docs: convert vpp doc md->rst

Type: improvement

Change-Id: If453321785b04f9c16e8cea36fb1910efaeb2c59
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>

1 files changed, 404 insertions, 0 deletions

diff --git a/src/tools/vppapigen/VPPAPI.rst b/src/tools/vppapigen/VPPAPI.rst
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+VPP API Language
+================
+
+The VPP binary API is a message passing API. The VPP API language is
+used to define a RPC interface between VPP and its control plane. The
+API messages supports shared memory transport and Unix domain sockets
+(SOCK_STREAM).
+
+The wire format is essentially that of a network formatted (big-endian)
+packed C struct.
+
+The VPP API compiler is located in *src/tools/vppapigen* and can
+currently compile to JSON or C (used by the VPP binary itself).
+
+Language definition
+-------------------
+
+Defining a messages
+~~~~~~~~~~~~~~~~~~~
+
+There are 3 types of message exchanges:
+
+-  Request/Reply The client sends a request message and the server
+   replies with a single reply message. The convention is that the reply
+   message is named as method_name + \_reply.
+
+-  Dump/Detail The client sends a “bulk” request message to the server,
+   and the server replies with a set of detail messages. These messages
+   may be of different type. A dump/detail call must be enclosed in a
+   control ping block (Otherwise the client will not know the end of the
+   bulk transmission). The method name must end with method + “\_dump”,
+   the reply message should be named method + “\_details”. The exception
+   here is for the methods that return multiple message types
+   (e.g. sw_interface_dump). The Dump/Detail methods are typically used
+   for acquiring bulk information, like the complete FIB table.
+
+-  Events The client can register for getting asynchronous notifications
+   from the server. This is useful for getting interface state changes,
+   and so on. The method name for requesting notifications is
+   conventionally prefixed with “want\_”. E.g. “want_interface_events”.
+   Which notification types results from an event registration is
+   defined in the service definition.
+
+A message from a client must include the ‘client_index’, an opaque
+cookie identifying the sender, and a ‘context’ field to let the client
+match request with reply.
+
+An example of a message definition. The client sends the show_version
+request, the server replies with the show_version_reply.
+
+The *client_index* and *context* fields are required in all requests.
+The *context* is returned by the server and is used by the client to
+match up request and reply messages.
+
+.. code-block:: c
+
+   define show_version
+   {
+     u32 client_index;
+     u32 context;
+   };
+   define show_version_reply
+   {
+     u32 context;
+     i32 retval;
+     string program [32];
+     string version [32];
+     string build_date [32];
+     /* The final field can be a variable length argument */
+     string build_directory [];
+   };
+
+The flags are not used by the clients, but have special meaning for some
+of the tracing and debugging of the API. The *autoreply* flag is a
+shorthand for a reply message with just a *retval* field.
+
+.. code-block:: c
+
+       define : DEFINE ID '{' block_statements_opt '}' ';'
+       define : flist DEFINE ID '{' block_statements_opt '}' ';'
+       flist : flag
+             | flist flag
+       flag : MANUAL_PRINT
+            | MANUAL_ENDIAN
+            | DONT_TRACE
+            | AUTOREPLY
+
+       block_statements_opt : block_statements
+       block_statements : block_statement
+                        | block_statements block_statement
+       block_statement : declaration
+                       | option
+       declaration : type_specifier ID ';'
+                   | type_specifier ID '[' ID '=' assignee ']' ';'
+       declaration : type_specifier ID '[' NUM ']' ';'
+                   | type_specifier ID '[' ID ']' ';'
+       type_specifier : U8
+                      | U16
+                      | U32
+                      | U64
+                      | I8
+                      | I16
+                      | I32
+                      | I64
+                      | F64
+                      | BOOL
+                      | STRING
+       type_specifier : ID
+
+Options
+~~~~~~~
+
+The *option* word is used to specify meta information. The only current
+use is to specify a semantic version of the .api file itself.
+
+Example:
+
+.. code-block:: c
+
+   option version = "1.0.0";
+
+.. code-block:: c
+
+
+       option : OPTION ID '=' assignee ';'
+       assignee : NUM
+                | TRUE
+                | FALSE
+                | STRING_LITERAL
+
+Defining new types
+~~~~~~~~~~~~~~~~~~
+
+New user defined types are defined just like messages. A typedef has two
+forms. It can either define an alias for a different type (or array).
