char-fe: implement qemu_chr_fe_backend_name

A number of chardev users where calling qemu_chr_fe_get_driver() which
is discouraged as it blocks backend hotswap. As the pattern is common
and need for the string is transitory add a helper and keep
qemu_chr_fe_get_driver() for those that really need the funkiness of
poking around the backend setup.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20260824-fixes-for-11-2-v2-4-352c6b890402@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

3 files changed, 3 insertions, 21 deletions

diff --git a/backends/cryptodev-vhost-user.c b/backends/cryptodev-vhost-user.c
index cc478d9902..3334e280a2 100644
--- a/backends/cryptodev-vhost-user.c
+++ b/backends/cryptodev-vhost-user.c
@@ -373,13 +373,7 @@ cryptodev_vhost_user_get_chardev(Object *obj, Error **errp)
 {
     CryptoDevBackendVhostUser *s =
                       CRYPTODEV_BACKEND_VHOST_USER(obj);
-    Chardev *chr = qemu_chr_fe_get_driver(&s->chr);
-
-    if (chr && chr->label) {
-        return g_strdup(chr->label);
-    }
-
-    return NULL;
+    return qemu_chr_fe_backend_name(&s->chr);
 }
 
 static void cryptodev_vhost_user_finalize(Object *obj)
diff --git a/backends/rng-egd.c b/backends/rng-egd.c
index 1d92bd71cf..c2207f40c5 100644
--- a/backends/rng-egd.c
+++ b/backends/rng-egd.c
@@ -126,13 +126,7 @@ static void rng_egd_set_chardev(Object *obj, const char *value, Error **errp)
 static char *rng_egd_get_chardev(Object *obj, Error **errp)
 {
     RngEgd *s = RNG_EGD(obj);
-    Chardev *chr = qemu_chr_fe_get_driver(&s->chr);
-
-    if (chr && chr->label) {
-        return g_strdup(chr->label);
-    }
-
-    return NULL;
+    return qemu_chr_fe_backend_name(&s->chr);
 }
 
 static void rng_egd_finalize(Object *obj)
diff --git a/backends/vhost-user.c b/backends/vhost-user.c
index 380d825023..46dadb7480 100644
--- a/backends/vhost-user.c
+++ b/backends/vhost-user.c
@@ -152,13 +152,7 @@ static void set_chardev(Object *obj, const char *value, Error **errp)
 static char *get_chardev(Object *obj, Error **errp)
 {
     VhostUserBackend *b = VHOST_USER_BACKEND(obj);
-    Chardev *chr = qemu_chr_fe_get_driver(&b->chr);
-
-    if (chr && chr->label) {
-        return g_strdup(chr->label);
-    }
-
-    return NULL;
+    return qemu_chr_fe_backend_name(&b->chr);
 }
 
 static void vhost_user_backend_class_init(ObjectClass *oc, const void *data)