ethtool: default handlers for GET requests

Significant part of GET request processing is common for most request
types but unfortunately it cannot be easily separated from type specific
code as we need to alternate between common actions (parsing common request
header, allocating message and filling netlink/genetlink headers etc.) and
specific actions (querying the device, composing the reply). The processing
also happens in three different situations: "do" request, "dump" request
and notification, each doing things in slightly different way.

The request specific code is implemented in four or five callbacks defined
in an instance of struct get_request_ops:

  parse_request() - parse incoming message
  prepare_data()  - retrieve data from driver or NIC
  reply_size()    - estimate reply message size
  fill_reply()    - compose reply message
  cleanup_data()  - (optional) clean up additional data

Other members of struct get_request_ops describe the data structure holding
information from client request and data used to compose the message. The
default handlers ethnl_default_doit(), ethnl_default_dumpit(),
ethnl_default_start() and ethnl_default_done() can be then used in genl_ops
handler. Notification handler will be introduced in a later patch.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 321 insertions, 0 deletions

diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index c0f25c8f3565..ae63e8423072 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -171,6 +171,327 @@ err:
 	return NULL;
 }
 
+/* GET request helpers */
+
+/**
+ * struct ethnl_dump_ctx - context structure for generic dumpit() callback
+ * @ops:      request ops of currently processed message type
+ * @req_info: parsed request header of processed request
+ * @pos_hash: saved iteration position - hashbucket
+ * @pos_idx:  saved iteration position - index
+ *
+ * These parameters are kept in struct netlink_callback as context preserved
+ * between iterations. They are initialized by ethnl_default_start() and used
+ * in ethnl_default_dumpit() and ethnl_default_done().
+ */
+struct ethnl_dump_ctx {
+	const struct ethnl_request_ops	*ops;
+	struct ethnl_req_info		*req_info;
+	struct ethnl_reply_data		*reply_data;
+	int				pos_hash;
+	int				pos_idx;
+};
+
+static const struct ethnl_request_ops *
+ethnl_default_requests[__ETHTOOL_MSG_USER_CNT] = {
+};
+
+static struct ethnl_dump_ctx *ethnl_dump_context(struct netlink_callback *cb)
+{
+	return (struct ethnl_dump_ctx *)cb->ctx;
+}
+
+/**
+ * ethnl_default_parse() - Parse request message
+ * @req_info:    pointer to structure to put data into
+ * @nlhdr:       pointer to request message header
+ * @net:         request netns
+ * @request_ops: struct request_ops for request type
+ * @extack:      netlink extack for error reporting
+ * @require_dev: fail if no device identified in header
+ *
+ * Parse universal request header and call request specific ->parse_request()
+ * callback (if defined) to parse the rest of the message.
+ *
+ * Return: 0 on success or negative error code
+ */
+static int ethnl_default_parse(struct ethnl_req_info *req_info,
+			       const struct nlmsghdr *nlhdr, struct net *net,
+			       const struct ethnl_request_ops *request_ops,
+			       struct netlink_ext_ack *extack, bool require_dev)
+{
+	struct nlattr **tb;
+	int ret;
+
+	tb = kmalloc_array(request_ops->max_attr + 1, sizeof(tb[0]),
+			   GFP_KERNEL);
+	if (!tb)
+		return -ENOMEM;
+
+	ret = nlmsg_parse(nlhdr, GENL_HDRLEN, tb, request_ops->max_attr,
