General documentation updates

- We now have several developer-focused docs, so create an index page
  for them.
- Rework several docs to fit into the index structure.
- Experiment with code highlighting; tweak the CSS slightly to make
  it slightly nicer to look at.

Change-Id: I4185a18f84fa0764745ca7a3148276064a3155c6
Signed-off-by: Chris Luke <chrisy@flirble.org>
(cherry picked from commit 64ebb5ff1338140d94c7f9ee72138fe84d89de2e)

1 files changed, 219 insertions, 0 deletions

diff --git a/extras/libmemif/docs/gettingstarted_doc.md b/extras/libmemif/docs/gettingstarted_doc.md
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+## Getting started    {#libmemif_gettingstarted_doc}
+
+#### Concept (Connecting to VPP)
+
+For detailed information on api calls and structures please refer to @ref libmemif.h.
+
+1. Initialize memif
+   - Declare callback function handling file descriptor event polling.
+```C
+int
+control_fd_update (int fd, uint8_t events)
+{
+...
+}
+```
+   - Call memif initialization function. memif\_init
+```C
+err = memif_init (control_fd_update, APP_NAME);
+```
+   
+> If event occurres on any file descriptor returned by this callback, call memif\_control\_fd\_handler function.
+```C
+memif_err = memif_control_fd_handler (evt.data.fd, events);
+``` 
+> If callback function parameter for memif\_init function is set to NULL, libmemif will handle file descriptor event polling.
+  Api call memif\_poll\_event will call epoll\_pwait with user defined timeout to poll event on file descriptors opened by libmemif.
+```C
+/* main loop */
+    while (1)
+    {
+        if (memif_poll_event (-1) < 0)
+        {
+            DBG ("poll_event error!");
+        }
+    }
+```
+    
+> Memif initialization function will initialize internal structures and create timer file descriptor, which will be used for sending periodic connection requests. Timer is disarmed if no memif interface is created.
+ 
+2. Creating interface
+   - Declare memif connction handle.
+```C
+memif_conn_handle_t c;
+```
+> example app uses struct that contains connection handle, rx/tx buffers and other connection specific information.
+
+   - Specify connection arguments.
+```C
+memif_conn_args_t args;
+memset (&args, 0, sizeof (args));
+args.is_master = is_master;
+args.log2_ring_size = 10;
+args.buffer_size = 2048;
+args.num_s2m_rings = 2;
+args.num_m2s_rings = 2;
+strncpy ((char *) args.interface_name, IF_NAME, strlen (IF_NAME));
+strncpy ((char *) args.instance_name, APP_NAME, strlen (APP_NAME));
+args.mode = 0;
+args.interface_id = 0;
+```
+   - Declare callback functions called on connected/disconnected/interrupted status changed.
+```C
+int
+on_connect (memif_conn_handle_t conn, void *private_ctx)
+{
+...
+}
+
+int
+on_disconnect (memif_conn_handle_t conn, void *private_ctx)
+{
+    INFO ("memif connected!");
+    return 0;
+}
+```
+   - Call memif interface create function. memif\_create
+```C
+err = memif_create (&c->conn,
+        &args, on_connect, on_disconnect, on_interrupt, &ctx[index]);
+```
+> If connection is in slave mode, arms timer file descriptor.
+> If on interrupt callback is set to NULL, user will not be notified about interrupt. Use memif\_get\_queue\_efd call to get interrupt file descriptor for specific queue.
+```C
+int fd = -1;
+err = memif_get_queue_efd (c->conn, data->qid, &fd);
+```
+
+3. Connection establishment
+    - User application will poll events on all file descriptors returned in memif\_control\_fd\_update\_t callback.
+    - On event call memif\_control\_fd\_handler.
+    - Everything else regarding connection establishment will be done internally.
+    - Once connection has been established, a callback will inform the user about connection status change.
+
+4. Interrupt packet receive
+    - If event is polled on interrupt file descriptor, libmemif will call memif\_interrupt\_t callback specified for every connection instance.
+```C
+int
+on_interrupt (memif_conn_handle_t conn, void *private_ctx, uint16_t qid)
+{
+...
+}
+```
+
+6. Memif buffers
+    - Packet data are stored in memif\_buffer\_t. Pointer _data_ points to shared memory buffer, and unsigned integer *data\_len* contains packet data length.
+```C
+typedef struct
+{
+    uint16_t desc_index;
+    uint32_t buffer_len;
+    uint32_t data_len;
+    void *data;
+} memif_buffer_t;
+```
+
+5. Packet receive
+    - Api call memif\_rx\_burst will set all required fields in memif buffers provided by user application.
+```C
+err = memif_rx_burst (c->conn, qid, c->rx_bufs, MAX_MEMIF_BUFS, &rx);
+```
+    - User application can then process packets.
+    - Api call memif\_buffer\_free will make supplied memif buffers ready for next receive and mark shared memory buffers as free.
+```C
+err = memif_buffer_free (c->conn, qid, c->rx_bufs, rx, &fb);
+```
+
+6. Packet transmit
+    - Api call memif\_buffer\_alloc will set all required fields in memif buffers provided by user application.
+```C
+err = memif_buffer_alloc (c->conn, qid, c->tx_bufs, n, &r);
+```
+    - User application can populate shared memory buffers with packets.
+    - Api call memif\_tx\_burst will inform peer interface (master memif on VPP) that there are packets ready to receive and mark memif buffers as free.
+```C
+err = memif_tx_burst (c->conn, qid, c->tx_bufs, c->tx_buf_num, &r);
+```
+
+7. Helper functions
+    - Memif details
+      - Api call memif\_get\_details will return details about connection.
+```C
+err = memif_get_details (c->conn, &md, buf, buflen);
+```
+    - Memif error messages
+      - Every api call returns error code (integer value) mapped to error string.
+      - Call memif\_strerror will return error message assigned to specific error code.
+```C
+if (err != MEMIF_ERR_SUCCESS)
+    INFO ("memif_get_details: %s", memif_strerror (err));
+```
+        - Not all syscall errors are translated to memif error codes. If error code 1 (MEMIF\_ERR\_SYSCALL) is returned then libmemif needs to be compiled with -DMEMIF_DBG flag to print error message. Use _make -B_ to rebuild libmemif in debug mode.
+
+#### Example app (libmemif fd event polling):
+
+- @ref extras/libmemif/examples/icmp_responder
+
+> Optional argument: transmit queue id.
+```
+icmpr 1
+```
+> Set transmit queue id to 1. Default is 0.
+> Application will create memif interface in slave mode and try to connect to VPP. Exit using Ctrl+C. Application will handle SIGINT signal, free allocated memory and exit with EXIT_SUCCESS.
+
+#### Example app:
+
+ICMP Responder custom fd event polling.
+
+- @ref extras/libmemif/examples/icmp_responder-epoll
+
+#### Example app (multi-thread queue polling)
+
+ICMP Responder multi-thread.
+- @ref extras/libmemif/examples/icmp_responder-mt
+
+> Simple example of libmemif multi-thread usage. Connection establishment is handled by main thread. There are two rx queues in this example. One in polling mode and second in interrupt mode.
+
+VPP config:
+```
+# create memif id 0 master
+# set int state memif0 up
+# set int ip address memif0 192.168.1.1/24
+# ping 192.168.1.2
+```
+For multiple rings (queues) support run VPP with worker threads:
+example startup.conf:
+```
+unix {
+  interactive
+  nodaemon 
+  full-coredump
+}
+
+cpu {
+  workers 2
+}
+```
+VPP config:
+```
+# create memif id 0 master
+# set int state memif0 up
+# set int ip address memif0 192.168.1.1/24
+# ping 192.168.1.2
+```
+> Master mode queue number is limited by worker threads. Slave mode interface needs to specify number of queues.
+```
+# create memif id 0 slave rx-queues 2 tx-queues 2
+```
+> Example applications use VPP default socket file for memif: /run/vpp/memif.sock
+> For master mode, socket directory must exist prior to memif\_create call.
+
+#### Unit tests
+
+Unit tests use [Check](https://libcheck.github.io/check/index.html) framework. This framework must be installed in order to build *unit\_test* binary.
+Ubuntu/Debian:
+```
+sudo apt-get install check
+```
+[More platforms](https://libcheck.github.io/check/web/install.html)
+