device: allow to use dummy as a way to test streamer

This adds loopback tests via `tests/`

device/dummy/buffer_list.c

@@ -1,25 +1,69 @@
 #include "dummy.h"
 #include "device/buffer_list.h"
+#include "device/device.h"
+#include "util/opts/log.h"
 
 #include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
 
 int dummy_buffer_list_open(buffer_list_t *buf_list)
 {
+  int fd = -1;
+
   buf_list->dummy = calloc(1, sizeof(buffer_list_dummy_t));
-  return 0;
+  buf_list->dummy->fds[0] = -1;
+  buf_list->dummy->fds[1] = -1;
+
+  if (!buf_list->do_capture) {
+    LOG_ERROR(buf_list, "Only capture mode supported");
+  }
+
+  if (pipe2(buf_list->dummy->fds, O_DIRECT|O_CLOEXEC) < 0) {
+    LOG_INFO(buf_list, "Cannot open `pipe2`.");
+    return -1;
+  }
+
+  fd = open(buf_list->dev->path, O_RDWR|O_NONBLOCK);
+  if (fd < 0) {
+		LOG_ERROR(buf_list, "Can't open device: %s", buf_list->dev->path);
+  }
+
+  struct stat st;
+  if (fstat(fd, &st) < 0) {
+		LOG_ERROR(buf_list, "Can't get fstat: %s", buf_list->dev->path);
+  }
+
+  buf_list->dummy->data = malloc(st.st_size);
+  if (!buf_list->dummy->data) {
+		LOG_ERROR(buf_list, "Can't allocate %ld bytes for %s", st.st_size, buf_list->dev->path);
+  }
+
+  buf_list->dummy->length = read(fd, buf_list->dummy->data, st.st_size);
+  if (!buf_list->dummy->data) {
+		LOG_ERROR(buf_list, "Can't read %ld bytes for %s. Only read %zu.", st.st_size, buf_list->dev->path, buf_list->dummy->length);
+  }
+
+  close(fd);
+  return buf_list->fmt.nbufs;
+
+error:
+  close(fd);
+  return -1;
 }
 
 void dummy_buffer_list_close(buffer_list_t *buf_list)
 {
-  free(buf_list->dummy);
-}
+  if (buf_list->dummy) {
+    close(buf_list->dummy->fds[0]);
+    close(buf_list->dummy->fds[1]);
+    free(buf_list->dummy->data);
+  }
 
-int dummy_buffer_list_set_buffers(buffer_list_t *buf_list, int nbufs)
-{
-  return -1;
+  free(buf_list->dummy);
 }
 
 int dummy_buffer_list_set_stream(buffer_list_t *buf_list, bool do_on)
 {
-  return -1;
+  return 0;
 }