+			  request_ops->request_policy, extack);
+	if (ret < 0)
+		goto out;
+	ret = ethnl_parse_header(req_info, tb[request_ops->hdr_attr], net,
+				 extack, require_dev);
+	if (ret < 0)
+		goto out;
+
+	if (request_ops->parse_request) {
+		ret = request_ops->parse_request(req_info, tb, extack);
+		if (ret < 0)
+			goto out;
+	}
+
+	ret = 0;
+out:
+	kfree(tb);
+	return ret;
+}
+
+/**
+ * ethnl_init_reply_data() - Initialize reply data for GET request
+ * @req_info: pointer to embedded struct ethnl_req_info
+ * @ops:      instance of struct ethnl_request_ops describing the layout
+ * @dev:      network device to initialize the reply for
+ *
+ * Fills the reply data part with zeros and sets the dev member. Must be called
+ * before calling the ->fill_reply() callback (for each iteration when handling
+ * dump requests).
+ */
+static void ethnl_init_reply_data(struct ethnl_reply_data *reply_data,
+				  const struct ethnl_request_ops *ops,
+				  struct net_device *dev)
+{
+	memset(reply_data, 0, ops->reply_data_size);
+	reply_data->dev = dev;
+}
+
+/* default ->doit() handler for GET type requests */
+static int ethnl_default_doit(struct sk_buff *skb, struct genl_info *info)
+{
+	struct ethnl_reply_data *reply_data = NULL;
+	struct ethnl_req_info *req_info = NULL;
+	const u8 cmd = info->genlhdr->cmd;
+	const struct ethnl_request_ops *ops;
+	struct sk_buff *rskb;
+	void *reply_payload;
+	int reply_len;
+	int ret;
+
+	ops = ethnl_default_requests[cmd];
+	if (WARN_ONCE(!ops, "cmd %u has no ethnl_request_ops\n", cmd))
+		return -EOPNOTSUPP;
+	req_info = kzalloc(ops->req_info_size, GFP_KERNEL);
+	if (!req_info)
+		return -ENOMEM;
+	reply_data = kmalloc(ops->reply_data_size, GFP_KERNEL);
+	if (!reply_data) {
+		kfree(req_info);
+		return -ENOMEM;
+	}
+
+	ret = ethnl_default_parse(req_info, info->nlhdr, genl_info_net(info), ops,
+				  info->extack, !ops->allow_nodev_do);
+	if (ret < 0)
+		goto err_dev;
+	ethnl_init_reply_data(reply_data, ops, req_info->dev);
+
+	rtnl_lock();
+	ret = ops->prepare_data(req_info, reply_data, info);
+	rtnl_unlock();
+	if (ret < 0)
+		goto err_cleanup;
+	reply_len = ops->reply_size(req_info, reply_data);
+	if (ret < 0)
+		goto err_cleanup;
+	ret = -ENOMEM;
+	rskb = ethnl_reply_init(reply_len, req_info->dev, ops->reply_cmd,
+				ops->hdr_attr, info, &reply_payload);
+	if (!rskb)
+		goto err_cleanup;
+	ret = ops->fill_reply(rskb, req_info, reply_data);
+	if (ret < 0)
+		goto err_msg;
+	if (ops->cleanup_data)
+		ops->cleanup_data(reply_data);
+
+	genlmsg_end(rskb, reply_payload);
+	if (req_info->dev)
+		dev_put(req_info->dev);
+	kfree(reply_data);
+	kfree(req_info);
+	return genlmsg_reply(rskb, info);
+
+err_msg:
+	WARN_ONCE(ret == -EMSGSIZE, "calculated message payload length (%d) not sufficient\n", reply_len);
+	nlmsg_free(rskb);
+err_cleanup:
+	if (ops->cleanup_data)
+		ops->cleanup_data(reply_data);
+err_dev:
+	if (req_info->dev)
+		dev_put(req_info->dev);
+	kfree(reply_data);
+	kfree(req_info);
+	return ret;
+}
+
+static int ethnl_default_dump_one(struct sk_buff *skb, struct net_device *dev,
+				  const struct ethnl_dump_ctx *ctx)
+{
+	int ret;
+
+	ethnl_init_reply_data(ctx->reply_data, ctx->ops, dev);
+	rtnl_lock();
+	ret = ctx->ops->prepare_data(ctx->req_info, ctx->reply_data, NULL);
+	rtnl_unlock();
+	if (ret < 0)
+		goto out;
+	ret = ethnl_fill_reply_header(skb, dev, ctx->ops->hdr_attr);
+	if (ret < 0)
+		goto out;
+	ret = ctx->ops->fill_reply(skb, ctx->req_info, ctx->reply_data);
