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Commit 670dc283 authored by Johannes Berg's avatar Johannes Berg Committed by John W. Linville
Browse files

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: default avatarJohannes Berg <johannes.berg@intel.com>
Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
parent c1c3daee

include/linux/netlink.h

+2 −0
Original line number Diff line number Diff line
@@ -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];

};

include/net/genetlink.h

+32 −0
Original line number Diff line number Diff line
@@ -159,6 +159,38 @@ static inline void *genlmsg_put(struct sk_buff *skb, u32 pid, u32 seq, 
	return (char *) hdr + GENL_HDRLEN;

}



/**

 * 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

include/net/netlink.h

+24 −0
Original line number Diff line number Diff line
@@ -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

 **************************************************************************/

net/netlink/af_netlink.c

+2 −0
Original line number Diff line number Diff line
@@ -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))