|
@@ -5,10 +5,10 @@ Kernel Connector.
|
|
|
Kernel connector - new netlink based userspace <-> kernel space easy
|
|
|
to use communication module.
|
|
|
|
|
|
-Connector driver adds possibility to connect various agents using
|
|
|
-netlink based network. One must register callback and
|
|
|
-identifier. When driver receives special netlink message with
|
|
|
-appropriate identifier, appropriate callback will be called.
|
|
|
+The Connector driver makes it easy to connect various agents using a
|
|
|
+netlink based network. One must register a callback and an identifier.
|
|
|
+When the driver receives a special netlink message with the appropriate
|
|
|
+identifier, the appropriate callback will be called.
|
|
|
|
|
|
From the userspace point of view it's quite straightforward:
|
|
|
|
|
@@ -17,10 +17,10 @@ From the userspace point of view it's quite straightforward:
|
|
|
send();
|
|
|
recv();
|
|
|
|
|
|
-But if kernelspace want to use full power of such connections, driver
|
|
|
-writer must create special sockets, must know about struct sk_buff
|
|
|
-handling... Connector allows any kernelspace agents to use netlink
|
|
|
-based networking for inter-process communication in a significantly
|
|
|
+But if kernelspace wants to use the full power of such connections, the
|
|
|
+driver writer must create special sockets, must know about struct sk_buff
|
|
|
+handling, etc... The Connector driver allows any kernelspace agents to use
|
|
|
+netlink based networking for inter-process communication in a significantly
|
|
|
easier way:
|
|
|
|
|
|
int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *));
|
|
@@ -32,15 +32,15 @@ struct cb_id
|
|
|
__u32 val;
|
|
|
};
|
|
|
|
|
|
-idx and val are unique identifiers which must be registered in
|
|
|
-connector.h for in-kernel usage. void (*callback) (void *) - is a
|
|
|
-callback function which will be called when message with above idx.val
|
|
|
-will be received by connector core. Argument for that function must
|
|
|
+idx and val are unique identifiers which must be registered in the
|
|
|
+connector.h header for in-kernel usage. void (*callback) (void *) is a
|
|
|
+callback function which will be called when a message with above idx.val
|
|
|
+is received by the connector core. The argument for that function must
|
|
|
be dereferenced to struct cn_msg *.
|
|
|
|
|
|
struct cn_msg
|
|
|
{
|
|
|
- struct cb_id id;
|
|
|
+ struct cb_id id;
|
|
|
|
|
|
__u32 seq;
|
|
|
__u32 ack;
|
|
@@ -55,92 +55,95 @@ Connector interfaces.
|
|
|
|
|
|
int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *));
|
|
|
|
|
|
-Registers new callback with connector core.
|
|
|
+ Registers new callback with connector core.
|
|
|
|
|
|
-struct cb_id *id - unique connector's user identifier.
|
|
|
- It must be registered in connector.h for legal in-kernel users.
|
|
|
-char *name - connector's callback symbolic name.
|
|
|
-void (*callback) (void *) - connector's callback.
|
|
|
+ struct cb_id *id - unique connector's user identifier.
|
|
|
+ It must be registered in connector.h for legal in-kernel users.
|
|
|
+ char *name - connector's callback symbolic name.
|
|
|
+ void (*callback) (void *) - connector's callback.
|
|
|
Argument must be dereferenced to struct cn_msg *.
|
|
|
|
|
|
+
|
|
|
void cn_del_callback(struct cb_id *id);
|
|
|
|
|
|
-Unregisters new callback with connector core.
|
|
|
+ Unregisters new callback with connector core.
|
|
|
+
|
|
|
+ struct cb_id *id - unique connector's user identifier.
|
|
|
|
|
|
-struct cb_id *id - unique connector's user identifier.
|
|
|
|
|
|
int cn_netlink_send(struct cn_msg *msg, u32 __groups, int gfp_mask);
|
|
|
|
|
|
-Sends message to the specified groups. It can be safely called from
|
|
|
-softirq context, but may silently fail under strong memory pressure.
|
|
|
-If there are no listeners for given group -ESRCH can be returned.
|
|
|
+ Sends message to the specified groups. It can be safely called from
|
|
|
+ softirq context, but may silently fail under strong memory pressure.
|
|
|
+ If there are no listeners for given group -ESRCH can be returned.
|
|
|
|
|
|
-struct cn_msg * - message header(with attached data).
|
|
|
-u32 __group - destination group.
|
|
|
+ struct cn_msg * - message header(with attached data).
|
|
|
+ u32 __group - destination group.
|
|
|
If __group is zero, then appropriate group will
|
|
|
be searched through all registered connector users,
|
|
|
and message will be delivered to the group which was
|
|
|
created for user with the same ID as in msg.
|
|
|
If __group is not zero, then message will be delivered
|
|
|
to the specified group.
|
|
|
-int gfp_mask - GFP mask.
|
|
|
+ int gfp_mask - GFP mask.
|
|
|
|
|
|
-Note: When registering new callback user, connector core assigns
|
|
|
-netlink group to the user which is equal to it's id.idx.
|
|
|
+ Note: When registering new callback user, connector core assigns
|
|
|
+ netlink group to the user which is equal to it's id.idx.
