On Wed, 5 Aug 2015 09:46:41 -0400 Dan Streetman <ddstreet@xxxxxxxx> wrote:
> Add zpool_has_pool() function, indicating if the specified type of zpool
> is available (i.e. zsmalloc or zbud). This allows checking if a pool is
> available, without actually trying to allocate it, similar to
> crypto_has_alg().
>
> This is used by a following patch to zswap that enables the dynamic
> runtime creation of zswap zpools.
>
> ...
>
> /**
> + * zpool_has_pool() - Check if the pool driver is available
> + * @type The type of the zpool to check (e.g. zbud, zsmalloc)
> + *
> + * This checks if the @type pool driver is available.
> + *
> + * Returns: true if @type pool is available, false if not
> + */
> +bool zpool_has_pool(char *type)
> +{
> + struct zpool_driver *driver = zpool_get_driver(type);
> +
> + if (!driver) {
> + request_module("zpool-%s", type);
> + driver = zpool_get_driver(type);
> + }
> +
> + if (!driver)
> + return false;
> +
> + zpool_put_driver(driver);
> + return true;
> +}
This looks racy: after that zpool_put_driver() has completed, an rmmod
will invalidate zpool_has_pool()'s return value.
If there's some reason why this can't happen, can we please have a code
comment which reveals that reason?
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