[PATCH 1/3] zpool: add zpool_has_pool()

[Dan Streetman <ddstreet@ieee.org>]

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.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
---
 include/linux/zpool.h |  2 ++
 mm/zpool.c            | 25 +++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/zpool.h b/include/linux/zpool.h
index c924a28..42f8ec9 100644
--- a/include/linux/zpool.h
+++ b/include/linux/zpool.h
@@ -36,6 +36,8 @@ enum zpool_mapmode {
 	ZPOOL_MM_DEFAULT = ZPOOL_MM_RW
 };
 
+bool zpool_has_pool(char *type);
+
 struct zpool *zpool_create_pool(char *type, char *name,
 			gfp_t gfp, const struct zpool_ops *ops);
 
diff --git a/mm/zpool.c b/mm/zpool.c
index 951db32..aafcf8f 100644
--- a/mm/zpool.c
+++ b/mm/zpool.c
@@ -100,6 +100,31 @@ static void zpool_put_driver(struct zpool_driver *driver)
 }
 
 /**
+ * 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;
+}
+EXPORT_SYMBOL(zpool_has_pool);
+
+/**
  * zpool_create_pool() - Create a new zpool
  * @type	The type of the zpool to create (e.g. zbud, zsmalloc)
  * @name	The name of the zpool (e.g. zram0, zswap)
-- 
2.1.0

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