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>
This commit is contained in:
Johannes Berg 2011-06-20 13:40:46 +02:00 committed by John W. Linville
parent c1c3daee97
commit 670dc2833d
4 changed files with 60 additions and 0 deletions

View File

@ -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];
};

View File

@ -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

View File

@ -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
**************************************************************************/

View File

@ -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))