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+/**
+@page tevent_data Chapter 3: Accessing data
+@section data Accessing data with tevent
+
+A tevent request is (usually) created together with a structure for storing the
+data necessary for an asynchronous computation. For these private data, tevent
+library uses void (generic) pointers, therefore any data type can be very
+simply pointed at. However, this attitude requires clear and guaranteed
+knowledge of the data type that will be handled, in advance. Private data can
+be of 2 types: connected with a request itself or given as an individual
+argument to a callback. It is necessary to differentiate these types, because
+there is a slightly different method of data access for each. There are two
+possibilities how to access data that is given as an argument directly to a
+callback. The difference lies in the pointer that is returned. In one case it
+is the data type specified in the function’s argument, in another void* is
+returned.
+
+@code
+void tevent_req_callback_data (struct tevent_req *req, #type)
+void tevent_req_callback_data_void (struct tevent_req *req)
+@endcode
+
+
+To obtain data that are strictly bound to a request, this function is the only
+direct procedure.
+
+@code
+void *tevent_req_data (struct tevent_req *req, #type)
+@endcode
+
+Example with both calls which differs between private data within tevent
+request and data handed over as an argument.
+
+@code
+#include <stdio.h>
+#include <unistd.h>
+#include <tevent.h>
+
+struct foo_state {
+    int x;
+};
+
+struct testA {
+    int y;
+};
+
+
+static void foo_done(struct tevent_req *req) {
+    // a->x contains 10 since it came from foo_send
+    struct foo_state *a = tevent_req_data(req, struct foo_state);
+
+    // b->y contains 9 since it came from run
+    struct testA *b = tevent_req_callback_data(req, struct testA);
+
+    // c->y contains 9 since it came from run we just used a different way
+    // of getting it.
+    struct testA *c = (struct testA *)tevent_req_callback_data_void(req);
+
+    printf("a->x: %d\n", a->x);
+    printf("b->y: %d\n", b->y);
+    printf("c->y: %d\n", c->y);
+}
+
+
+struct tevent_req * foo_send(TALLOC_CTX *mem_ctx, struct tevent_context *event_ctx) {
+
+printf("_send\n");
+struct tevent_req *req;
+struct foo_state *state;
+
+req = tevent_req_create(event_ctx, &state, struct foo_state);
+state->x = 10;
+
+return req;
+}
+
+static void run(struct tevent_context *ev, struct tevent_timer *te,
+                struct timeval current_time, void *private_data) {
+    struct tevent_req *req;
+    struct testA *tmp = talloc(ev, struct testA);
+
+    // Note that we did not use the private data passed in
+
+    tmp->y = 9;
+    req = foo_send(ev, ev);
+
+    tevent_req_set_callback(req, foo_done, tmp);
+    tevent_req_done(req);
+
+}
+
+int main (int argc, char **argv) {
+
+    struct tevent_context *event_ctx;
+    struct testA *data;
+    TALLOC_CTX *mem_ctx;
+    struct tevent_timer *time_event;
+
+    mem_ctx = talloc_new(NULL); //parent
+    if (mem_ctx == NULL)
+        return EXIT_FAILURE;
+
+    event_ctx = tevent_context_init(mem_ctx);
+    if (event_ctx == NULL)
+        return EXIT_FAILURE;
+
+    data = talloc(mem_ctx, struct testA);
+    data->y = 11;
+
+    time_event = tevent_add_timer(event_ctx,
+                                  mem_ctx,
+                                  tevent_timeval_current(),
+                                  run,
+                                  data);
+    if (time_event == NULL) {
+        fprintf(stderr, " FAILED\n");
+        return EXIT_FAILURE;
+    }
+
+    tevent_loop_once(event_ctx);
+
+    talloc_free(mem_ctx);
+
+    printf("Quit\n");
+    return EXIT_SUCCESS;
+}
+@endcode
+
+Output of this example is:
+
+@code
+a->x: 10
+b->y: 9
+c->y: 9
+@endcode
+
+*/