diff options
Diffstat (limited to 'Documentation/connector/connector.txt')
-rw-r--r-- | Documentation/connector/connector.txt | 119 |
1 files changed, 61 insertions, 58 deletions
diff --git a/Documentation/connector/connector.txt b/Documentation/connector/connector.txt index ad6e0ba7b38c..81e6bf6ead57 100644 --- a/Documentation/connector/connector.txt +++ b/Documentation/connector/connector.txt | |||
@@ -5,10 +5,10 @@ Kernel Connector. | |||
5 | Kernel connector - new netlink based userspace <-> kernel space easy | 5 | Kernel connector - new netlink based userspace <-> kernel space easy |
6 | to use communication module. | 6 | to use communication module. |
7 | 7 | ||
8 | Connector driver adds possibility to connect various agents using | 8 | The Connector driver makes it easy to connect various agents using a |
9 | netlink based network. One must register callback and | 9 | netlink based network. One must register a callback and an identifier. |
10 | identifier. When driver receives special netlink message with | 10 | When the driver receives a special netlink message with the appropriate |
11 | appropriate identifier, appropriate callback will be called. | 11 | identifier, the appropriate callback will be called. |
12 | 12 | ||
13 | From the userspace point of view it's quite straightforward: | 13 | From the userspace point of view it's quite straightforward: |
14 | 14 | ||
@@ -17,10 +17,10 @@ From the userspace point of view it's quite straightforward: | |||
17 | send(); | 17 | send(); |
18 | recv(); | 18 | recv(); |
19 | 19 | ||
20 | But if kernelspace want to use full power of such connections, driver | 20 | But if kernelspace wants to use the full power of such connections, the |
21 | writer must create special sockets, must know about struct sk_buff | 21 | driver writer must create special sockets, must know about struct sk_buff |
22 | handling... Connector allows any kernelspace agents to use netlink | 22 | handling, etc... The Connector driver allows any kernelspace agents to use |
23 | based networking for inter-process communication in a significantly | 23 | netlink based networking for inter-process communication in a significantly |
24 | easier way: | 24 | easier way: |
25 | 25 | ||
26 | int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *)); | 26 | int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *)); |
@@ -32,15 +32,15 @@ struct cb_id | |||
32 | __u32 val; | 32 | __u32 val; |
33 | }; | 33 | }; |
34 | 34 | ||
35 | idx and val are unique identifiers which must be registered in | 35 | idx and val are unique identifiers which must be registered in the |
36 | connector.h for in-kernel usage. void (*callback) (void *) - is a | 36 | connector.h header for in-kernel usage. void (*callback) (void *) is a |
37 | callback function which will be called when message with above idx.val | 37 | callback function which will be called when a message with above idx.val |
38 | will be received by connector core. Argument for that function must | 38 | is received by the connector core. The argument for that function must |
39 | be dereferenced to struct cn_msg *. | 39 | be dereferenced to struct cn_msg *. |
40 | 40 | ||
41 | struct cn_msg | 41 | struct cn_msg |
42 | { | 42 | { |
43 | struct cb_id id; | 43 | struct cb_id id; |
44 | 44 | ||
45 | __u32 seq; | 45 | __u32 seq; |
46 | __u32 ack; | 46 | __u32 ack; |
@@ -55,92 +55,95 @@ Connector interfaces. | |||
55 | 55 | ||
56 | int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *)); | 56 | int cn_add_callback(struct cb_id *id, char *name, void (*callback) (void *)); |
57 | 57 | ||
58 | Registers new callback with connector core. | 58 | Registers new callback with connector core. |
59 | 59 | ||
60 | struct cb_id *id - unique connector's user identifier. | 60 | struct cb_id *id - unique connector's user identifier. |
61 | It must be registered in connector.h for legal in-kernel users. | 61 | It must be registered in connector.h for legal in-kernel users. |
62 | char *name - connector's callback symbolic name. | 62 | char *name - connector's callback symbolic name. |
63 | void (*callback) (void *) - connector's callback. | 63 | void (*callback) (void *) - connector's callback. |
64 | Argument must be dereferenced to struct cn_msg *. | 64 | Argument must be dereferenced to struct cn_msg *. |
65 | 65 | ||
66 | |||
