Re: [Qemu-devel] [PATCH v10 5/8] module: implement module loading

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Sep 16, 2013 at 02:50:24PM +0800, Fam Zheng wrote:
> Added three types of modules:
> 
>     typedef enum {
>         MODULE_LOAD_BLOCK = 0,
>         MODULE_LOAD_UI,
>         MODULE_LOAD_NET,
>         MODULE_LOAD_MAX,
>     } module_load_type;
> 
> and their loading function:
> 
>     void module_load(module_load_type).
> 
> which loads whitelisted ".so" files of the given type under ${MODDIR}.
> 
> Modules of each type should be loaded in respective subsystem
> initialization code.
> 
> The init function of dynamic module is no longer with
> __attribute__((constructor)) as static linked version, and need to be
> explicitly called once loaded. The function name is mangled with per
> configure fingerprint as:
> 
>     init_$(date +%s$$$RANDOM)
> 
> Which is known to module_load function, and the loading fails if this
> symbol is not there. With this, modules built from a different
> tree/version/configure will not be loaded.
> 
> The module loading code requires gmodule-2.0.
> 
> Configure option "--enable-modules=L" can be used to restrict qemu to
> only build/load some whitelisted modules.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  Makefile              |  3 ++
>  block.c               |  1 +
>  configure             | 44 +++++++++++++++++++++-------
>  include/qemu/module.h | 23 +++++++++++++++
>  rules.mak             |  9 ++++--
>  scripts/create_config | 22 ++++++++++++++
>  util/module.c         | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  vl.c                  |  2 ++
>  8 files changed, 172 insertions(+), 13 deletions(-)
> 
> +void module_load(module_load_type type)
> +{
> +#ifdef CONFIG_MODULES
> +    const char *prefix;
> +    char *fname = NULL;
> +    const char **mp;
> +    static const char *module_whitelist[] = {
> +        CONFIG_MODULE_WHITELIST
> +    };
> +
> +    if (!g_module_supported()) {
> +        return;
> +    }
> +
> +    switch (type) {
> +    case MODULE_LOAD_BLOCK:
> +        prefix = "block-";
> +        break;
> +    case MODULE_LOAD_UI:
> +        prefix = "ui-";
> +        break;
> +    case MODULE_LOAD_NET:
> +        prefix = "ui-";

Wrong prefix.

> +        break;
> +    default:
> +        return;
> +    }
> +
> +    for (mp = &module_whitelist[0]; *mp; mp++) {
> +        if (strncmp(prefix, *mp, strlen(prefix))) {
> +            continue;
> +        }
> +        fname = g_strdup_printf("%s/%s%s", CONFIG_MODDIR, *mp, HOST_DSOSUF);
> +        module_load_file(fname);
> +        g_free(fname);
> +    }
> +
> +#endif
> +}

IMHO this method design is really crazy. If you want to have a
situation where you call module_load() multiple times, then
have separate whitelists for block/net/ui, instead of having
one global whitelist which you then have to load a subset of
each time.  Alternatively just call module_load() once and
give rid of these enums for loading block/net/ui separately.

Daniel
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