|
|
|
|
|
|
/*****************************************/
|
|
|
Protocol description.
|
|
|
/*****************************************/
|
|
|
|
|
|
-Current offers transport layer with fixed header. Recommended
|
|
|
-protocol which uses such header is following:
|
|
|
+The current framework offers a transport layer with fixed headers. The
|
|
|
+recommended protocol which uses such a header is as following:
|
|
|
|
|
|
msg->seq and msg->ack are used to determine message genealogy. When
|
|
|
-someone sends message it puts there locally unique sequence and random
|
|
|
-acknowledge numbers. Sequence number may be copied into
|
|
|
+someone sends a message, they use a locally unique sequence and random
|
|
|
+acknowledge number. The sequence number may be copied into
|
|
|
nlmsghdr->nlmsg_seq too.
|
|
|
|
|
|
-Sequence number is incremented with each message to be sent.
|
|
|
+The sequence number is incremented with each message sent.
|
|
|
|
|
|
-If we expect reply to our message, then sequence number in received
|
|
|
-message MUST be the same as in original message, and acknowledge
|
|
|
-number MUST be the same + 1.
|
|
|
+If you expect a reply to the message, then the sequence number in the
|
|
|
+received message MUST be the same as in the original message, and the
|
|
|
+acknowledge number MUST be the same + 1.
|
|
|
|
|
|
-If we receive message and it's sequence number is not equal to one we
|
|
|
-are expecting, then it is new message. If we receive message and it's
|
|
|
-sequence number is the same as one we are expecting, but it's
|
|
|
-acknowledge is not equal acknowledge number in original message + 1,
|
|
|
-then it is new message.
|
|
|
+If we receive a message and its sequence number is not equal to one we
|
|
|
+are expecting, then it is a new message. If we receive a message and
|
|
|
+its sequence number is the same as one we are expecting, but its
|
|
|
+acknowledge is not equal to the acknowledge number in the original
|
|
|
+message + 1, then it is a new message.
|
|
|
|
|
|
-Obviously, protocol header contains above id.
|
|
|
+Obviously, the protocol header contains the above id.
|
|
|
|
|
|
-connector allows event notification in the following form: kernel
|
|
|
+The connector allows event notification in the following form: kernel
|
|
|
driver or userspace process can ask connector to notify it when
|
|
|
-selected id's will be turned on or off(registered or unregistered it's
|
|
|
-callback). It is done by sending special command to connector
|
|
|
-driver(it also registers itself with id={-1, -1}).
|
|
|
+selected ids will be turned on or off (registered or unregistered its
|
|
|
+callback). It is done by sending a special command to the connector
|
|
|
+driver (it also registers itself with id={-1, -1}).
|
|
|
|
|
|
-As example of usage Documentation/connector now contains cn_test.c -
|
|
|
-testing module which uses connector to request notification and to
|
|
|
-send messages.
|
|
|
+As example of this usage can be found in the cn_test.c module which
|
|
|
+uses the connector to request notification and to send messages.
|
|
|
|
|
|
/*****************************************/
|
|
|
Reliability.
|
|
|
/*****************************************/
|
|
|
|
|
|
-Netlink itself is not reliable protocol, that means that messages can
|
|
|
+Netlink itself is not a reliable protocol. That means that messages can
|
|
|
be lost due to memory pressure or process' receiving queue overflowed,
|
|
|
-so caller is warned must be prepared. That is why struct cn_msg [main
|
|
|
-connector's message header] contains u32 seq and u32 ack fields.
|
|
|
+so caller is warned that it must be prepared. That is why the struct
|
|
|
+cn_msg [main connector's message header] contains u32 seq and u32 ack
|
|
|
+fields.
|
|
|
|
|
|
/*****************************************/
|
|
|
Userspace usage.
|
|
|
/*****************************************/
|
|
|
+
|
|
|
2.6.14 has a new netlink socket implementation, which by default does not
|
|
|
-allow to send data to netlink groups other than 1.
|
|
|
-So, if to use netlink socket (for example using connector)
|
|
|
-with different group number userspace application must subscribe to
|
|
|
-that group. It can be achieved by following pseudocode:
|
|
|
+allow people to send data to netlink groups other than 1.
|
|
|
+So, if you wish to use a netlink socket (for example using connector)
|
|
|
+with a different group number, the userspace application must subscribe to
|
|
|
+that group first. It can be achieved by the following pseudocode:
|
|
|
|
|
|
s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
|
|
|
|
|
@@ -160,8 +163,8 @@ if (bind(s, (struct sockaddr *)&l_local, sizeof(struct sockaddr_nl)) == -1) {
|
|
|
}
|
|
|
|
|
|
Where 270 above is SOL_NETLINK, and 1 is a NETLINK_ADD_MEMBERSHIP socket
|
|
|
-option. To drop multicast subscription one should call above socket option
|
|
|
-with NETLINK_DROP_MEMBERSHIP parameter which is defined as 0.
|
|
|
+option. To drop a multicast subscription, one should call the above socket
|
|
|
+option with the NETLINK_DROP_MEMBERSHIP parameter which is defined as 0.
|
|
|
|
|
|
2.6.14 netlink code only allows to select a group which is less or equal to
|
|
|
the maximum group number, which is used at netlink_kernel_create() time.
|