ts_core: do not reuse file-entries to avoid wrong callback activation

If file callback modified another file callback (unregister(old fd),
close(old fd), open => new fd (new fd == old fd), register(new fd)),
and that other file callback was triggered in same 'poll' call instance,
the wrong file callback (for 'new fd') would be incorrectly called.

Avoid issue by not reusing file-entries when registering new file
callbacks.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@haltian.com>

apps/thingsee/lib/ts_core.c

@@ -1219,7 +1219,6 @@ int __ts_core_fd_register(const int fd, const pollevent_t events,
 {
   struct ts_core_s * ts_core = &g_ts_core;
   struct file_s * file;
-  bool reuse = false;
 
   /* Check input parameters */
 
@@ -1246,9 +1245,10 @@ int __ts_core_fd_register(const int fd, const pollevent_t events,
               return ERROR;
             }
 
-          reuse = true;
-
-          goto reuse_file;
+          /* We used to 'reuse' entry here. We must not do this, as
+           * new 'fd' might not be for same device instance as the original
+           * 'file->fd'. Setting 'active' could activate callback too early
+           * if poll result handling loop is being currently processed. */
         }
 
       /* Move to next file */
@@ -1258,7 +1258,7 @@ int __ts_core_fd_register(const int fd, const pollevent_t events,
 
   /* Allocate memory for file */
 
-  file = malloc(sizeof(struct file_s));
+  file = calloc(1, sizeof(struct file_s));
   if (!file)
     {
       set_errno(ENOMEM);
@@ -1266,8 +1266,6 @@ int __ts_core_fd_register(const int fd, const pollevent_t events,
       return ERROR;
     }
 
-reuse_file:
-
   /* Setup file descriptor for monitoring */
 
   file->fd = fd;
@@ -1277,12 +1275,9 @@ reuse_file:
   file->priv = priv;
   file->reg_func_name = reg_func_name;
 
-  if (!reuse)
-    {
   /* Add file to file descriptor queue */
 
   sq_addlast(&file->entry, &ts_core->files);
-    }
 
   return OK;
 }