[Server] Implement the Flush() method.

src/XrdOss/XrdOssApi.cc

@@ -1028,6 +1028,28 @@ int XrdOssFile::Fchmod(mode_t Mode)
     return (fchmod(fd, Mode) ? -errno : XrdOssOK);
 }
 
+/******************************************************************************/
+/*                                 F l u s h                                  */
+/******************************************************************************/
+
+/*
+  Function: Flush file pages from the filesyste cacheÂ.
+
+  Output:   Returns XrdOssOK upon success and -errno upon failure.
+*/
+
+void XrdOssFile::Flush()
+{
+// This actually only works in Linux so we punt otherwise
+//
+#if defined(__linux__)
+   if (fd>= 0)
+      {fdatasync(fd);
+       posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED);
+      }
+#endif
+}
+
 /******************************************************************************/
 /*                                 F s t a t                                  */
 /******************************************************************************/

src/XrdOss/XrdOssApi.hh

@@ -92,6 +92,7 @@ virtual int     Close(long long *retsz=0);
 virtual int     Open(const char *, int, mode_t, XrdOucEnv &);
 
 int     Fchmod(mode_t mode);
+void    Flush();
 int     Fstat(struct stat *);
 int     Fsync();
 int     Fsync(XrdSfsAio *aiop);