66 | void cn_del_callback(struct cb_id *id); | 67 | void cn_del_callback(struct cb_id *id); |
67 | 68 | ||
68 | Unregisters new callback with connector core. | 69 | Unregisters new callback with connector core. |
70 | |||
71 | struct cb_id *id - unique connector's user identifier. | ||
69 | 72 | ||
70 | struct cb_id *id - unique connector's user identifier. | ||
71 | 73 | ||
72 | int cn_netlink_send(struct cn_msg *msg, u32 __groups, int gfp_mask); | 74 | int cn_netlink_send(struct cn_msg *msg, u32 __groups, int gfp_mask); |
73 | 75 | ||
74 | Sends message to the specified groups. It can be safely called from | 76 | Sends message to the specified groups. It can be safely called from |
75 | softirq context, but may silently fail under strong memory pressure. | 77 | softirq context, but may silently fail under strong memory pressure. |
76 | If there are no listeners for given group -ESRCH can be returned. | 78 | If there are no listeners for given group -ESRCH can be returned. |
77 | 79 | ||
78 | struct cn_msg * - message header(with attached data). | 80 | struct cn_msg * - message header(with attached data). |
79 | u32 __group - destination group. | 81 | u32 __group - destination group. |
80 | If __group is zero, then appropriate group will | 82 | If __group is zero, then appropriate group will |
81 | be searched through all registered connector users, | 83 | be searched through all registered connector users, |
82 | and message will be delivered to the group which was | 84 | and message will be delivered to the group which was |
83 | created for user with the same ID as in msg. | 85 | created for user with the same ID as in msg. |
84 | If __group is not zero, then message will be delivered | 86 | If __group is not zero, then message will be delivered |
85 | to the specified group. | 87 | to the specified group. |
86 | int gfp_mask - GFP mask. | 88 | int gfp_mask - GFP mask. |
87 | 89 | ||
88 | Note: When registering new callback user, connector core assigns | 90 | Note: When registering new callback user, connector core assigns |
89 | netlink group to the user which is equal to it's id.idx. | 91 | netlink group to the user which is equal to it's id.idx. |
90 | 92 | ||
91 | /*****************************************/ | 93 | /*****************************************/ |
92 | Protocol description. | 94 | Protocol description. |
93 | /*****************************************/ | 95 | /*****************************************/ |
94 | 96 | ||
95 | Current offers transport layer with fixed header. Recommended | 97 | The current framework offers a transport layer with fixed headers. The |
96 | protocol which uses such header is following: | 98 | recommended protocol which uses such a header is as following: |
97 | 99 | ||
98 | msg->seq and msg->ack are used to determine message genealogy. When | 100 | msg->seq and msg->ack are used to determine message genealogy. When |
99 | someone sends message it puts there locally unique sequence and random | 101 | someone sends a message, they use a locally unique sequence and random |
100 | acknowledge numbers. Sequence number may be copied into | 102 | acknowledge number. The sequence number may be copied into |
101 | nlmsghdr->nlmsg_seq too. | 103 | nlmsghdr->nlmsg_seq too. |
102 | 104 | ||
103 | Sequence number is incremented with each message to be sent. | 105 | The sequence number is incremented with each message sent. |
104 | 106 | ||
105 | If we expect reply to our message, then sequence number in received | 107 | If you expect a reply to the message, then the sequence number in the |
106 | message MUST be the same as in original message, and acknowledge | 108 | received message MUST be the same as in the original message, and the |
107 | number MUST be the same + 1. | 109 | acknowledge number MUST be the same + 1. |
108 | 110 | ||
109 | If we receive message and it's sequence number is not equal to one we | 111 | If we receive a message and its sequence number is not equal to one we |
110 | are expecting, then it is new message. If we receive message and it's | 112 | are expecting, then it is a new message. If we receive a message and |
111 | sequence number is the same as one we are expecting, but it's | 113 | its sequence number is the same as one we are expecting, but its |
112 | acknowledge is not equal acknowledge number in original message + 1, | 114 | acknowledge is not equal to the acknowledge number in the original |
