[PATCH v1 8/8] sunrpc: introduce an 'add' node to 'multipath' sysfs directory

[Dan Aloni <dan@xxxxxxxxxxxx>]

This allows adding new transports to an existing multipath switch. This
is similar to what the `nconnect` mount parameter does, but instead we
can do this while the NFS mount is live.

For example:

    echo 'dstaddr 192.168.40.8 kind rdma' \
	   > /sys/kernel/sunrpc/client/0/multipath/add

Signed-off-by: Dan Aloni <dan@xxxxxxxxxxxx>
---
 net/sunrpc/sysfs.c | 104 +++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 101 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/sysfs.c b/net/sunrpc/sysfs.c
index 3592f3b862b2..d745dfb7cef4 100644
--- a/net/sunrpc/sysfs.c
+++ b/net/sunrpc/sysfs.c
@@ -315,18 +315,116 @@ static ssize_t rpc_netns_multipath_list_show(struct kobject *kobj,
 	return pos;
 }
 
-static ssize_t rpc_netns_multipath_list_store(struct kobject *kobj,
+static ssize_t rpc_netns_multipath_add_store(struct kobject *kobj,
 		struct kobj_attribute *attr, const char *buf, size_t count)
 {
-	return -EINVAL;
+	struct rpc_netns_multipath *c =
+		container_of(kobj, struct rpc_netns_multipath, kobject);
+	struct rpc_xprt_switch *xps = c->xps;
+	struct rpc_xprt_iter xpi;
+	struct sockaddr_storage addr;
+	struct xprt_create xprt_args = {
+		.ident = XPRT_TRANSPORT_RDMA,
+		.net = c->net,
+		.dstaddr = (struct sockaddr *)&addr,
+	};
+	struct rpc_xprt *existing_xprt;
+	char *opt, *str, *arg;
+	bool has_dstaddr = false;
+	bool has_kind = false;
+	int err;
+
+	opt = kstrndup(buf, count, GFP_KERNEL);
+	if (!opt)
+		return -ENOMEM;
+
+	str = strstrip(opt);
+
+	while (1) {
+		arg = strsep(&str, " ");
+		if (!arg)
+			break;
+
+		if (sysfs_streq(arg, "kind")) {
+			arg = strsep(&str, " ");
+			if (!arg) {
+				err = -EINVAL;
+				goto out;
+			}
+			if (has_kind) {
+				err = -EINVAL;
+				goto out;
+			}
+
+			if (sysfs_streq(arg, "rdma")) {
+				xprt_args.ident = XPRT_TRANSPORT_RDMA;
+			} else if (sysfs_streq(arg, "tcp")) {
+				xprt_args.ident = XPRT_TRANSPORT_TCP;
+			} else {
+				err = -EINVAL;
+				goto out;
+			}
+
+			has_kind = true;
+		} else if (sysfs_streq(arg, "dstaddr")) {
+			arg = strsep(&str, " ");
+			if (!arg) {
+				err = -EINVAL;
+				goto out;
+			}
+			xprt_args.addrlen = rpc_pton(c->net,
+				arg, strlen(arg), (struct sockaddr *)&addr,
+				sizeof(addr));
+			if (has_dstaddr || !xprt_args.addrlen) {
+				err = -EINVAL;
+				goto out;
+			}
+
+			has_dstaddr = true;
+		} else {
+			break;
+		}
+	}
+
+	if (!has_dstaddr || !has_kind)  {
+		err = -EINVAL;
+		goto out;
+	}
+
+
+	/* Discover an existing xprt */
+	xprt_iter_init_listall(&xpi, xps);
+	existing_xprt = xprt_iter_get_next(&xpi);
+	xprt_iter_destroy(&xpi);
+
+	if (!existing_xprt) {
+		err = -ENOENT;
+		goto out;
+	}
+
+	xprt_args.servername = existing_xprt->servername;
+	xprt_iter_init_listall(&xpi, xps);
+	rpc_add_xprt(&xpi, NULL, &xprt_args, NULL, NULL);
+	xprt_iter_destroy(&xpi);
+
+	xprt_put(existing_xprt);
+
+	err = count;
+out:
+	kfree(opt);
+
+	return err;
 }
 
 static struct kobj_attribute rpc_netns_multipath_list = __ATTR(list,
-	0644, rpc_netns_multipath_list_show, rpc_netns_multipath_list_store);
+	0444, rpc_netns_multipath_list_show, NULL);
 
+static struct kobj_attribute rpc_netns_multipath_add = __ATTR(add,
+	0200, NULL, rpc_netns_multipath_add_store);
 
 static struct attribute *rpc_netns_multipath_attrs[] = {
 	&rpc_netns_multipath_list.attr,
+	&rpc_netns_multipath_add.attr,
 	NULL,
 };
 
-- 
2.26.2