Re: [PATCH 6/8] plugins: implement QPP import function

[Alex Bennée]

Andrew Fasano <fasano@mit.edu> writes:

> From: Elysia Witham <elysia.witham@ll.mit.edu>
>
> Plugins can export functions or import functions from other
> plugins using their name and the function name. This is also
> described in <qemu-plugin.h>.
>
> Signed-off-by: Elysia Witham <elysia.witham@ll.mit.edu>
> Signed-off-by: Andrew Fasano <fasano@mit.edu>
> ---
>  include/qemu/qemu-plugin.h   | 10 ++++++++++
>  plugins/api.c                | 21 +++++++++++++++++++++
>  plugins/qemu-plugins.symbols |  1 +
>  3 files changed, 32 insertions(+)
>
> diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
> index 4221545015..a0516e9a0e 100644
> --- a/include/qemu/qemu-plugin.h
> +++ b/include/qemu/qemu-plugin.h
> @@ -354,6 +354,16 @@ size_t qemu_plugin_tb_n_insns(const struct 
> qemu_plugin_tb *tb);
>   */
>  uint64_t qemu_plugin_tb_vaddr(const struct qemu_plugin_tb *tb);
>  
> +/**
> + * qemu_plugin_import_function() - return pointer to a function in another
> + * plugin
> + * @plugin: plugin name
> + * @function: function name
> + *
> + * Returns: NULL on failure, function pointer on success
> + */
> +gpointer qemu_plugin_import_function(const char *plugin, const char 
> *function);
> +
>  /**
>   * qemu_plugin_create_callback() - create a new cb with given name
>   * @id: unique plugin id
> diff --git a/plugins/api.c b/plugins/api.c
> index 1f7ea718dc..a998df6942 100644
> --- a/plugins/api.c
> +++ b/plugins/api.c
> @@ -400,6 +400,27 @@ bool qemu_plugin_bool_parse(const char *name, const char 
> *value, bool *ret)
>      return name && value && qapi_bool_parse(name, value, ret, NULL);
>  }
>  
> +/*
> + * QPP: inter-plugin function resolution and callbacks
> + */
> +
> +gpointer qemu_plugin_import_function(const char *target_plugin,
> +                                     const char *function) {
> +    gpointer function_pointer = NULL;
> +    struct qemu_plugin_ctx *ctx = plugin_name_to_ctx_locked(target_plugin);
> +    if (ctx == NULL) {
> +        error_report("Unable to load plugin %s by name", target_plugin);
> +    } else if (g_module_symbol(ctx->handle, function,
> +               (gpointer *)&function_pointer)) {
> +        return function_pointer;
> +    } else {
> +      error_report("function: %s not found in plugin: %s", function,
> +                   target_plugin);
> +    }
> +    abort();
> +    return NULL;

Hmm when does __attribute__ ((constructor)) get called during the
g_module_open() of the plugin? I think aborting is a is a poor failure
mode in this case as you can bring down the whole translator with a poor
plugin load. I'd rather fail gracefully and uninstall the plugin.

> +}
> +
>  bool qemu_plugin_create_callback(qemu_plugin_id_t id, const char *cb_name)
>  {
>      struct qemu_plugin_ctx *ctx = plugin_id_to_ctx_locked(id);
> diff --git a/plugins/qemu-plugins.symbols b/plugins/qemu-plugins.symbols
> index b7013980cf..70a518839d 100644
> --- a/plugins/qemu-plugins.symbols
> +++ b/plugins/qemu-plugins.symbols
> @@ -3,6 +3,7 @@
>    qemu_plugin_end_code;
>    qemu_plugin_entry_code;
>    qemu_plugin_get_hwaddr;
> +  qemu_plugin_import_function;
>    qemu_plugin_create_callback;
>    qemu_plugin_run_callback;
>    qemu_plugin_reg_callback;


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro