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handlers.c

/*
 * lib/handlers.c default netlink message handlers
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation version 2.1
 *    of the License.
 *
 * Copyright (c) 2003-2006 Thomas Graf <tgraf@suug.ch>
 */

/**
 * @ingroup nl
 * @defgroup cb Callbacks/Customization
 * @brief
 *
 * Callbacks and overwriting capabilities are provided to take influence
 * in various control flows inside the library. All callbacks are packed
 * together in struct nl_cb which is then attached to a netlink socket or
 * passed on to the respective functions directly.
 *
 * Callbacks can control the flow of the underlying layer by returning
 * the appropriate error codes:
 * @code
 * Action ID        | Description
 * -----------------+-------------------------------------------------------
 * NL_OK       | Proceed with whatever comes next.
 * NL_SKIP          | Skip message currently being processed and continue
 *                  | with next message.
 * NL_STOP          | Stop parsing and discard all remaining messages in
 *                  | this set of messages.
 * @endcode
 *
 * All callbacks are optional and a default action is performed if no 
 * application specific implementation is provided:
 *
 * @code
 * Callback ID       | Default Return Value
 * ------------------+----------------------
 * NL_CB_VALID       | NL_OK
 * NL_CB_FINISH      | NL_STOP
 * NL_CB_OVERRUN     | NL_STOP
 * NL_CB_SKIPPED     | NL_SKIP
 * NL_CB_ACK         | NL_STOP
 * NL_CB_MSG_IN      | NL_OK
 * NL_CB_MSG_OUT     | NL_OK
 * NL_CB_INVALID     | NL_STOP
 * NL_CB_SEQ_CHECK   | NL_OK
 * NL_CB_SEND_ACK    | NL_OK
 *                   |
 * Error Callback    | NL_STOP
 * @endcode
 *
 * In order to simplify typical usages of the library, different sets of
 * default callback implementations exist:
 * @code
 * NL_CB_DEFAULT: No additional actions
 * NL_CB_VERBOSE: Automatically print warning and error messages to a file
 *                descriptor as appropriate. This is useful for CLI based
 *                applications.
 * NL_CB_DEBUG:   Print informal debugging information for each message
 *                received. This will result in every message beint sent or
 *                received to be printed to the screen in a decoded,
 *                human-readable format.
 * @endcode
 *
 * @par 1) Setting up a callback set
 * @code
 * // Allocate a callback set and initialize it to the verbose default set
 * struct nl_cb *cb = nl_cb_alloc(NL_CB_VERBOSE);
 *
 * // Modify the set to call my_func() for all valid messages
 * nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, my_func, NULL);
 *
 * // Set the error message handler to the verbose default implementation
 * // and direct it to print all errors to the given file descriptor.
 * FILE *file = fopen(...);
 * nl_cb_err(cb, NL_CB_VERBOSE, NULL, file);
 * @endcode
 * @{
 */

#include <netlink-local.h>
#include <netlink/netlink.h>
#include <netlink/utils.h>
#include <netlink/msg.h>
#include <netlink/handlers.h>

static void print_header_content(FILE *ofd, struct nlmsghdr *n)
{
      char flags[128];
      char type[32];
      
      fprintf(ofd, "type=%s length=%u flags=<%s> sequence-nr=%u pid=%u",
            nl_nlmsgtype2str(n->nlmsg_type, type, sizeof(type)),
            n->nlmsg_len, nl_nlmsg_flags2str(n->nlmsg_flags, flags,
            sizeof(flags)), n->nlmsg_seq, n->nlmsg_pid);
}

static int nl_valid_handler_verbose(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stdout;

      fprintf(ofd, "-- Warning: unhandled valid message: ");
      print_header_content(ofd, nlmsg_hdr(msg));
      fprintf(ofd, "\n");

      return NL_OK;
}

static int nl_invalid_handler_verbose(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Error: Invalid message: ");
      print_header_content(ofd, nlmsg_hdr(msg));
      fprintf(ofd, "\n");

      return NL_STOP;
}

static int nl_overrun_handler_verbose(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Error: Netlink Overrun: ");
      print_header_content(ofd, nlmsg_hdr(msg));
      fprintf(ofd, "\n");
      
      return NL_STOP;
}

static int nl_error_handler_verbose(struct sockaddr_nl *who,
                            struct nlmsgerr *e, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Error received: %s\n-- Original message: ",
            strerror(-e->error));
      print_header_content(ofd, &e->msg);
      fprintf(ofd, "\n");

      return e->error;
}

static int nl_valid_handler_debug(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Debug: Unhandled Valid message: ");
      print_header_content(ofd, nlmsg_hdr(msg));
      fprintf(ofd, "\n");

      return NL_OK;
}

static int nl_finish_handler_debug(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Debug: End of multipart message block: ");
      print_header_content(ofd, nlmsg_hdr(msg));
      fprintf(ofd, "\n");
      
      return NL_STOP;
}

static int nl_msg_in_handler_debug(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Debug: Received Message:\n");
      nl_msg_dump(msg, ofd);
      
      return NL_OK;
}

static int nl_msg_out_handler_debug(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Debug: Sent Message:\n");
      nl_msg_dump(msg, ofd);

      return NL_OK;
}

static int nl_skipped_handler_debug(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Debug: Skipped message: ");
      print_header_content(ofd, nlmsg_hdr(msg));
      fprintf(ofd, "\n");

      return NL_SKIP;
}

static int nl_ack_handler_debug(struct nl_msg *msg, void *arg)
{
      FILE *ofd = arg ? arg : stderr;

      fprintf(ofd, "-- Debug: ACK: ");
      print_header_content(ofd, nlmsg_hdr(msg));
      fprintf(ofd, "\n");

      return NL_STOP;
}

static nl_recvmsg_msg_cb_t cb_def[NL_CB_TYPE_MAX+1][NL_CB_KIND_MAX+1] = {
      [NL_CB_VALID] = {
            [NL_CB_VERBOSE]   = nl_valid_handler_verbose,
            [NL_CB_DEBUG]     = nl_valid_handler_debug,
      },
      [NL_CB_FINISH] = {
            [NL_CB_DEBUG]     = nl_finish_handler_debug,
      },
      [NL_CB_INVALID] = {
            [NL_CB_VERBOSE]   = nl_invalid_handler_verbose,
            [NL_CB_DEBUG]     = nl_invalid_handler_verbose,
      },
      [NL_CB_MSG_IN] = {
            [NL_CB_DEBUG]     = nl_msg_in_handler_debug,
      },
      [NL_CB_MSG_OUT] = {
            [NL_CB_DEBUG]     = nl_msg_out_handler_debug,
      },
      [NL_CB_OVERRUN] = {
            [NL_CB_VERBOSE]   = nl_overrun_handler_verbose,
            [NL_CB_DEBUG]     = nl_overrun_handler_verbose,
      },
      [NL_CB_SKIPPED] = {
            [NL_CB_DEBUG]     = nl_skipped_handler_debug,
      },
      [NL_CB_ACK] = {
            [NL_CB_DEBUG]     = nl_ack_handler_debug,
      },
};

static nl_recvmsg_err_cb_t cb_err_def[NL_CB_KIND_MAX+1] = {
      [NL_CB_VERBOSE]   = nl_error_handler_verbose,
      [NL_CB_DEBUG]     = nl_error_handler_verbose,
};

/**
 * @name Callback Handle Management
 * @{
 */

/**
 * Allocate a new callback handle
 * @arg kind            callback kind to be used for initialization
 * @return Newly allocated callback handle or NULL
 */
00255 struct nl_cb *nl_cb_alloc(enum nl_cb_kind kind)
{
      int i;
      struct nl_cb *cb;

      if (kind < 0 || kind > NL_CB_KIND_MAX)
            return NULL;

      cb = calloc(1, sizeof(*cb));
      if (!cb) {
            nl_errno(ENOMEM);
            return NULL;
      }

      cb->cb_refcnt = 1;

      for (i = 0; i <= NL_CB_TYPE_MAX; i++)
            nl_cb_set(cb, i, kind, NULL, NULL);

      nl_cb_err(cb, kind, NULL, NULL);

      return cb;
}

/**
 * Clone an existing callback handle
 * @arg orig            original callback handle
 * @return Newly allocated callback handle being a duplicate of
 *         orig or NULL
 */
00285 struct nl_cb *nl_cb_clone(struct nl_cb *orig)
{
      struct nl_cb *cb;
      
