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 <anton.nefedov@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 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 ba1a5f5..1eed934 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 qemu_chr_fe_connect(CharBackend *b, Chardev *s, Error **errp)
 {
     int tag = 0;
diff --git a/include/sysemu/char.h b/include/sysemu/char.h
index 014ebbc..117d628 100644
--- a/include/sysemu/char.h
+++ b/include/sysemu/char.h
@@ -391,10 +391,20 @@ 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

On Tue, May 30, 2017 at 6:13 PM Anton Nefedov <anton.nefedov@virtuozzo.com>
wrote:

> 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 <anton.nefedov@virtuozzo.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>


> ---
>  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 ba1a5f5..1eed934 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 qemu_chr_fe_connect(CharBackend *b, Chardev *s, Error **errp)
>  {
>      int tag = 0;
> diff --git a/include/sysemu/char.h b/include/sysemu/char.h
> index 014ebbc..117d628 100644
> --- a/include/sysemu/char.h
> +++ b/include/sysemu/char.h
> @@ -391,10 +391,20 @@ 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
>
>
> --
Marc-André Lureau