From 0a1b735eed4e41f88b4e08af4fb1db99e08edf57 Mon Sep 17 00:00:00 2001
From: Edgar Gabriel <gabriel@cs.uh.edu>
Date: Thu, 7 Jan 2016 08:29:17 -0600
Subject: [PATCH] use the actual preadv and pwritev functions if available.
 That's what the fbtl interfaces have been designed for.

---
 ompi/mca/fbtl/posix/configure.m4         | 3 +++
 ompi/mca/fbtl/posix/fbtl_posix_preadv.c  | 7 +++++++
 ompi/mca/fbtl/posix/fbtl_posix_pwritev.c | 8 ++++++++
 3 files changed, 18 insertions(+)

diff --git a/ompi/mca/fbtl/posix/configure.m4 b/ompi/mca/fbtl/posix/configure.m4
index 8a6d548ea5..a03bd1a6f8 100644
--- a/ompi/mca/fbtl/posix/configure.m4
+++ b/ompi/mca/fbtl/posix/configure.m4
@@ -32,6 +32,9 @@ AC_DEFUN([MCA_ompi_fbtl_posix_CONFIG],[
                                     [aio_write], [rt],
                                     [fbtl_posix_happy="yes"])])
 
+    AC_CHECK_FUNCS([pwritev],[],[])
+    AC_CHECK_FUNCS([preadv],[],[])
+
     AS_IF([test "$fbtl_posix_happy" = "yes"],
           [$1],
           [$2])
diff --git a/ompi/mca/fbtl/posix/fbtl_posix_preadv.c b/ompi/mca/fbtl/posix/fbtl_posix_preadv.c
index ceb8b1d984..27dc589ee0 100644
--- a/ompi/mca/fbtl/posix/fbtl_posix_preadv.c
+++ b/ompi/mca/fbtl/posix/fbtl_posix_preadv.c
@@ -80,6 +80,12 @@ ssize_t mca_fbtl_posix_preadv (mca_io_ompio_file_t *fh )
 	    }
 	}
 
+#if defined(HAVE_PREADV)
+	ret_code = preadv (fh->fd, iov, iov_count, iov_offset);
+	if ( 0 < ret_code ) {
+	    bytes_read+=ret_code;
+	}
+#else
 	if (-1 == lseek (fh->fd, iov_offset, SEEK_SET)) {
             opal_output(1, "lseek:%s", strerror(errno));
             free(iov);
@@ -89,6 +95,7 @@ ssize_t mca_fbtl_posix_preadv (mca_io_ompio_file_t *fh )
 	if ( 0 < ret_code ) {
 	    bytes_read+=ret_code;
 	}
+#endif
 	else if ( ret_code == -1 ) {
             opal_output(1, "readv:%s", strerror(errno));
             free(iov);
diff --git a/ompi/mca/fbtl/posix/fbtl_posix_pwritev.c b/ompi/mca/fbtl/posix/fbtl_posix_pwritev.c
index 5208716d11..fbf69489ff 100644
--- a/ompi/mca/fbtl/posix/fbtl_posix_pwritev.c
+++ b/ompi/mca/fbtl/posix/fbtl_posix_pwritev.c
@@ -93,6 +93,13 @@ ssize_t  mca_fbtl_posix_pwritev(mca_io_ompio_file_t *fh )
 	  }
 
 	*/
+#if defined (HAVE_PWRITEV) 
+	ret_code = pwritev (fh->fd, iov, iov_count, iov_offset);
+	if ( 0 < ret_code ) {
+	    bytes_written += ret_code;
+	}
+
+#else
 	if (-1 == lseek (fh->fd, iov_offset, SEEK_SET)) {
 	    opal_output(1, "lseek:%s", strerror(errno));
             free(iov);
@@ -102,6 +109,7 @@ ssize_t  mca_fbtl_posix_pwritev(mca_io_ompio_file_t *fh )
 	if ( 0 < ret_code ) {
 	    bytes_written += ret_code;
 	}
+#endif
 	else if (-1 == ret_code ) {
 	    opal_output(1, "writev:%s", strerror(errno));
             free (iov);