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docs: connector: convert to ReST and rename to connector.rst
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As it has some function definitions, move them to connector.h.

The remaining conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <[email protected]>
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mchehab committed Jul 15, 2019
1 parent 387b146 commit 720594f
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130 changes: 45 additions & 85 deletions Documentation/connector/connector.txt → Documentation/connector/connector.rst
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Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
/*****************************************/
Kernel Connector.
/*****************************************/
:orphan:

================
Kernel Connector
================

Kernel connector - new netlink based userspace <-> kernel space easy
to use communication module.
Expand All @@ -12,94 +14,55 @@ identifier, the appropriate callback will be called.

From the userspace point of view it's quite straightforward:

socket();
bind();
send();
recv();
- socket();
- bind();
- send();
- recv();

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:
easier way::

int cn_add_callback(struct cb_id *id, char *name, void (*callback) (struct cn_msg *, struct netlink_skb_parms *));
void cn_netlink_send_multi(struct cn_msg *msg, u16 len, u32 portid, u32 __group, int gfp_mask);
void cn_netlink_send(struct cn_msg *msg, u32 portid, u32 __group, int gfp_mask);
int cn_add_callback(struct cb_id *id, char *name, void (*callback) (struct cn_msg *, struct netlink_skb_parms *));
void cn_netlink_send_multi(struct cn_msg *msg, u16 len, u32 portid, u32 __group, int gfp_mask);
void cn_netlink_send(struct cn_msg *msg, u32 portid, u32 __group, int gfp_mask);

struct cb_id
{
struct cb_id
{
__u32 idx;
__u32 val;
};
};

idx and val are unique identifiers which must be registered in the
connector.h header for in-kernel usage. void (*callback) (void *) is a
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 *.
be dereferenced to `struct cn_msg *`::

struct cn_msg
{
struct cn_msg
{
struct cb_id id;

__u32 seq;
__u32 ack;

__u32 len; /* Length of the following data */
__u32 len; /* Length of the following data */
__u8 data[0];
};

/*****************************************/
Connector interfaces.
/*****************************************/

int cn_add_callback(struct cb_id *id, char *name, void (*callback) (struct cn_msg *, struct netlink_skb_parms *));

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) (struct cn..) - connector's callback.
cn_msg and the sender's credentials


void cn_del_callback(struct cb_id *id);

Unregisters new callback with connector core.

struct cb_id *id - unique connector's user identifier.


int cn_netlink_send_multi(struct cn_msg *msg, u16 len, u32 portid, u32 __groups, int gfp_mask);
int cn_netlink_send(struct cn_msg *msg, u32 portid, 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.
Connector interfaces
====================

struct cn_msg * - message header(with attached data).
u16 len - for *_multi multiple cn_msg messages can be sent
u32 port - destination port.
If non-zero the message will be sent to the
given port, which should be set to the
original sender.
u32 __group - destination group.
If port and __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.
.. kernel-doc:: include/linux/connector.h

Note: When registering new callback user, connector core assigns
netlink group to the user which is equal to its id.idx.
Note:
When registering new callback user, connector core assigns
netlink group to the user which is equal to its id.idx.

/*****************************************/
Protocol description.
/*****************************************/
Protocol description
====================

The current framework offers a transport layer with fixed headers. The
recommended protocol which uses such a header is as following:
Expand Down Expand Up @@ -132,42 +95,40 @@ driver (it also registers itself with id={-1, -1}).
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.
/*****************************************/
Reliability
===========

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 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.
/*****************************************/
Userspace usage
===============

2.6.14 has a new netlink socket implementation, which by default does not
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:
that group first. It can be achieved by the following pseudocode::

s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);

l_local.nl_family = AF_NETLINK;
l_local.nl_groups = 12345;
l_local.nl_pid = 0;
l_local.nl_family = AF_NETLINK;
l_local.nl_groups = 12345;
l_local.nl_pid = 0;

if (bind(s, (struct sockaddr *)&l_local, sizeof(struct sockaddr_nl)) == -1) {
if (bind(s, (struct sockaddr *)&l_local, sizeof(struct sockaddr_nl)) == -1) {
perror("bind");
close(s);
return -1;
}
}

