block/keyslot-manager: introduce devm_blk_ksm_init()

Add a resource-managed variant of blk_ksm_init() so that drivers don't
have to worry about calling blk_ksm_destroy().

Note that the implementation uses a custom devres action to call
blk_ksm_destroy() rather than switching the two allocations to be
directly devres-managed, e.g. with devm_kmalloc().  This is because we
need to keep zeroing the memory containing the keyslots when it is
freed, and also because we want to continue using kvmalloc() (and there
is no devm_kvmalloc()).

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Satya Tangirala <satyat@google.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20210121082155.111333-2-ebiggers@kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

block/keyslot-manager.c

@@ -29,6 +29,7 @@
 #define pr_fmt(fmt) "blk-crypto: " fmt
 
 #include <linux/keyslot-manager.h>
+#include <linux/device.h>
 #include <linux/atomic.h>
 #include <linux/mutex.h>
 #include <linux/pm_runtime.h>
@@ -127,6 +128,34 @@ err_destroy_ksm:
 }
 EXPORT_SYMBOL_GPL(blk_ksm_init);
 
+static void blk_ksm_destroy_callback(void *ksm)
+{
+	blk_ksm_destroy(ksm);
+}
+
+/**
+ * devm_blk_ksm_init() - Resource-managed blk_ksm_init()
+ * @dev: The device which owns the blk_keyslot_manager.
+ * @ksm: The blk_keyslot_manager to initialize.
+ * @num_slots: The number of key slots to manage.
+ *
+ * Like blk_ksm_init(), but causes blk_ksm_destroy() to be called automatically
+ * on driver detach.
+ *
+ * Return: 0 on success, or else a negative error code.
+ */
+int devm_blk_ksm_init(struct device *dev, struct blk_keyslot_manager *ksm,
+		      unsigned int num_slots)
+{
+	int err = blk_ksm_init(ksm, num_slots);
+
+	if (err)
+		return err;
+
+	return devm_add_action_or_reset(dev, blk_ksm_destroy_callback, ksm);
+}
+EXPORT_SYMBOL_GPL(devm_blk_ksm_init);
+
 static inline struct hlist_head *
 blk_ksm_hash_bucket_for_key(struct blk_keyslot_manager *ksm,
 			    const struct blk_crypto_key *key)