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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
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>
-rw-r--r--include/linux/netlink.h2
-rw-r--r--include/net/genetlink.h32
-rw-r--r--include/net/netlink.h24
-rw-r--r--net/netlink/af_netlink.c2
4 files changed, 60 insertions, 0 deletions
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 4c4ac3f3ce5..8d1bcec5cc0 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -48,6 +48,7 @@ struct nlmsghdr {
#define NLM_F_MULTI 2 /* Multipart message, terminated by NLMSG_DONE */
#define NLM_F_ACK 4 /* Reply with ack, with zero or error code */
#define NLM_F_ECHO 8 /* Echo this request */
+#define NLM_F_DUMP_INTR 16 /* Dump was inconsistent due to sequence change */
/* Modifiers to GET request */
#define NLM_F_ROOT 0x100 /* specify tree root */
@@ -221,6 +222,7 @@ struct netlink_callback {
struct netlink_callback *cb);
int (*done)(struct netlink_callback *cb);
int family;
+ unsigned int prev_seq, seq;
long args[6];
};
diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index d420f28b6d6..82d8d09faa4 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -160,6 +160,38 @@ static inline void *genlmsg_put(struct sk_buff *skb, u32 pid, u32 seq,
}
/**
+ * genlmsg_nlhdr - Obtain netlink header from user specified header
+ * @user_hdr: user header as returned from genlmsg_put()
+ * @family: generic netlink family
+ *
+ * Returns pointer to netlink header.
+ */
+static inline struct nlmsghdr *genlmsg_nlhdr(void *user_hdr,
+ struct genl_family *family)
+{
+ return (struct nlmsghdr *)((char *)user_hdr -
+ family->hdrsize -
+ GENL_HDRLEN -
+ NLMSG_HDRLEN);
+}
+
+/**
+ * genl_dump_check_consistent - check if sequence is consistent and advertise if not
+ * @cb: netlink callback structure that stores the sequence number
+ * @user_hdr: user header as returned from genlmsg_put()
+ * @family: generic netlink family
+ *
+ * Cf. nl_dump_check_consistent(), this just provides a wrapper to make it
+ * simpler to use with generic netlink.
+ */
+static inline void genl_dump_check_consistent(struct netlink_callback *cb,
+ void *user_hdr,
+ struct genl_family *family)
+{
+ nl_dump_check_consistent(cb, genlmsg_nlhdr(user_hdr, family));
+}
+
+/**
* genlmsg_put_reply - Add generic netlink header to a reply message
* @skb: socket buffer holding the message
* @info: receiver info
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
**************************************************************************/
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 6ef64adf736..a7ec8512f55 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1693,6 +1693,8 @@ static int netlink_dump(struct sock *sk)
if (!nlh)
goto errout_skb;
+ nl_dump_check_consistent(cb, nlh);
+
memcpy(nlmsg_data(nlh), &len, sizeof(len));
if (sk_filter(sk, skb))