+
+Example:
+
+.. code-block:: c
+
+   typedef u8 ip4_address[4];
+   typedef u8 ip6_address[16];
+
+Where the above defines two new types *vl_api_ip4_address_t* and
+*vl_api_ip6_address_t*. These are aliases for the underlying u8 array.
+
+In the other form, it is used to specify an abstract data type.
+
+.. code-block:: c
+
+   enum address_family {
+     ADDRESS_IP4 = 0,
+     ADDRESS_IP6,
+   };
+
+   union address_union {
+     vl_api_ip4_address_t ip4;
+     vl_api_ip6_address_t ip6;
+   };
+
+   typedef address {
+     vl_api_address_family_t af;
+     vl_api_address_union_t un;
+   };
+
+Where the new type *vl_api_address_t*
+
+.. code-block:: c
+
+       typedef : TYPEDEF ID '{' block_statements_opt '}' ';'
+       typedef : TYPEDEF declaration
+
+Importing Definitions
+~~~~~~~~~~~~~~~~~~~~~
+
+You can use definitions from other .api files by importing them. To
+import another .api’s definitions, you add an import statement to the
+top of your file:
+
+import “vnet/ip/ip_types.api”;
+
+By default you can only use definitions from directly imported .api
+files.
+
+The API compiler searches for imported files in a set of directories
+specified on the API compiler command line using the –includedir flag.
+
+.. code-block:: c
+
+   import : IMPORT STRING_LITERAL ';'
+
+Comments
+~~~~~~~~
+
+The API language uses C style comments.
+
+.. code-block:: c
+
+   /* */
+   //
+
+Enumerations
+~~~~~~~~~~~~
+
+Enums are similar to enums in C.
+
+Every enum definition must contain a constant that maps to zero as its
+first element. This is because:
+
+There must be a zero value, so that we can use 0 as a numeric default
+value. The zero value needs to be the first element.
+
+As in C, enums can be used as flags or just as numbers. The on-wire, and
+in memory representation size of an enum can be specified. Not all
+language bindings will support that. The default size is 4 (u32).
+
+Example
+
+.. code-block:: c
+
+   enum ip_neighbor_flags
+   {
+     IP_API_NEIGHBOR_FLAG_NONE = 0,
+     IP_API_NEIGHBOR_FLAG_STATIC = 0x1,
+     IP_API_NEIGHBOR_FLAG_NO_FIB_ENTRY = 0x2,
+   };
+
+Which generates the vl_api_ip_neighbor_flags_t in the C binding. In
+Python that is represented as an IntFlag object
+VppEnum.vl_api_ip_neighbor_flags_t.
+
+.. code-block:: c
+
+       enum : ENUM ID '{' enum_statements '}' ';'
+       enum : ENUM ID ':' enum_size '{' enum_statements '}' ';'
+       enum_size : U8
+                 | U16
+                 | U32
+       enum_statements : enum_statement
+                       | enum_statements enum_statement
+       enum_statement : ID '=' NUM ','
+                      | ID ','
+
+Services
+~~~~~~~~
+
+The service statement defines the relationship between messages. For
+request/response and dump/details messages it ties the request with the
+reply. For events, it specifies which events that can be received for a
+given ``want_*`` call.
+
+Example:
+
+.. code-block:: c
+
+   service {
+     rpc want_interface_events returns want_interface_events_reply
+       events sw_interface_event;
+   };
+
+Which states that the request want_interface_events returns a
+want_interface_events_reply and if enabled the client will receive
+sw_interface_event messages whenever interface states changes.