      cb = nl_cb_alloc(NL_CB_DEFAULT);
      if (!cb)
            return NULL;

      memcpy(cb, orig, sizeof(*orig));
      cb->cb_refcnt = 1;

      return cb;
}

struct nl_cb *nl_cb_get(struct nl_cb *cb)
{
      cb->cb_refcnt++;

      return cb;
}

void nl_cb_put(struct nl_cb *cb)
{
      if (!cb)
            return;

      cb->cb_refcnt--;

      if (cb->cb_refcnt < 0)
            BUG();

      if (cb->cb_refcnt <= 0)
            free(cb);
}

/** @} */

/**
 * @name Callback Setup
 * @{
 */

/**
 * Set up a callback 
 * @arg cb        callback set
 * @arg type            callback to modify
 * @arg kind            kind of implementation
 * @arg func            callback function (NL_CB_CUSTOM)
 * @arg arg       argument passed to callback
 *
 * @return 0 on success or a negative error code
 */
00337 int nl_cb_set(struct nl_cb *cb, enum nl_cb_type type, enum nl_cb_kind kind,
            nl_recvmsg_msg_cb_t func, void *arg)
{
      if (type < 0 || type > NL_CB_TYPE_MAX)
            return nl_error(ERANGE, "Callback type out of range");

      if (kind < 0 || kind > NL_CB_KIND_MAX)
            return nl_error(ERANGE, "Callback kind out of range");

      if (kind == NL_CB_CUSTOM) {
            cb->cb_set[type] = func;
            cb->cb_args[type] = arg;
      } else {
            cb->cb_set[type] = cb_def[type][kind];
            cb->cb_args[type] = arg;
      }

      return 0;
}

/**
 * Set up a all callbacks
 * @arg cb        callback set
 * @arg kind            kind of callback
 * @arg func            callback function
 * @arg arg       argument to be passwd to callback function
 *
 * @return 0 on success or a negative error code
 */
00366 int nl_cb_set_all(struct nl_cb *cb, enum nl_cb_kind kind,
              nl_recvmsg_msg_cb_t func, void *arg)
{
      int i, err;

      for (i = 0; i <= NL_CB_TYPE_MAX; i++) {
            err = nl_cb_set(cb, i, kind, func, arg);
            if (err < 0)
                  return err;
      }

      return 0;
}

/**
 * Set up an error callback
 * @arg cb        callback set
 * @arg kind            kind of callback
 * @arg func            callback function
 * @arg arg       argument to be passed to callback function
 */
00387 int nl_cb_err(struct nl_cb *cb, enum nl_cb_kind kind,
            nl_recvmsg_err_cb_t func, void *arg)
{
      if (kind < 0 || kind > NL_CB_KIND_MAX)
            return nl_error(ERANGE, "Callback kind out of range");

      if (kind == NL_CB_CUSTOM) {
            cb->cb_err = func;
            cb->cb_err_arg = arg;
      } else {
            cb->cb_err = cb_err_def[kind];
            cb->cb_err_arg = arg;
      }

      return 0;
}

/** @} */

/**
 * @name Overwriting
 * @{
 */

/**
 * Overwrite internal calls to nl_recvmsgs()
 * @arg cb        callback set
 * @arg func            replacement callback for nl_recvmsgs()
 */
00416 void nl_cb_overwrite_recvmsgs(struct nl_cb *cb,
                        int (*func)(struct nl_handle *, struct nl_cb *))
{
      cb->cb_recvmsgs_ow = func;
}

/**
 * Overwrite internal calls to nl_recv()
 * @arg cb        callback set
 * @arg func            replacement callback for nl_recv()
 */
00427 void nl_cb_overwrite_recv(struct nl_cb *cb,
                    int (*func)(struct nl_handle *, struct sockaddr_nl *,
                              unsigned char **, struct ucred **))
{
      cb->cb_recv_ow = func;
}

/**
 * Overwrite internal calls to nl_send()
 * @arg cb        callback set
 * @arg func            replacement callback for nl_send()
 */
00439 void nl_cb_overwrite_send(struct nl_cb *cb,
                    int (*func)(struct nl_handle *, struct nl_msg *))
{
      cb->cb_send_ow = func;
}

/** @} */

/** @} */

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