+
+out:
+	if (ctx->ops->cleanup_data)
+		ctx->ops->cleanup_data(ctx->reply_data);
+	ctx->reply_data->dev = NULL;
+	return ret;
+}
+
+/* Default ->dumpit() handler for GET requests. Device iteration copied from
+ * rtnl_dump_ifinfo(); we have to be more careful about device hashtable
+ * persistence as we cannot guarantee to hold RTNL lock through the whole
+ * function as rtnetnlink does.
+ */
+static int ethnl_default_dumpit(struct sk_buff *skb,
+				struct netlink_callback *cb)
+{
+	struct ethnl_dump_ctx *ctx = ethnl_dump_context(cb);
+	struct net *net = sock_net(skb->sk);
+	int s_idx = ctx->pos_idx;
+	int h, idx = 0;
+	int ret = 0;
+	void *ehdr;
+
+	rtnl_lock();
+	for (h = ctx->pos_hash; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
+		struct hlist_head *head;
+		struct net_device *dev;
+		unsigned int seq;
+
+		head = &net->dev_index_head[h];
+
+restart_chain:
+		seq = net->dev_base_seq;
+		cb->seq = seq;
+		idx = 0;
+		hlist_for_each_entry(dev, head, index_hlist) {
+			if (idx < s_idx)
+				goto cont;
+			dev_hold(dev);
+			rtnl_unlock();
+
+			ehdr = genlmsg_put(skb, NETLINK_CB(cb->skb).portid,
+					   cb->nlh->nlmsg_seq,
+					   &ethtool_genl_family, 0,
+					   ctx->ops->reply_cmd);
+			if (!ehdr) {
+				dev_put(dev);
+				ret = -EMSGSIZE;
+				goto out;
+			}
+			ret = ethnl_default_dump_one(skb, dev, ctx);
+			dev_put(dev);
+			if (ret < 0) {
+				genlmsg_cancel(skb, ehdr);
+				if (ret == -EOPNOTSUPP)
+					goto lock_and_cont;
+				if (likely(skb->len))
+					ret = skb->len;
+				goto out;
+			}
+			genlmsg_end(skb, ehdr);
+lock_and_cont:
+			rtnl_lock();
+			if (net->dev_base_seq != seq) {
+				s_idx = idx + 1;
+				goto restart_chain;
+			}
+cont:
+			idx++;
+		}
+
+	}
+	rtnl_unlock();
+
+out:
+	ctx->pos_hash = h;
+	ctx->pos_idx = idx;
+	nl_dump_check_consistent(cb, nlmsg_hdr(skb));
+
+	return ret;
+}
+
+/* generic ->start() handler for GET requests */
+static int ethnl_default_start(struct netlink_callback *cb)
+{
+	struct ethnl_dump_ctx *ctx = ethnl_dump_context(cb);
+	struct ethnl_reply_data *reply_data;
+	const struct ethnl_request_ops *ops;
+	struct ethnl_req_info *req_info;
+	struct genlmsghdr *ghdr;
+	int ret;
+
+	BUILD_BUG_ON(sizeof(*ctx) > sizeof(cb->ctx));
+
+	ghdr = nlmsg_data(cb->nlh);
+	ops = ethnl_default_requests[ghdr->cmd];
+	if (WARN_ONCE(!ops, "cmd %u has no ethnl_request_ops\n", ghdr->cmd))
+		return -EOPNOTSUPP;
+	req_info = kzalloc(ops->req_info_size, GFP_KERNEL);
+	if (!req_info)
+		return -ENOMEM;
+	reply_data = kmalloc(ops->reply_data_size, GFP_KERNEL);
+	if (!reply_data) {
+		kfree(req_info);
+		return -ENOMEM;
+	}
+
+	ret = ethnl_default_parse(req_info, cb->nlh, sock_net(cb->skb->sk), ops,
+				  cb->extack, false);
+	if (req_info->dev) {
+		/* We ignore device specification in dump requests but as the
+		 * same parser as for non-dump (doit) requests is used, it
+		 * would take reference to the device if it finds one
+		 */
+		dev_put(req_info->dev);
+		req_info->dev = NULL;
+	}
+	if (ret < 0)
+		return ret;
+
+	ctx->ops = ops;
+	ctx->req_info = req_info;
+	ctx->reply_data = reply_data;
+	ctx->pos_hash = 0;
+	ctx->pos_idx = 0;
+
+	return 0;
+}
+
+/* default ->done() handler for GET requests */
+static int ethnl_default_done(struct netlink_callback *cb)
+{
+	struct ethnl_dump_ctx *ctx = ethnl_dump_context(cb);
+
+	kfree(ctx->reply_data);
+	kfree(ctx->req_info);
+
+	return 0;
+}
+
 /* notifications */
 
 typedef void (*ethnl_notify_handler_t)(struct net_device *dev, unsigned int cmd,