[Qemu-devel] [PATCH v2 5/9] char: forbid direct chardevice access for hotswap devices

[Anton Nefedov]

qemu_chr_fe_get_driver() is unsafe, frontends with hotswap support
should not access CharDriver ptr directly as CharDriver might change.

Signed-off-by: Anton Nefedov <address@hidden>
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
 chardev/char.c        |  7 +++++++
 include/sysemu/char.h | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/chardev/char.c b/chardev/char.c
index 0483f19..36d6f36 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -484,9 +484,16 @@ static Notifier muxes_realize_notify = {
 
 Chardev *qemu_chr_fe_get_driver(CharBackend *be)
 {
+    /* this is unsafe for the users that support chardev hotswap */
+    assert(be->chr_be_change == NULL);
     return be->chr;
 }
 
+bool qemu_chr_fe_backend_connected(CharBackend *be)
+{
+    return !!be->chr;
+}
+
 static bool fe_connect(CharBackend *b, Chardev *s, Error **errp)
 {
     int tag = 0;
diff --git a/include/sysemu/char.h b/include/sysemu/char.h
index 92ae57e..fa21535 100644
--- a/include/sysemu/char.h
+++ b/include/sysemu/char.h
@@ -404,10 +404,20 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error 
**errp);
  *
  * Returns the driver associated with a CharBackend or NULL if no
  * 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
  */
 Chardev *qemu_chr_fe_get_driver(CharBackend *be);
 
 /**
+ * @qemu_chr_fe_backend_connected:
+ *
+ * Returns true if there is a chardevice associated with @be.
+ */
+bool qemu_chr_fe_backend_connected(CharBackend *be);
+
+/**
  * @qemu_chr_fe_deinit:
  *
  * Dissociate the CharBackend from the Chardev.
-- 
2.7.4