{
{
int on = l_local.nl_groups;
setsockopt(s, 270, 1, &on, sizeof(on));
}
}

Where 270 above is SOL_NETLINK, and 1 is a NETLINK_ADD_MEMBERSHIP socket
option. To drop a multicast subscription, one should call the above socket
Expand All @@ -180,16 +141,15 @@ group number 12345, you must increment CN_NETLINK_USERS to that number.
Additional 0xf numbers are allocated to be used by non-in-kernel users.

Due to this limitation, group 0xffffffff does not work now, so one can
not use add/remove connector's group notifications, but as far as I know,
not use add/remove connector's group notifications, but as far as I know,
only cn_test.c test module used it.

Some work in netlink area is still being done, so things can be changed in
2.6.15 timeframe, if it will happen, documentation will be updated for that
kernel.

/*****************************************/
Code samples
/*****************************************/
============

Sample code for a connector test module and user space can be found
in samples/connector/. To build this code, enable CONFIG_CONNECTOR
Expand Down
2 changes: 1 addition & 1 deletion drivers/w1/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ config W1_CON
default y
---help---
This allows to communicate with userspace using connector. For more
information see <file:Documentation/connector/connector.txt>.
information see <file:Documentation/connector/connector.rst>.
There are three types of messages between w1 core and userspace:
1. Events. They are generated each time new master or slave device found
either due to automatic or requested search.
Expand Down
63 changes: 62 additions & 1 deletion include/linux/connector.h
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Original file line number Diff line number Diff line change
Expand Up @@ -55,10 +55,71 @@ struct cn_dev {
struct cn_queue_dev *cbdev;
};

/**
* cn_add_callback() - Registers new callback with connector core.
*
* @id: unique connector's user identifier.
* It must be registered in connector.h for legal
* in-kernel users.
* @name: connector's callback symbolic name.
* @callback: connector's callback.
* parameters are %cn_msg and the sender's credentials
*/
int cn_add_callback(struct cb_id *id, const char *name,
void (*callback)(struct cn_msg *, struct netlink_skb_parms *));
void cn_del_callback(struct cb_id *);
/**
* cn_del_callback() - Unregisters new callback with connector core.
*
* @id: unique connector's user identifier.
*/
void cn_del_callback(struct cb_id *id);


/**
* cn_netlink_send_mult - Sends message to the specified groups.
*
* @msg: message header(with attached data).
* @len: Number of @msg to be sent.
* @portid: destination port.
* If non-zero the message will be sent to the given port,
* which should be set to the original sender.
* @group: destination group.
* If @portid and @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.
* @gfp_mask: GFP mask.
*
* 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.
*/
int cn_netlink_send_mult(struct cn_msg *msg, u16 len, u32 portid, u32 group, gfp_t gfp_mask);

/**
* cn_netlink_send_mult - Sends message to the specified groups.
*
* @msg: message header(with attached data).
* @portid: destination port.
* If non-zero the message will be sent to the given port,
* which should be set to the original sender.
* @group: destination group.
* If @portid and @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.
* @gfp_mask: GFP mask.
*
* 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.
*/
int cn_netlink_send(struct cn_msg *msg, u32 portid, u32 group, gfp_t gfp_mask);

int cn_queue_add_callback(struct cn_queue_dev *dev, const char *name,
Expand Down
2 changes: 1 addition & 1 deletion samples/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -99,7 +99,7 @@ config SAMPLE_CONNECTOR
When enabled, this builds both a sample kernel module for
the connector interface and a user space tool to communicate
with it.
See also Documentation/connector/connector.txt
See also Documentation/connector/connector.rst

config SAMPLE_HIDRAW
bool "hidraw sample"
Expand Down

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