Return-path: Received: from he.sipsolutions.net ([78.46.109.217]:46617 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751875Ab1FTLku (ORCPT ); Mon, 20 Jun 2011 07:40:50 -0400 Subject: [PATCH] netlink: advertise incomplete dumps From: Johannes Berg To: netdev , linux-wireless Cc: Samuel Ortiz , "aloisio.almeida" , John Linville , Thomas Graf Content-Type: text/plain; charset="UTF-8" Date: Mon, 20 Jun 2011 13:40:46 +0200 Message-ID: <1308570046.4322.5.camel@jlt3.sipsolutions.net> (sfid-20110620_134105_286141_FBFB4948) Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: From: Johannes Berg 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 --- Should we merge this through wireless? From wireless-next it'll go into net-next quickly, but the converse isn't true, so using it in wireless would be harder if it was merged through net-next I think? Or John can cherry-pick into wireless-testing? include/linux/netlink.h | 2 ++ include/net/genetlink.h | 32 ++++++++++++++++++++++++++++++++ include/net/netlink.h | 24 ++++++++++++++++++++++++ net/netlink/af_netlink.c | 2 ++ 4 files changed, 60 insertions(+) --- a/include/linux/netlink.h 2011-06-20 08:42:41.000000000 +0200 +++ b/include/linux/netlink.h 2011-06-20 09:39:19.000000000 +0200 @@ -49,6 +49,7 @@ 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 */ @@ -222,6 +223,7 @@ struct netlink_callback { struct netlink_callback *cb); int (*done)(struct netlink_callback *cb); int family; + unsigned int prev_seq, seq; long args[6]; }; --- a/net/netlink/af_netlink.c 2011-06-20 08:42:41.000000000 +0200 +++ b/net/netlink/af_netlink.c 2011-06-20 09:39:19.000000000 +0200 @@ -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)) --- a/include/net/genetlink.h 2011-06-20 08:42:41.000000000 +0200 +++ b/include/net/genetlink.h 2011-06-20 13:36:54.000000000 +0200 @@ -160,6 +160,38 @@ static inline void *genlmsg_put(struct s } /** + * 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 --- a/include/net/netlink.h 2011-06-20 08:42:41.000000000 +0200 +++ b/include/net/netlink.h 2011-06-20 09:39:19.000000000 +0200 @@ -638,6 +638,30 @@ static inline int nlmsg_unicast(struct s 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 **************************************************************************/