check for avialablity of pwrite

We can test at configure-time if pread/pwrite is available.
XOPEN_SOURCE set low enough will not provide this feature, for example
(as is the case with --enable-strict).
Signed-off-by: Ken Raffenetti <raffenet@mcs.anl.gov>

src/mpi/romio/adio/common/utils.c

@@ -105,6 +105,35 @@ int ADIOI_Type_create_hindexed_x(int count,
     return ret;
 }
 
+/* some systems do not have pread/pwrite, or requrie XOPEN_SOURCE set higher
+ * than we would like.  see #1973 */
+#if (HAVE_DECL_PWRITE == 0)
+
+#include <sys/types.h>
+#include <unistd.h>
+
+ssize_t pread(int fd, void *buf, size_t count, off_t offset);
+ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
+
+ssize_t pread(int fd, void *buf, size_t count, off_t offset) {
+    off_t lseek_ret;
+
+    lseek_ret = lseek(fd, offset, SEEK_SET);
+    if (lseek_ret == -1)
+	return lseek_ret;
+    return (read(fd, buf, count));
+}
+
+ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset) {
+    off_t lseek_ret;
+
+    lseek_ret = lseek(fd, offset, SEEK_SET);
+    if (lseek_ret == -1)
+	return lseek_ret;
+    return (write(fd, buf, count));
+}
+#endif
+
 /*
  * vim: ts=8 sts=4 sw=4 noexpandtab
  */

src/mpi/romio/adio/include/adioi.h

@@ -1044,3 +1044,10 @@ void *ADIOI_IO_Thread_Func(void *vptr_args);
 
 #endif
 
+
+#if (HAVE_DECL_PWRITE == 0)
+#include <sys/types.h>
+#include <unistd.h>
+ssize_t pread(int fd, void *buf, size_t count, off_t offset);
+ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
+#endif

src/mpi/romio/configure.ac

@@ -1414,6 +1414,14 @@ if test "$ac_cv_header_unistd_h" = "yes" ; then
     fi
 fi
 
+# pread and pwrite are useful to ROMIO: if implemented well, they help us avoid
+# an extra system call.  But --enable-strict or CFLAGS="--std=c99" does not
+# expose this feature.  If we define XOPEN_SOURCE in ROMIO, we cause headaches
+# for some versions of lustre, quota.h, and caddr_t.  see if we need to provide
+# our own pread/pwrite
+
+AC_CHECK_DECLS([pwrite])
+
 
 ####################################################################
 # We're about to mess with CC etc.  No more feature tests past here,