled:

Direct leak of 13 byte(s) in 1 object(s) allocated from:
    #0 0x5561de21f293 in malloc (/home/pm215/qemu/build/san/qemu-system-i386+0x1a2d293) (BuildId: 6d6fad7130fd5c8dbbc03401df554f68b8034936)
    #1 0x767ad7a82ac9 in g_malloc (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x62ac9) (BuildId: 116e142b9b52c8a4dfd403e759e71ab8f95d8bb3)
    #2 0x5561deaf34f2 in pcibus_get_dev_path /home/pm215/qemu/build/san/../../hw/pci/pci.c:2792:12
    #3 0x5561df9d8830 in qdev_get_printable_name /home/pm215/qemu/build/san/../../hw/core/qdev.c:431:24
    #4 0x5561deebdca2 in virtio_init_region_cache /home/pm215/qemu/build/san/../../hw/virtio/virtio.c:298:17
    #5 0x5561df05f842 in memory_region_write_accessor /home/pm215/qemu/build/san/../../system/memory.c:491:5
    #6 0x5561df05ed1b in access_with_adjusted_size /home/pm215/qemu/build/san/../../system/memory.c:567:18
    #7 0x5561df05e3fa in memory_region_dispatch_write /home/pm215/qemu/build/san/../../system/memory.c
    #8 0x5561df0aa805 in address_space_stm_internal /home/pm215/qemu/build/san/../../system/memory_ldst.c.inc:85:13
    #9 0x5561df0bcad3 in qtest_process_command /home/pm215/qemu/build/san/../../system/qtest.c:480:13

Cc: qemu-stable@nongnu.org
Fixes: e209d4d7a3 ("virtio: improve virtqueue mapping error messages")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20260307155046.3940197-3-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/core/qdev.c

@@ -420,7 +420,7 @@ const char *qdev_get_printable_name(DeviceState *vdev)
      * names.
      */
     if (vdev->id) {
-        return vdev->id;
+        return g_strdup(vdev->id);
     }
     /*
      * Fall back to the canonical QOM device path (eg. ID for PCI
@@ -437,7 +437,7 @@ const char *qdev_get_printable_name(DeviceState *vdev)
      * Final fallback: if all else fails, return a placeholder string.
      * This ensures the error message always contains a valid string.
      */
-    return "<unknown device>";
+    return g_strdup("<unknown device>");
 }
 
 void qdev_add_unplug_blocker(DeviceState *dev, Error *reason)

hw/virtio/virtio.c

@@ -281,10 +281,12 @@ void virtio_init_region_cache(VirtIODevice *vdev, int n)
     len = address_space_cache_init(&new->desc, vdev->dma_as,
                                    addr, size, packed);
     if (len < size) {
+        g_autofree const char *devname = qdev_get_printable_name(DEVICE(vdev));
+
         virtio_error(vdev,
                 "Failed to map descriptor ring for device %s: "
                 "invalid guest physical address or corrupted queue setup",
-                qdev_get_printable_name(DEVICE(vdev)));
+                devname);
         goto err_desc;
     }
 
@@ -292,10 +294,12 @@ void virtio_init_region_cache(VirtIODevice *vdev, int n)
     len = address_space_cache_init(&new->used, vdev->dma_as,
                                    vq->vring.used, size, true);
     if (len < size) {
+        g_autofree const char *devname = qdev_get_printable_name(DEVICE(vdev));
+
         virtio_error(vdev,
                 "Failed to map used ring for device %s: "
                 "possible guest misconfiguration or insufficient memory",
-                qdev_get_printable_name(DEVICE(vdev)));
+                devname);
         goto err_used;
     }
 
@@ -303,10 +307,12 @@ void virtio_init_region_cache(VirtIODevice *vdev, int n)
     len = address_space_cache_init(&new->avail, vdev->dma_as,
                                    vq->vring.avail, size, false);
     if (len < size) {
+        g_autofree const char *devname = qdev_get_printable_name(DEVICE(vdev));
+
         virtio_error(vdev,
                 "Failed to map avalaible ring for device %s: "
                 "possible queue misconfiguration or overlapping memory region",
-                qdev_get_printable_name(DEVICE(vdev)));
+                devname);
         goto err_avail;
     }
 

include/hw/core/qdev.h

@@ -1084,6 +1084,22 @@ extern bool qdev_hot_removed;
  * If @dev is NULL or not on a bus, returns NULL.
  */
 char *qdev_get_dev_path(DeviceState *dev);
+
+/**
+ * qdev_get_printable_name: Return human readable name for device
+ * @dev: Device to get name of
+ *
+ * Returns: A newly allocated string containing some human
+ * readable name for the device, suitable for printing in
+ * user-facing error messages. The function will never return NULL,
+ * so the name can be used without further checking or fallbacks.
+ *
+ * If the device has an explicitly set ID (e.g. by the user on the
+ * command line via "-device thisdev,id=myid") this is preferred.
+ * Otherwise we try the canonical QOM device path (which will be
+ * the PCI ID for PCI devices, for example). If all else fails
+ * we will return the placeholder "<unknown device">.
+ */
 const char *qdev_get_printable_name(DeviceState *dev);
 
 void qbus_set_hotplug_handler(BusState *bus, Object *handler);