nvme: common: make keyring and auth separate modules

When only the keyring module is included but auth is not, modpost
complains about the lack of a module license tag:

ERROR: modpost: missing MODULE_LICENSE() in drivers/nvme/common/nvme-common.o

Address this by making both modules buildable standalone,
removing the now unnecessary CONFIG_NVME_COMMON symbol
in the process.

Also, now that NVME_KEYRING config symbol can be either a module or
built-in, the stubs need to check for '#if IS_ENABLED' rather than a
simple '#ifdef'.

Fixes: 9d77eb5277849 ("nvme-keyring: register '.nvme' keyring")
Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Hannes Reinecke <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Keith Busch <[e-mail]>

drivers/nvme/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
 
-obj-$(CONFIG_NVME_COMMON)		+= common/
+obj-y		+= common/
 obj-y		+= host/
 obj-y		+= target/

drivers/nvme/common/Kconfig

···
 # SPDX-License-Identifier: GPL-2.0-only
 
-config NVME_COMMON
-       tristate
-
 config NVME_KEYRING
-       bool
+       tristate
        select KEYS
 
 config NVME_AUTH
-	bool
+	tristate
 	select CRYPTO
 	select CRYPTO_HMAC
 	select CRYPTO_SHA256

drivers/nvme/common/Makefile

···
 
 ccflags-y			+= -I$(src)
 
-obj-$(CONFIG_NVME_COMMON)	+= nvme-common.o
+obj-$(CONFIG_NVME_AUTH)		+= nvme-auth.o
+obj-$(CONFIG_NVME_KEYRING)	+= nvme-keyring.o
 
-nvme-common-$(CONFIG_NVME_AUTH)	+= auth.o
-nvme-common-$(CONFIG_NVME_KEYRING) += keyring.o
+nvme-auth-y			+= auth.o
+nvme-keyring-y			+= keyring.o

drivers/nvme/common/keyring.c

···
 	key_put(nvme_keyring);
 }
 EXPORT_SYMBOL_GPL(nvme_keyring_exit);
+
+MODULE_LICENSE("GPL v2");

drivers/nvme/host/Kconfig

···
 config NVME_TCP_TLS
 	bool "NVMe over Fabrics TCP TLS encryption support"
 	depends on NVME_TCP
-	select NVME_COMMON
 	select NVME_KEYRING
 	select NET_HANDSHAKE
 	select KEYS
···
 config NVME_HOST_AUTH
 	bool "NVM Express over Fabrics In-Band Authentication"
 	depends on NVME_CORE
-	select NVME_COMMON
 	select NVME_AUTH
 	help
 	  This provides support for NVMe over Fabrics In-Band Authentication.

drivers/nvme/target/Kconfig

···
 config NVME_TARGET_TCP_TLS
 	bool "NVMe over Fabrics TCP target TLS encryption support"
 	depends on NVME_TARGET_TCP
-	select NVME_COMMON
 	select NVME_KEYRING
 	select NET_HANDSHAKE
 	select KEYS
···
 config NVME_TARGET_AUTH
 	bool "NVMe over Fabrics In-band Authentication support"
 	depends on NVME_TARGET
-	select NVME_COMMON
 	select NVME_AUTH
 	help
 	  This enables support for NVMe over Fabrics In-band Authentication

include/linux/nvme-keyring.h

···
 #ifndef _NVME_KEYRING_H
 #define _NVME_KEYRING_H
 
-#ifdef CONFIG_NVME_KEYRING
+#if IS_ENABLED(CONFIG_NVME_KEYRING)
 
 key_serial_t nvme_tls_psk_default(struct key *keyring,
 		const char *hostnqn, const char *subnqn);