Date:   Thu, 10 Oct 2019 15:56:39 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        John Linville <linville@...driver.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Johannes Berg <johannes@...solutions.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v7 09/17] ethtool: generic handlers for GET
 requests

Wed, Oct 09, 2019 at 10:59:27PM CEST, mkubecek@...e.cz wrote:
>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
>standard handlers ethnl_get_doit(), ethnl_get_dumpit(), ethnl_get_start()
>and ethnl_get_done() can be then used in genl_ops handler. Notification
>handler will be introduced in a later patch.
>
>Signed-off-by: Michal Kubecek <mkubecek@...e.cz>
>---
> net/ethtool/netlink.c | 329 ++++++++++++++++++++++++++++++++++++++++++
> net/ethtool/netlink.h | 120 ++++++++++++++-
> 2 files changed, 448 insertions(+), 1 deletion(-)
>
>diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
>index ed9c0f82aca4..e5aade3b69d1 100644
>--- a/net/ethtool/netlink.c
>+++ b/net/ethtool/netlink.c
>@@ -177,6 +177,335 @@ struct sk_buff *ethnl_reply_init(size_t payload, struct net_device *dev, u8 cmd,
> 	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_get_start() and used in
>+ * ethnl_get_dumpit() and ethnl_get_done().
>+ */
>+struct ethnl_dump_ctx {
>+	const struct get_request_ops	*ops;
>+	struct ethnl_req_info		*req_info;
>+	struct ethnl_reply_data		*reply_data;
>+	int				pos_hash;
>+	int				pos_idx;
>+};
>+
>+static const struct get_request_ops *get_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_std_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_std_parse(struct ethnl_req_info *req_info,

"std" sounds a bit odd. Perhaps "common"?


>+			   const struct nlmsghdr *nlhdr, struct net *net,
>+			   const struct get_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, request_ops->header_policy,
>+				 require_dev);

This is odd. It's the other way around in compare what I would expect.
There is a request-specific header attr that contains common header
attributes parsed in ethnl_parse_header.

Why don't you have the common header as a root then then have one nested
attr that would carry the request-specific attrs?

Similar to how it is done in rtnl IFLA_INFO_KIND.

You can parse the common stuff in pre_doit/start genl ops and you
don't have to explicitly call ethnl_parse_header.
Also, that would allow you to benefit from the genl doit/dumpit initial
attr parsing and save basically this whole function (alloc,parse).

Code would be much more simple to follow then.

Still seems to me that you use the generic netlink but you don't like
the infra too much so you make it up yourself again in parallel - that is
my feeling reading the code. I get the argument about the similarities
of the individual requests and why you have this request_ops (alhough I
don't like it too much).


>+	if (ret < 0)
>+		goto out;
>+
>+	if (request_ops->parse_request) {
>+		ret = request_ops->parse_request(req_info, tb, extack);
>+		if (ret < 0)
>+			goto out;
>+	}
>+
>+	if (req_info->req_flags & ~request_ops->all_reqflags) {
>+		ret = -EOPNOTSUPP;
>+		NL_SET_ERR_MSG_ATTR(extack, tb[ETHTOOL_A_HEADER_RFLAGS],
>+				    "unsupported request specific flags");
>+		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 get_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 get_request_ops *ops,
>+				  struct net_device *dev)
>+{
>+	memset(reply_data, '\0', ops->reply_data_size);

Just "0" would do too.


>+	reply_data->dev = dev;
>+}
>+
>+/* generic ->doit() handler for GET type requests */
>+static int ethnl_get_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 get_request_ops *ops;
>+	struct sk_buff *rskb;
>+	void *reply_payload;
>+	int reply_len;
>+	int ret;
>+
>+	ops = get_requests[cmd];
>+	if (WARN_ONCE(!ops, "cmd %u has no get_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_std_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,

No need to wrap here (and in other similar cases)


>+		  "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_get_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;
>+}
>+
>+/* Generic ->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_get_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_get_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_get_start(struct netlink_callback *cb)
>+{
>+	struct ethnl_dump_ctx *ctx = ethnl_dump_context(cb);
>+	struct ethnl_reply_data *reply_data;
>+	const struct get_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 = get_requests[ghdr->cmd];
>+	if (WARN_ONCE(!ops, "cmd %u has no get_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_std_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;
>+}
>+
>+/* generic ->done() handler for GET requests */
>+static int ethnl_get_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,
>diff --git a/net/ethtool/netlink.h b/net/ethtool/netlink.h
>index 4c0b5ca439f8..077966a33544 100644
>--- a/net/ethtool/netlink.h
>+++ b/net/ethtool/netlink.h
>@@ -210,13 +210,30 @@ static inline unsigned int ethnl_reply_header_size(void)
> 			      nla_total_size(IFNAMSIZ));
> }
> 
>+/* GET request handling */
>+
>+/* Unified processing of GET requests uses two data structures: request info
>+ * and reply data. Request info holds information parsed from client request
>+ * and its stays constant through all request processing. Reply data holds data
>+ * retrieved from ethtool_ops callbacks or other internal sources which is used
>+ * to compose the reply. When processing a dump request, request info is filled
>+ * only once (when the request message is parsed) but reply data is filled for
>+ * each reply message.
>+ *
>+ * Both structures consist of part common for all request types (struct
>+ * ethnl_req_info and struct ethnl_reply_data defined below) and optional
>+ * parts specific for each request type. Common part always starts at offset 0.
>+ */
>+
> /**
>  * struct ethnl_req_info - base type of request information for GET requests
>  * @dev:          network device the request is for (may be null)
>  * @global_flags: request flags common for all request types
>  * @req_flags:    request flags specific for each request type
>  *
>- * This is a common base, additional members may follow after this structure.
>+ * This is a common base for request specific structures holding data from
>+ * parsed userspace request. These always embed struct ethnl_req_info at
>+ * zero offset.
>  */
> struct ethnl_req_info {
> 	struct net_device		*dev;
>@@ -224,4 +241,105 @@ struct ethnl_req_info {
> 	u32				req_flags;
> };
> 
>+/**
>+ * struct ethnl_reply_data - base type of reply data for GET requests
>+ * @dev:       device for current reply message; in single shot requests it is
>+ *             equal to &ethnl_req_info.dev; in dumps it's different for each
>+ *             reply message
>+ *
>+ * This is a common base for request specific structures holding data for
>+ * kernel reply message. These always embed struct ethnl_reply_data at zero
>+ * offset.
>+ */
>+struct ethnl_reply_data {
>+	struct net_device		*dev;
>+};
>+
>+static inline int ethnl_before_ops(struct net_device *dev)
>+{
>+	if (dev && dev->ethtool_ops->begin)
>+		return dev->ethtool_ops->begin(dev);
>+	else
>+		return 0;
>+}
>+
>+static inline void ethnl_after_ops(struct net_device *dev)
>+{
>+	if (dev && dev->ethtool_ops->complete)
>+		dev->ethtool_ops->complete(dev);
>+}
>+
>+/**
>+ * struct get_request_ops - unified handling of GET requests
>+ * @request_cmd:      command id for request (GET)
>+ * @reply_cmd:        command id for reply (GET_REPLY)
>+ * @hdr_attr:         attribute type for request header
>+ * @max_attr:         maximum (top level) attribute type
>+ * @req_info_size:    size of request info
>+ * @reply_data_size:  size of reply data
>+ * @request_policy:   netlink policy for message contents
>+ * @header_policy:    (optional) netlink policy for request header
>+ * @all_reqflags:     allowed request specific flags
>+ * @allow_nodev_do:   allow non-dump request with no device identification
>+ * @parse_request:
>+ *	Parse request except common header (struct ethnl_req_info). Common
>+ *	header is already filled on entry, the rest up to @repdata_offset
>+ *	is zero initialized. This callback should only modify type specific
>+ *	request info by parsed attributes from request message.
>+ * @prepare_data:
>+ *	Retrieve and prepare data needed to compose a reply message. Calls to
>+ *	ethtool_ops handlers should be limited to this callback. Common reply
>+ *	data (struct ethnl_reply_data) is filled on entry, type specific part
>+ *	after it is zero initialized. This callback should only modify the
>+ *	type specific part of reply data. Device identification from struct
>+ *	ethnl_reply_data is to be used as for dump requests, it iterates
>+ *	through network devices which common_req_info::dev points to the

First time I see this notation. Is "::" something common in kernel code?


>+ *	device from client request.
>+ * @reply_size:
>+ *	Estimate reply message size. Returned value must be sufficient for
>+ *	message payload without common reply header. The callback may returned
>+ *	estimate higher than actual message size if exact calculation would
>+ *	not be worth the saved memory space.
>+ * @fill_reply:
>+ *	Fill reply message payload (except for common header) from reply data.
>+ *	The callback must not generate more payload than previously called
>+ *	->reply_size() estimated.
>+ * @cleanup_data:
>+ *	Optional cleanup called when reply data is no longer needed. Can be
>+ *	used e.g. to free any additional data structures outside the main
>+ *	structure which were allocated by ->prepare_data(). When processing
>+ *	dump requests, ->cleanup() is called for each message.
>+ *
>+ * Description of variable parts of GET request handling when using the unified
>+ * infrastructure. When used, a pointer to an instance of this structure is to
>+ * be added to &get_requests array and generic handlers ethnl_get_doit(),
>+ * ethnl_get_dumpit(), ethnl_get_start() and ethnl_get_done() used in
>+ * @ethnl_genl_ops
>+ */
>+struct get_request_ops {

Could you please have "ethnl_" prefix for things like this.
"get_request_ops" sounds way to generic.


>+	u8			request_cmd;
>+	u8			reply_cmd;
>+	u16			hdr_attr;
>+	unsigned int		max_attr;
>+	unsigned int		req_info_size;
>+	unsigned int		reply_data_size;
>+	const struct nla_policy *request_policy;
>+	const struct nla_policy *header_policy;
>+	u32			all_reqflags;
>+	bool			allow_nodev_do;
>+
>+	int (*parse_request)(struct ethnl_req_info *req_info,
>+			     struct nlattr **tb,
>+			     struct netlink_ext_ack *extack);
>+	int (*prepare_data)(const struct ethnl_req_info *req_info,
>+			    struct ethnl_reply_data *reply_data,
>+			    struct genl_info *info);
>+	int (*reply_size)(const struct ethnl_req_info *req_info,
>+			  const struct ethnl_reply_data *reply_data);
>+	int (*fill_reply)(struct sk_buff *skb,
>+			  const struct ethnl_req_info *req_info,
>+			  const struct ethnl_reply_data *reply_data);
>+	void (*cleanup_data)(struct ethnl_reply_data *reply_data);
>+};
>+
> #endif /* _NET_ETHTOOL_NETLINK_H */
>-- 
>2.23.0
>

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