iohelper: Don't report errors on special FDs

Some FDs may not implement fdatasync() functionality,
e.g.  pipes. In that case EINVAL or EROFS is returned.
We don't want to fail then nor report any error.
Reported-by: NChristophe Fergeau <cfergeau@redhat.com>
(cherry picked from commit 46325e51)

src/util/iohelper.c

@@ -181,9 +181,12 @@ runIO(const char *path, int fd, int oflags, unsigned long long length)
 
     /* Ensure all data is written */
     if (fdatasync(fdout) < 0) {
+        if (errno != EINVAL && errno != EROFS) {
+            /* fdatasync() may fail on some special FDs, e.g. pipes */
             virReportSystemError(errno, _("unable to fsync %s"), fdoutname);
             goto cleanup;
         }
+    }
 
     ret = 0;