[RFC PATCH] 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.

Signed-off-by: Alex Bennée <[email protected]>
Suggested-by: Peter Maydell <[email protected]>
---
 include/chardev/char-fe.h       | 13 ++++++++++++-
 backends/cryptodev-vhost-user.c |  8 +-------
 backends/rng-egd.c              |  8 +-------
 backends/vhost-user.c           |  8 +-------
 hw/char/imx_serial.c            |  4 ++--
 5 files changed, 17 insertions(+), 24 deletions(-)

diff --git a/include/chardev/char-fe.h b/include/chardev/char-fe.h
index 5f8a6df17dc..13218d04c8d 100644
--- a/include/chardev/char-fe.h
+++ b/include/chardev/char-fe.h
@@ -52,7 +52,8 @@ void qemu_chr_fe_deinit(CharFrontend *c, bool del);
  * associated Chardev.
  * Note: avoid this function as the driver should never be accessed directly,
  *       especially by the frontends that support chardevice hotswap.
- *       Consider qemu_chr_fe_backend_connected() to check for driver existence
+ *       Consider qemu_chr_fe_backend_connected() to check for driver
+ *       existence or qemu_chr_fe_backend_name() if you need the name.
  */
 Chardev *qemu_chr_fe_get_driver(CharFrontend *c);
 
@@ -70,6 +71,16 @@ bool qemu_chr_fe_backend_connected(CharFrontend *c);
  */
 bool qemu_chr_fe_backend_open(CharFrontend *c);
 
+/**
+  * qemu_chr_fe_backend_name:
+  *
+  * Returns: caller freeable string or NULL
+  */
+static inline char * qemu_chr_fe_backend_name(CharFrontend *c)
+{
+    return (c->chr && c->chr->label) ? g_strdup(c->chr->label) : NULL;
+}
+
 /**
  * qemu_chr_fe_set_handlers_full:
  * @c: a CharFrontend
diff --git a/backends/cryptodev-vhost-user.c b/backends/cryptodev-vhost-user.c
index cc478d9902d..3334e280a27 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 1d92bd71cf7..c2207f40c5c 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 380d8250233..46dadb74800 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)
diff --git a/hw/char/imx_serial.c b/hw/char/imx_serial.c
index fb41ee2ac50..8ac4efbb5e9 100644
--- a/hw/char/imx_serial.c
+++ b/hw/char/imx_serial.c
@@ -278,10 +278,10 @@ static void imx_serial_write(void *opaque, hwaddr offset,
                              uint64_t value, unsigned size)
 {
     IMXSerialState *s = (IMXSerialState *)opaque;
-    Chardev *chr = qemu_chr_fe_get_driver(&s->chr);
+    g_autofree char *label = qemu_chr_fe_backend_name(&s->chr);
     unsigned char ch;
 
-    trace_imx_serial_write(chr ? chr->label : "NODEV", offset, value);
+    trace_imx_serial_write(label ? label : "NODEV", offset, value);
 
     switch (offset >> 2) {
     case 0x10: /* UTXD */
-- 
2.47.3