rework fallocate logic

src/fs_fallocate.cpp

@@ -0,0 +1,44 @@
+/*
+  Copyright (c) 2016, Antonio SJ Musumeci <trapexit@spawn.link>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include <errno.h>
+#include <fcntl.h>
+
+#include "fs_fallocate.hpp"
+
+namespace fs
+{
+  int
+  fallocate(const int   fd,
+            const int   mode,
+            const off_t offset,
+            const off_t len)
+  {
+    int rv;
+
+#ifdef __linux__
+    rv = ::fallocate(fd,mode,offset,len);
+#elif _XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L
+    rv = (mode ?
+          (errno=EOPNOTSUPP,-1) :
+          (::posix_fallocate(fd,offset,len)));
+#else
+    rv = (errno=EOPNOTSUPP,-1);
+#endif
+
+    return rv;
+  }
+}