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 <arnd@arndb.de>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

nvme-keyring: register '.nvme' keyring

Register a '.nvme' keyring to hold keys for TLS and DH-HMAC-CHAP and
add a new config option NVME_KEYRING.
We need a separate keyring for NVMe as the configuration is done
via individual commands (eg for configfs), and the usual per-session
or per-process keyrings can't be used.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>

nvme: implement In-Band authentication

Implement NVMe-oF In-Band authentication according to NVMe TPAR 8006.
This patch adds two new fabric options 'dhchap_secret' to specify the
pre-shared key (in ASCII respresentation according to NVMe 2.0 section
8.13.5.8 'Secret representation') and 'dhchap_ctrl_secret' to specify
the pre-shared controller key for bi-directional authentication of both
the host and the controller.
Re-authentication can be triggered by writing the PSK into the new
controller sysfs attribute 'dhchap_secret' or 'dhchap_ctrl_secret'.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
[axboe: fold in clang build fix]
Signed-off-by: Jens Axboe <axboe@kernel.dk>