[Devel] [PATCH RHEL7 COMMIT] ms/netlink: add a start callback for starting a netlink dump

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.6.1.vz7.171.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.6.1.vz7.171.1
------>
commit f964b62f569410a6ed2de2ff8e6c5ba8f160749c
Author: Tom Herbert <tom at herbertland.com>
Date:   Thu Dec 3 12:21:24 2020 +0300

    ms/netlink: add a start callback for starting a netlink dump
    
    The start callback allows the caller to set up a context for the
    dump callbacks. Presumably, the context can then be destroyed in
    the done callback.
    
    Signed-off-by: Tom Herbert <tom at herbertland.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    (cherry-picked commit fc9e50f5a5a4e1fa9ba2756f745a13e693cf6a06)
    https://jira.sw.ru/browse/PSBM-122965
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 include/linux/netlink.h  |  2 ++
 include/net/genetlink.h  |  2 ++
 net/netlink/af_netlink.c |  4 ++++
 net/netlink/genetlink.c  | 16 ++++++++++++++++
 4 files changed, 24 insertions(+)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index a35a751..813f623 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -136,6 +136,7 @@ netlink_skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
 struct netlink_callback {
 	struct sk_buff		*skb;
 	const struct nlmsghdr	*nlh;
+	int			(*start)(struct netlink_callback *);
 	int			(*dump)(struct sk_buff * skb,
 					struct netlink_callback *cb);
 	int			(*done)(struct netlink_callback *cb);
@@ -158,6 +159,7 @@ struct nlmsghdr *
 __nlmsg_put(struct sk_buff *skb, u32 portid, u32 seq, int type, int len, int flags);
 
 struct netlink_dump_control {
+	int (*start)(struct netlink_callback *);
 	int (*dump)(struct sk_buff *skb, struct netlink_callback *);
 	int (*done)(struct netlink_callback *);
 	void *data;
diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index e33a65d..c867ebd 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -116,6 +116,7 @@ static inline void genl_info_net_set(struct genl_info *info, struct net *net)
  * @flags: flags
  * @policy: attribute validation policy
  * @doit: standard command callback
+ * @start: start callback for dumps
  * @dumpit: callback for dumpers
  * @done: completion callback for dumps
  * @ops_list: operations list
@@ -124,6 +125,7 @@ struct genl_ops {
 	const struct nla_policy	*policy;
 	int		       (*doit)(struct sk_buff *skb,
 				       struct genl_info *info);
+	int		       (*start)(struct netlink_callback *cb);
 	int		       (*dumpit)(struct sk_buff *skb,
 					 struct netlink_callback *cb);
 	int		       (*done)(struct netlink_callback *cb);
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index eb2b5de..d1db782c 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2195,6 +2195,7 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 
 	cb = &nlk->cb;
 	memset(cb, 0, sizeof(*cb));
+	cb->start = control->start;
 	cb->dump = control->dump;
 	cb->done = control->done;
 	cb->nlh = nlh;
@@ -2207,6 +2208,9 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 
 	mutex_unlock(nlk->cb_mutex);
 
+	if (cb->start)
+		cb->start(cb);
+
 	ret = netlink_dump(sk);
 	sock_put(sk);
 
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 87b4a12..5fb5884 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -472,6 +472,20 @@ void *genlmsg_put(struct sk_buff *skb, u32 portid, u32 seq,
 }
 EXPORT_SYMBOL(genlmsg_put);
 
+static int genl_lock_start(struct netlink_callback *cb)
+{
+	/* our ops are always const - netlink API doesn't propagate that */
+	const struct genl_ops *ops = cb->data;
+	int rc = 0;
+
+	if (ops->start) {
+		genl_lock();
+		rc = ops->start(cb);
+		genl_unlock();
+	}
+	return rc;
+}
+
 static int genl_lock_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	/* our ops are always const - netlink API doesn't propagate that */
@@ -544,6 +558,7 @@ static int genl_family_rcv_msg(const struct genl_family *family,
 				.module = family->module,
 				/* we have const, but the netlink API doesn't */
 				.data = (void *)ops,
+				.start = genl_lock_start,
 				.dump = genl_lock_dumpit,
 				.done = genl_lock_done,
 			};
@@ -555,6 +570,7 @@ static int genl_family_rcv_msg(const struct genl_family *family,
 		} else {
 			struct netlink_dump_control c = {
 				.module = family->module,
+				.start = ops->start,
 				.dump = ops->dumpit,
 				.done = ops->done,
 			};