+
+.. code-block:: c
+
+       service : SERVICE '{' service_statements '}' ';'
+       service_statements : service_statement
+                       | service_statements service_statement
+       service_statement : RPC ID RETURNS NULL ';'
+                            | RPC ID RETURNS ID ';'
+                            | RPC ID RETURNS STREAM ID ';'
+                            | RPC ID RETURNS ID EVENTS event_list ';'
+       event_list : events
+                  | event_list events
+       events : ID
+              | ID ','
+
+Types
+-----
+
+Scalar Value Types
+~~~~~~~~~~~~~~~~~~
+
+========= ======== =============== ===========
+.api type size     C type          Python type
+========= ======== =============== ===========
+i8        1        i8              int
+u8        1        u8              int
+i16       2        i16             int
+u16       2        u16             int
+i32       4        i32             int
+u32       4        u32             int
+i64       8        i64             int
+u64       8        u64             int
+f64       8        f64             float
+bool      1        bool            boolean
+string    variable vl_api_string_t str
+========= ======== =============== ===========
+
+User Defined Types
+~~~~~~~~~~~~~~~~~~
+
+vnet/ip/ip_types.api
+^^^^^^^^^^^^^^^^^^^^
+
++--------------------+--------+-------------+-------------------------+
+| .api type          | size   | C type      | Python type             |
++====================+========+=============+=========================+
+| vl_api_address_t   | 20     | vl_ap       | `                       |
+|                    |        | i_address_t | `<class 'ipaddress.IPv4 |
+|                    |        |             | Address'> or <class 'ip |
+|                    |        |             | address.IPv6Address'>`` |
++--------------------+--------+-------------+-------------------------+
+| vl                 | 4      | vl_api_ip   | ``<class 'ip            |
+| _api_ip4_address_t |        | 4_address_t | address.IPv4Address'>`` |
++--------------------+--------+-------------+-------------------------+
+| vl                 | 16     | vl_api_ip   | ``<class 'ip            |
+| _api_ip6_address_t |        | 6_address_t | address.IPv6Address'>`` |
++--------------------+--------+-------------+-------------------------+
+| vl_api_prefix_t    | 21     | vl_a        | `                       |
+|                    |        | pi_prefix_t | `<class 'ipaddress.IPv4 |
+|                    |        |             | Network'> or <class 'ip |
+|                    |        |             | address.IPv6Network'>`` |
++--------------------+--------+-------------+-------------------------+
+| v                  | 5      | vl_api_i    | ``<class 'ip            |
+| l_api_ip4_prefix_t |        | p4_prefix_t | address.IPv4Network'>`` |
++--------------------+--------+-------------+-------------------------+
+| v                  | 17     | vl_api_i    | ``<class 'ip            |
+| l_api_ip6_prefix_t |        | p6_prefix_t | address.IPv6Network'>`` |
++--------------------+--------+-------------+-------------------------+
+| vl_api_ip4_add     | 5      | vl_api_ip4  | ``<class 'ipad          |
+| ress_with_prefix_t |        | _address_wi | dress.IPv4Interface'>`` |
+|                    |        | th_prefix_t |                         |
++--------------------+--------+-------------+-------------------------+
+| vl_api_ip6_add     | 17     | vl_api_ip6  | ``<class 'ipad          |
+| ress_with_prefix_t |        | _address_wi | dress.IPv6Interface'>`` |
+|                    |        | th_prefix_t |                         |
++--------------------+--------+-------------+-------------------------+
+
+vnet/ethernet/ethernet_types.api
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
++---------------------+------+---------------------+-------------------+
+| .api type           | size | C type              | Python type       |
++=====================+======+=====================+===================+
+| ``vl_               | 6    | ``vl_               | ``class 'vpp_pa   |
+| api_mac_address_t`` |      | api_mac_address_t`` | pi.MACAddress'>`` |
++---------------------+------+---------------------+-------------------+
+
+vnet/interface_types.api
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+======================== ==== ======================== ===========
+.api type                size C type                   Python type
+======================== ==== ======================== ===========
+vl_api_interface_index_t 4    vl_api_interface_index_t int
+======================== ==== ======================== ===========
+
+New explicit types
+~~~~~~~~~~~~~~~~~~
+
+String versus bytes
+^^^^^^^^^^^^^^^^^^^
+
+A byte string with a maximum length of 64:
+
+.. code-block:: c
+
+   u8 name[64];
+
+Before the “string” type was added, text string were defined like this.
+The implications of that was the user would have to know if the field
+represented a \\0 ended C-string or a fixed length byte string. The wire
+format of the ‘string’ type is a u32 length
+
+An IPv4 or IPv6 address was previously defined like:
+
+.. code-block:: c
+
+   u8 is_ip6;
+   u8 address[16];
+
+Which made it hard for language bindings to represent the address as
+anything but a byte string. The new explicit address types are shown
+above.
+
+Language generators
+-------------------
+
+The VPP API compiler currently has two output modules. One generating
+JSON and one generating C header files that are directly used by the VPP
+infrastructure and plugins.
+
+The C/C++, Python, Go Lua, and Java language bindings are generated
+based on the JSON files.
+
+Future considerations
+~~~~~~~~~~~~~~~~~~~~~
+
+-  Generate C/C++ (vapi) client code directly from vppapigen
+-  Embed JSON definitions into the API server, so dynamic languages
+   can download them directly without going via the filesystem and JSON
+   files.