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authorJohannes Berg <johannes.berg@intel.com>2011-06-20 13:40:46 +0200
committerJohn W. Linville <linville@tuxdriver.com>2011-06-22 16:09:45 -0400
commit670dc2833d144375eac36ad74111495a825a9288 (patch)
tree12d5d3a925da562a6ba0497c47f4b55c71ff545b /include/net/netlink.h
parentc1c3daee97498f5d74bfd23531cfe23c8e14a619 (diff)
netlink: advertise incomplete dumps
Consider the following situation: * a dump that would show 8 entries, four in the first round, and four in the second * between the first and second rounds, 6 entries are removed * now the second round will not show any entry, and even if there is a sequence/generation counter the application will not know To solve this problem, add a new flag NLM_F_DUMP_INTR to the netlink header that indicates the dump wasn't consistent, this flag can also be set on the MSG_DONE message that terminates the dump, and as such above situation can be detected. To achieve this, add a sequence counter to the netlink callback struct. Of course, netlink code still needs to use this new functionality. The correct way to do that is to always set cb->seq when a dumpit callback is invoked and call nl_dump_check_consistent() for each new message. The core code will also call this function for the final MSG_DONE message. To make it usable with generic netlink, a new function genlmsg_nlhdr() is needed to obtain the netlink header from the genetlink user header. Signed-off-by: Johannes Berg <johannes.berg@intel.com> Acked-by: David S. Miller <davem@davemloft.net> Signed-off-by: John W. Linville <linville@tuxdriver.com>
Diffstat (limited to 'include/net/netlink.h')
-rw-r--r--include/net/netlink.h24
1 files changed, 24 insertions, 0 deletions
diff --git a/include/net/netlink.h b/include/net/netlink.h
index 02740a94f10..98c185441be 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -638,6 +638,30 @@ static inline int nlmsg_unicast(struct sock *sk, struct sk_buff *skb, u32 pid)
nlmsg_ok(pos, rem); \
pos = nlmsg_next(pos, &(rem)))
+/**
+ * nl_dump_check_consistent - check if sequence is consistent and advertise if not
+ * @cb: netlink callback structure that stores the sequence number
+ * @nlh: netlink message header to write the flag to
+ *
+ * This function checks if the sequence (generation) number changed during dump
+ * and if it did, advertises it in the netlink message header.
+ *
+ * The correct way to use it is to set cb->seq to the generation counter when
+ * all locks for dumping have been acquired, and then call this function for
+ * each message that is generated.
+ *
+ * Note that due to initialisation concerns, 0 is an invalid sequence number
+ * and must not be used by code that uses this functionality.
+ */
+static inline void
+nl_dump_check_consistent(struct netlink_callback *cb,
+ struct nlmsghdr *nlh)
+{
+ if (cb->prev_seq && cb->seq != cb->prev_seq)
+ nlh->nlmsg_flags |= NLM_F_DUMP_INTR;
+ cb->prev_seq = cb->seq;
+}
+
/**************************************************************************
* Netlink Attributes
**************************************************************************/