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

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>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
index 282d54117e0ac710f7aed294b54ea49dd746b414..7ae041e2b3fb0508f0016e6473e8a5e040902139 100644 (file)
--- a/drivers/nvme/host/fabrics.c
+++ b/drivers/nvme/host/fabrics.c
@@ -1069,6 +1069,26 @@ out_unlock:
        return ret ? ret : count;
 }
 
+static void __nvmf_concat_opt_tokens(struct seq_file *seq_file)
+{
+       const struct match_token *tok;
+       int idx;
+
+       /*
+        * Add dummy entries for instance and cntlid to
+        * signal an invalid/non-existing controller
+        */
+       seq_puts(seq_file, "instance=-1,cntlid=-1");
+       for (idx = 0; idx < ARRAY_SIZE(opt_tokens); idx++) {
+               tok = &opt_tokens[idx];
+               if (tok->token == NVMF_OPT_ERR)
+                       continue;
+               seq_puts(seq_file, ",");
+               seq_puts(seq_file, tok->pattern);
+       }
+       seq_puts(seq_file, "\n");
+}
+
 static int nvmf_dev_show(struct seq_file *seq_file, void *private)
 {
        struct nvme_ctrl *ctrl;
@@ -1077,7 +1097,7 @@ 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;
+               __nvmf_concat_opt_tokens(seq_file);
                goto out_unlock;
        }