[PATCH] nvme: print out valid arguments when reading from /dev/nvme-fabrics

[Hannes Reinecke <hare@suse.de>]

Currently applications have a hard time figuring out which
nvme-over-fabrics arguments are supported for any given kernel;
the ioctl will return an error code on failure, and the application
has to guess whether this was due to an invalid argument or due
to a connection or controller error.
With this patch applications can read a list of supported
arguments by simply reading from /dev/nvme-fabrics, allowing
them to validate the connection string.

Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 drivers/nvme/host/fabrics.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
index 0ac054f80a82..810bbc8c9b6b 100644
--- a/drivers/nvme/host/fabrics.c
+++ b/drivers/nvme/host/fabrics.c
@@ -1144,7 +1144,18 @@ static int nvmf_dev_show(struct seq_file *seq_file, void *private)
 	mutex_lock(&nvmf_dev_mutex);
 	ctrl = seq_file->private;
 	if (!ctrl) {
-		ret = -EINVAL;
+		const struct match_token *tok;
+		int idx;
+
+		for (idx = 0; idx < ARRAY_SIZE(opt_tokens); idx++) {
+			tok = &opt_tokens[idx];
+			if (tok->token == NVMF_OPT_ERR)
+				continue;
+			if (idx)
+				seq_puts(seq_file, ",");
+			seq_puts(seq_file, tok->pattern);
+		}
+		seq_puts(seq_file, "\n");
 		goto out_unlock;
 	}
 
-- 
2.29.2