Cache Implementation

Data Structures
struct	nl_msgtype
	Message type to cache action association. More...
struct	nl_af_group
	Address family to netlink group association. More...
struct	nl_parser_param
	Parser parameters. More...
struct	nl_cache_ops
	Cache Operations. More...

Macros
#define	NL_ACT_MAX   (__NL_ACT_MAX - 1)
#define	END_OF_MSGTYPES_LIST   { -1, -1, NULL }
#define	END_OF_GROUP_LIST   AF_UNSPEC, 0

Enumerations
enum	{   NL_ACT_UNSPEC,   NL_ACT_NEW,   NL_ACT_DEL,   NL_ACT_GET,   NL_ACT_SET,   NL_ACT_CHANGE,   __NL_ACT_MAX }

Functions
void	nl_cache_ops_get (struct nl_cache_ops *)
	Increment reference counter.
void	nl_cache_ops_put (struct nl_cache_ops *)
	Decrement reference counter.

---

Detailed Description

1) Cache Definition

   struct nl_cache_ops my_cache_ops = {
        .co_name                = "route/link",
        .co_protocol            = NETLINK_ROUTE,
        .co_hdrsize             = sizeof(struct ifinfomsg),
        .co_obj_ops             = &my_obj_ops,
   };

2)

   // The simplest way to fill a cache is by providing a request-update
   // function which must trigger a complete dump on the kernel-side of
   // whatever the cache covers.
   static int my_request_update(struct nl_cache *cache,
                                struct nl_sock *socket)
   {
        // In this example, we request a full dump of the interface table
        return nl_rtgen_request(socket, RTM_GETLINK, AF_UNSPEC, NLM_F_DUMP);
   }
  
   // The resulting netlink messages sent back will be fed into a message
   // parser one at a time. The message parser has to extract all relevant
   // information from the message and create an object reflecting the
   // contents of the message and pass it on to the parser callback function
   // provide which will add the object to the cache.
   static int my_msg_parser(struct nl_cache_ops *ops, struct sockaddr_nl *who,
                            struct nlmsghdr *nlh, struct nl_parser_param *pp)
   {
        struct my_obj *obj;
  
        obj = my_obj_alloc();
        obj->ce_msgtype = nlh->nlmsg_type;
  
        // Parse the netlink message and continue creating the object.
  
        err = pp->pp_cb((struct nl_object *) obj, pp);
        if (err < 0)
                goto errout;
   }
  
   struct nl_cache_ops my_cache_ops = {
        ...
        .co_request_update      = my_request_update,
        .co_msg_parser          = my_msg_parser,
   };

3) Notification based Updates

   // Caches can be kept up-to-date based on notifications if the kernel
   // sends out notifications whenever an object is added/removed/changed.
   //
   // It is trivial to support this, first a list of groups needs to be
   // defined which are required to join in order to receive all necessary
   // notifications. The groups are separated by address family to support
   // the common situation where a separate group is used for each address
   // family. If there is only one group, simply specify AF_UNSPEC.
   static struct nl_af_group addr_groups[] = {
        { AF_INET,      RTNLGRP_IPV4_IFADDR },
        { AF_INET6,     RTNLGRP_IPV6_IFADDR },
        { END_OF_GROUP_LIST },
   };
  
   // In order for the caching system to know the meaning of each message
   // type it requires a table which maps each supported message type to
   // a cache action, e.g. RTM_NEWADDR means address has been added or
   // updated, RTM_DELADDR means address has been removed.
   static struct nl_cache_ops rtnl_addr_ops = {
        ...
        .co_msgtypes            = {
                                        { RTM_NEWADDR, NL_ACT_NEW, "new" },
                                        { RTM_DELADDR, NL_ACT_DEL, "del" },
                                        { RTM_GETADDR, NL_ACT_GET, "get" },
                                        END_OF_MSGTYPES_LIST,
                                },
        .co_groups              = addr_groups,
   };
  
   // It is now possible to keep the cache up-to-date using the cache manager.

---

Function Documentation

void nl_cache_ops_get

(

struct nl_cache_ops *

ops

)

Increment reference counter.

Parameters:

ops	Cache operations

Definition at line 56 of file cache_mngt.c.

References nl_cache_ops::co_refcnt.

Referenced by nl_cache_mngt_provide(), nl_cache_ops_associate_safe(), and nl_cache_ops_lookup_safe().

Here is the caller graph for this function:

void nl_cache_ops_put

(

struct nl_cache_ops *

ops

)

Decrement reference counter.

Parameters:

ops	Cache operations

Definition at line 65 of file cache_mngt.c.

References nl_cache_ops::co_refcnt.

Referenced by nl_cache_alloc_name(), nl_cache_mngr_add(), nl_cache_mngt_unprovide(), nl_msg_dump(), and nl_object_alloc_name().

Here is the caller graph for this function: