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author | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-06-27 15:39:22 -0300 |
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committer | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-07-15 11:03:02 -0300 |
commit | baa293e9544bea71361950d071579f0e4d5713ed (patch) | |
tree | 29e0400c806016783a3fd7a380be40a201956653 /Documentation/connector | |
parent | 4f4cfa6c560c93ba180c30675cf845e1597de44c (diff) | |
download | linux-baa293e9544bea71361950d071579f0e4d5713ed.tar.bz2 |
docs: driver-api: add a series of orphaned documents
There are lots of documents under Documentation/*.txt and a few other
orphan documents elsehwere that belong to the driver-API book.
Move them to their right place.
Reviewed-by: Cornelia Huck <cohuck@redhat.com> # vfio-related parts
Acked-by: Logan Gunthorpe <logang@deltatee.com> # switchtec
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Diffstat (limited to 'Documentation/connector')
-rw-r--r-- | Documentation/connector/connector.rst | 156 |
1 files changed, 0 insertions, 156 deletions
diff --git a/Documentation/connector/connector.rst b/Documentation/connector/connector.rst deleted file mode 100644 index 24e26dc22dbf..000000000000 --- a/Documentation/connector/connector.rst +++ /dev/null @@ -1,156 +0,0 @@ -:orphan: - -================ -Kernel Connector -================ - -Kernel connector - new netlink based userspace <-> kernel space easy -to use communication module. - -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: - - - 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:: - - 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 - { - __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 -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; - - __u32 seq; - __u32 ack; - - __u32 len; /* Length of the following data */ - __u8 data[0]; - }; - -Connector interfaces -==================== - - .. 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. - -Protocol description -==================== - -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 a message, they use a locally unique sequence and random -acknowledge number. The sequence number may be copied into -nlmsghdr->nlmsg_seq too. - -The sequence number is incremented with each message sent. - -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 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 sequence number in the original -message + 1, then it is a new message. - -Obviously, the protocol header contains the above id. - -The connector allows event notification in the following form: kernel -driver or userspace process can ask connector to notify it when -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 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 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 -=============== - -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:: - - s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR); - - 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) { - 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 -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. -In case of connector it is CN_NETLINK_USERS + 0xf, so if you want to use -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, -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 -and CONFIG_SAMPLES. |