nvme: expose TLS mode

It is not possible to determine the active TLS mode from the
presence or absence of sysfs attributes like tls_key,
tls_configured_key, or dhchap_secret.

With the introduction of the concat mode and optional DH-CHAP
authentication, different configurations can result in identical
sysfs state. This makes user space detection unreliable.

Expose the TLS mode explicitly to allow user space to
unambiguously identify the active configuration and avoid
fragile heuristics in nvme-cli.

Reviewed-by: Chris Leech <cleech@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Daniel Wagner <wagi@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>

Author: igaw

drivers/nvme/host/sysfs.c

@@ -883,10 +883,26 @@ static ssize_t tls_keyring_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(tls_keyring);
 
+static ssize_t tls_mode_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct nvme_ctrl *ctrl = dev_get_drvdata(dev);
+	const char *mode;
+
+	if (ctrl->opts->tls)
+		mode = "tls";
+	else
+		mode = "concat";
+
+	return sysfs_emit(buf, "%s\n", mode);
+}
+static DEVICE_ATTR_RO(tls_mode);
+
 static struct attribute *nvme_tls_attrs[] = {
 	&dev_attr_tls_key.attr,
 	&dev_attr_tls_configured_key.attr,
 	&dev_attr_tls_keyring.attr,
+	&dev_attr_tls_mode.attr,
 	NULL,
 };
 
@@ -908,6 +924,9 @@ static umode_t nvme_tls_attrs_are_visible(struct kobject *kobj,
 	if (a == &dev_attr_tls_keyring.attr &&
 	    !ctrl->opts->keyring)
 		return 0;
+	if (a == &dev_attr_tls_mode.attr &&
+	    !ctrl->opts->tls && !ctrl->opts->concat)
+		return 0;
 
 	return a->mode;
 }