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

[Marc-André Lureau]

On Fri, May 19, 2017 at 4:49 PM Anton Nefedov <address@hidden>
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 <address@hidden>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>

I would move this patch up in the series, otherwise looks good


> ---
>  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
>
>
> --
Marc-André Lureau