[PATCHv2] nvme: print out valid arguments when reading from /dev/nvme-fabrics

[Chaitanya Kulkarni]

On 12/7/21 5:55 AM, Hannes Reinecke wrote:
> 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 at suse.de>
> ---
>   drivers/nvme/host/fabrics.c | 22 +++++++++++++++++++++-
>   1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
> index 282d54117e0a..7ae041e2b3fb 100644
> --- a/drivers/nvme/host/fabrics.c
> +++ b/drivers/nvme/host/fabrics.c
> @@ -1069,6 +1069,26 @@ static ssize_t nvmf_dev_write(struct file *file, const char __user *ubuf,
>   	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, ",");

Can we use "\n" instead of "," ?
with that change it looks :-

instance=-1,cntlid=-1
transport=%s
traddr=%s
trsvcid=%s
nqn=%s
queue_size=%d
nr_io_queues=%d
reconnect_delay=%d
ctrl_loss_tmo=%d
keep_alive_tmo=%d
hostnqn=%s
host_traddr=%s
host_iface=%s
hostid=%s
duplicate_connect
disable_sqflow
hdr_digest
data_digest
nr_write_queues=%d
nr_poll_queues=%d
tos=%d
fast_io_fail_tmo=%d
discovery