Confirm backward compatibility for PIO reads on non-parallel files (#966)

Add ability for netcdf file reading to fall back to regular netcdf if a file is initially opened (for instance with hdf5 reading) and fails to open properly.

For some versions of the PIO library (<2.5.10), attempting a parallel read with filetype netcdf4 (hdf5) of a file which does not support parallel reads fails. The expected behaviour (which is fixed in latest PIO versions) is to fall back to a serial read. The change ensures support for older PIO versions.

Author: anton-seaice

cicecore/cicedyn/infrastructure/io/io_pio2/ice_pio.F90

@@ -236,8 +236,14 @@ subroutine ice_pio_init(mode, filename, File, clobber, fformat, &
                write(nu_diag,*) subname//' opening file for reading '//trim(filename)
             endif
             status = pio_openfile(ice_pio_subsystem, File, pio_iotype, trim(filename), pio_nowrite)
-            call ice_pio_check( status, subname//' ERROR: Failed to open file '//trim(filename), &
-             file=__FILE__,line=__LINE__)
+            if (status /= PIO_NOERR) then
+               if (my_task == master_task) then
+                  write(nu_diag,*) subname//' opening '//trim(filename)//' as type '//trim(fformat)//' failed, retrying as type cdf1'
+               endif
+               status = pio_openfile(ice_pio_subsystem, File, PIO_IOTYPE_NETCDF, trim(filename), pio_nowrite)
+               call ice_pio_check( status, subname//' ERROR: Failed to open file '//trim(filename), &
+               file=__FILE__,line=__LINE__)
+            endif
          else
             if(my_task==master_task) then
                write(nu_diag,*) subname//' ERROR: file not found '//trim(filename)

cicecore/cicedyn/infrastructure/io/io_pio2/ice_restart.F90

@@ -78,13 +78,8 @@ subroutine init_restart_read(ice_ic)
       end if
 
       File%fh=-1
-! tcraig, including fformat here causes some problems when restart_format=hdf5
-!         and reading non hdf5 files with spack built PIO.  Excluding the fformat
-!         argument here defaults the PIO format to cdf1 which then reads
-!         any netcdf format file fine.
       call ice_pio_init(mode='read', filename=trim(filename), File=File, &
-!          fformat=trim(restart_format), rearr=trim(restart_rearranger), &
-                                         rearr=trim(restart_rearranger), &
+           fformat=trim(restart_format), rearr=trim(restart_rearranger), &
            iotasks=restart_iotasks, root=restart_root, stride=restart_stride, &
            debug=first_call)