113 | then it is new message. | 115 | message + 1, then it is a new message. |
114 | 116 | ||
115 | Obviously, protocol header contains above id. | 117 | Obviously, the protocol header contains the above id. |
116 | 118 | ||
117 | connector allows event notification in the following form: kernel | 119 | The connector allows event notification in the following form: kernel |
118 | driver or userspace process can ask connector to notify it when | 120 | driver or userspace process can ask connector to notify it when |
119 | selected id's will be turned on or off(registered or unregistered it's | 121 | selected ids will be turned on or off (registered or unregistered its |
120 | callback). It is done by sending special command to connector | 122 | callback). It is done by sending a special command to the connector |
121 | driver(it also registers itself with id={-1, -1}). | 123 | driver (it also registers itself with id={-1, -1}). |
122 | 124 | ||
123 | As example of usage Documentation/connector now contains cn_test.c - | 125 | As example of this usage can be found in the cn_test.c module which |
124 | testing module which uses connector to request notification and to | 126 | uses the connector to request notification and to send messages. |
125 | send messages. | ||
126 | 127 | ||
127 | /*****************************************/ | 128 | /*****************************************/ |
128 | Reliability. | 129 | Reliability. |
129 | /*****************************************/ | 130 | /*****************************************/ |
130 | 131 | ||
131 | Netlink itself is not reliable protocol, that means that messages can | 132 | Netlink itself is not a reliable protocol. That means that messages can |
132 | be lost due to memory pressure or process' receiving queue overflowed, | 133 | be lost due to memory pressure or process' receiving queue overflowed, |
133 | so caller is warned must be prepared. That is why struct cn_msg [main | 134 | so caller is warned that it must be prepared. That is why the struct |
134 | connector's message header] contains u32 seq and u32 ack fields. | 135 | cn_msg [main connector's message header] contains u32 seq and u32 ack |
136 | fields. | ||
135 | 137 | ||
136 | /*****************************************/ | 138 | /*****************************************/ |
137 | Userspace usage. | 139 | Userspace usage. |
138 | /*****************************************/ | 140 | /*****************************************/ |
141 | |||
139 | 2.6.14 has a new netlink socket implementation, which by default does not | 142 | 2.6.14 has a new netlink socket implementation, which by default does not |
140 | allow to send data to netlink groups other than 1. | 143 | allow people to send data to netlink groups other than 1. |
141 | So, if to use netlink socket (for example using connector) | 144 | So, if you wish to use a netlink socket (for example using connector) |
142 | with different group number userspace application must subscribe to | 145 | with a different group number, the userspace application must subscribe to |
143 | that group. It can be achieved by following pseudocode: | 146 | that group first. It can be achieved by the following pseudocode: |
144 | 147 | ||
145 | s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR); | 148 | s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR); |
146 | 149 | ||
@@ -160,8 +163,8 @@ if (bind(s, (struct sockaddr *)&l_local, sizeof(struct sockaddr_nl)) == -1) { | |||
160 | } | 163 | } |
161 | 164 | ||
162 | Where 270 above is SOL_NETLINK, and 1 is a NETLINK_ADD_MEMBERSHIP socket | 165 | Where 270 above is SOL_NETLINK, and 1 is a NETLINK_ADD_MEMBERSHIP socket |
163 | option. To drop multicast subscription one should call above socket option | 166 | option. To drop a multicast subscription, one should call the above socket |
164 | with NETLINK_DROP_MEMBERSHIP parameter which is defined as 0. | 167 | option with the NETLINK_DROP_MEMBERSHIP parameter which is defined as 0. |
165 | 168 | ||
166 | 2.6.14 netlink code only allows to select a group which is less or equal to | 169 | 2.6.14 netlink code only allows to select a group which is less or equal to |
167 | the maximum group number, which is used at netlink_kernel_create() time. | 170 | the maximum group number, which is used at netlink_kernel_create() time. |