cryptoloop: add a deprecation warning

Support for cryptoloop has been officially marked broken and deprecated
in favor of dm-crypt (which supports the same broken algorithms if
needed) in Linux 2.6.4 (released in March 2004), and support for it has
been entirely removed from losetup in util-linux 2.23 (released in April
2013).  Add a warning and a deprecation schedule.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210827163250.255325-1-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/Kconfig

@@ -213,7 +213,7 @@ config BLK_DEV_LOOP_MIN_COUNT
 	  dynamically allocated with the /dev/loop-control interface.
 
 config BLK_DEV_CRYPTOLOOP
-	tristate "Cryptoloop Support"
+	tristate "Cryptoloop Support (DEPRECATED)"
 	select CRYPTO
 	select CRYPTO_CBC
 	depends on BLK_DEV_LOOP
@@ -225,7 +225,7 @@ config BLK_DEV_CRYPTOLOOP
 	  WARNING: This device is not safe for journaled file systems like
 	  ext3 or Reiserfs. Please use the Device Mapper crypto module
 	  instead, which can be configured to be on-disk compatible with the
-	  cryptoloop device.
+	  cryptoloop device.  cryptoloop support will be removed in Linux 5.16.
 
 source "drivers/block/drbd/Kconfig"
 

drivers/block/cryptoloop.c

@@ -189,6 +189,8 @@ init_cryptoloop(void)
 
 	if (rc)
 		printk(KERN_ERR "cryptoloop: loop_register_transfer failed\n");
+	else
+		pr_warn("the cryptoloop driver has been deprecated and will be removed in in Linux 5.16\n");
 	return rc;
 }