nvme-tcp: print actual source IP address through sysfs "address" attr

TCP transport relies on the routing table to determine which source
address and interface to use when making a connection. Currently, there
is no way to tell from userspace where a connection was made. This
patch exposes the actual source address using a new field named
"src_addr=" in the "address" attribute.

This is needed to diagnose and identify connectivity issues. With the
source address we can infer the interface associated with each
connection.

This was tested with nvme-cli 2.0 to verify it does not have any
adverse effect. The new "src_addr=" field will simply be displayed in
the output of the "list-subsys" or "list -v" commands as shown here.

$ nvme list-subsys
nvme-subsys0 - NQN=nqn.2014-08.org.nvmexpress.discovery
\
 +- nvme0 tcp traddr=192.168.56.1,trsvcid=8009,src_addr=192.168.56.101 live
Signed-off-by: Martin Belanger <martin.belanger@dell.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/tcp.c

@@ -2546,6 +2546,25 @@ static int nvme_tcp_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
 	return queue->nr_cqe;
 }
 
+static int nvme_tcp_get_address(struct nvme_ctrl *ctrl, char *buf, int size)
+{
+	struct nvme_tcp_queue *queue = &to_tcp_ctrl(ctrl)->queues[0];
+	struct sockaddr_storage src_addr;
+	int ret, len;
+
+	len = nvmf_get_address(ctrl, buf, size);
+
+	ret = kernel_getsockname(queue->sock, (struct sockaddr *)&src_addr);
+	if (ret > 0) {
+		if (len > 0)
+			len--; /* strip trailing newline */
+		len += scnprintf(buf + len, size - len, "%ssrc_addr=%pISc\n",
+				(len) ? "," : "", &src_addr);
+	}
+
+	return len;
+}
+
 static const struct blk_mq_ops nvme_tcp_mq_ops = {
 	.queue_rq	= nvme_tcp_queue_rq,
 	.commit_rqs	= nvme_tcp_commit_rqs,
@@ -2577,7 +2596,7 @@ static const struct nvme_ctrl_ops nvme_tcp_ctrl_ops = {
 	.free_ctrl		= nvme_tcp_free_ctrl,
 	.submit_async_event	= nvme_tcp_submit_async_event,
 	.delete_ctrl		= nvme_tcp_delete_ctrl,
-	.get_address		= nvmf_get_address,
+	.get_address		= nvme_tcp_get_address,
 	.stop_ctrl		= nvme_tcp_stop_ctrl,
 };