Re: [Qemu-devel] [Qemu-block] [PATCH 3/3] blockdev: Add dynamic module loading for block drivers

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, Jun 22, 2016 at 05:35:54PM -0400, Colin Lord wrote:
> +    for (i = 0; i < ARRAY_SIZE(block_driver_modules); ++i) {
> +        if (!strcmp(block_driver_modules[i].format_name, format_name)) {
> +            block_module_load_one(block_driver_modules[i].library_name);
> +            /* Copying code is not nice, but this way the current discovery is
> +             * not modified. Calling recursively could fail if the library
> +             * has been deleted.
> +             */
> +            QLIST_FOREACH(drv1, &bdrv_drivers, list) {
> +                if (!strcmp(drv1->format_name, format_name)) {
> +                    return drv1;
> +                }
> +            }
> +        }
> +    }
> +
>      return NULL;
>  }

No recursion:

static BlockDriver *bdrv_do_find_format(const char *format_name)
{
    BlockDriver *drv1;

    QLIST_FOREACH(drv1, &bdrv_drivers, list) {
        if (!strcmp(drv1->format_name, format_name)) {
            return drv1;
        }
    }

    return NULL;
}

BlockDriver *bdrv_find_format(const char *format_name)
{
    BlockDriver *drv;
    size_t i;

    drv = bdrv_do_find_format(format_name);
    if (drv) {
        return drv;
    }

    /* The driver isn't registered, maybe we need to load a module */
    for (i = 0; i < ARRAY_SIZE(block_driver_modules); ++i) {
        if (!strcmp(block_driver_modules[i].format_name, format_name)) {
            block_module_load_one(block_driver_modules[i].library_name);
	    break;
        }
    }
    return bdrv_do_find_format(format_name);
}

>  
> @@ -447,8 +466,15 @@ int get_tmp_filename(char *filename, int size)
>  static BlockDriver *find_hdev_driver(const char *filename)
>  {
>      int score_max = 0, score;
> +    size_t i;
>      BlockDriver *drv = NULL, *d;
>  
> +    for (i = 0; i < ARRAY_SIZE(block_driver_modules); ++i) {
> +        if (block_driver_modules[i].has_probe_device) {
> +            block_module_load_one(block_driver_modules[i].library_name);
> +        }
> +    }

This patch series needs to solve probing so that we don't end up loading
all block drivers.  Fam's suggestion for a built-in probe.c sounds good
to me.

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