Use POSIX stat to check if restart dir exists

Using inquire() to check for directory existence is not possible, since
at least one compiler (Intel) does not consider directories to be files.

The inquire call is replaced with a C interface to the POSIX stat()
function.  We do not fully emulate the behavior of stat, but we use its
return value to determine existence of directories.  This provides a
more reliable method for identifying the existence of the directory.

This should resolve many of the observed problems with RESTART creation
in coupled runs.

src/framework/MOM_get_input.F90

@@ -11,7 +11,7 @@ module MOM_get_input
 use MOM_file_parser, only : open_param_file, param_file_type
 use MOM_io, only : file_exists, close_file, slasher, ensembler
 use MOM_io, only : open_namelist_file, check_nml_error
-use posix, only : mkdir
+use posix, only : mkdir, stat, stat_buf
 
 implicit none ; private
 
@@ -55,6 +55,8 @@ subroutine get_MOM_input(param_file, dirs, check_params, default_input_filename,
   character(len=240) :: output_dir
   integer :: unit, io, ierr, valid_param_files
 
+  type(stat_buf) :: buf
+
   namelist /MOM_input_nml/ output_directory, input_filename, parameter_filename, &
                            restart_input_dir, restart_output_dir
 
@@ -97,7 +99,7 @@ subroutine get_MOM_input(param_file, dirs, check_params, default_input_filename,
 
     ! Create the RESTART directory if absent
     if (is_root_PE()) then
-      if (.not. file_exists(dirs%restart_output_dir)) then
+      if (stat(trim(dirs%restart_output_dir), buf) == -1) then
         ierr = mkdir(trim(dirs%restart_output_dir), int(o'700'))
         if (ierr == -1) &
           call MOM_error(FATAL, 'Restart directory could not be created.')

src/framework/posix.F90

@@ -13,6 +13,16 @@ module posix
 
 implicit none
 
+!> Container for file metadata from stat
+!!
+!! NOTE: This is currently just a placeholder containing fields, such as size,
+!! uid, mode, etc.  A readable Fortran type may be used in the future.
+type, bind(c) :: stat_buf
+  private
+  character(kind=c_char) :: state(SIZEOF_STAT_BUF)
+    !< Byte array containing file metadata
+end type stat_buf
+
 !> Container for the jump point buffer created by setjmp().
 !!
 !! The buffer typically contains the current register values, stack pointers,
@@ -67,6 +77,19 @@ function mkdir_posix(path, mode) result(rc) bind(c, name="mkdir")
       !< Function return code
   end function mkdir_posix
 
+  !> C interface to POSIX stat()
+  !! Users should use the Fortran-defined stat() function.
+  function stat_posix(path, buf) result(rc) bind(c, name="stat")
+    import :: c_char, stat_buf, c_int
+
+    character(kind=c_char), dimension(*), intent(in) :: path
+      !< Pathname of a POSIX file
+    type(stat_buf), intent(in) :: buf
+      !< Information describing the file if it exists
+    integer(kind=c_int) :: rc
+      !< Function return code
+  end function
+
   !> C interface to POSIX signal()
   !! Users should use the Fortran-defined signal() function.
   function signal_posix(sig, func) result(handle) bind(c, name="signal")
@@ -272,6 +295,27 @@ function mkdir(path, mode) result(rc)
   rc = int(rc_c)
 end function mkdir
 
+!> Get file status
+!!
+!! This obtains information about the named file and writes it to buf.
+!! If found, it returns zero.  Otherwise, it returns -1.
+function stat(path, buf) result(rc)
+  character(len=*), intent(in) :: path
+    !< Pathname of file to be inspected
+  type(stat_buf), intent(out) :: buf
+    !< Buffer containing information about the file if it exists
+    ! NOTE: Currently the contents of buf are not readable, but we could move
+    ! the contents into a readable Fortran type.
+  integer :: rc
+    !< Function return code
+
+  integer(kind=c_int) :: rc_c
+
+  rc_c = stat_posix(path//c_null_char, buf)
+
+  rc = int(rc_c)
+end function stat
+
 !> Create a signal handler `handle` to be called when `sig` is detected.
 !!
 !! If successful, the previous handler for `sig` is returned.  Otherwise,
@@ -391,6 +435,9 @@ function setjmp_missing(env) result(rc) bind(c)
   print '(a)', 'ERROR: setjmp() is not implemented in this build.'
   print '(a)', 'Recompile with autoconf or -DSETJMP_NAME=\"<symbol name>\".'
   error stop
+
+  ! NOTE: compilers may expect a return value, even if it is unreachable
+  rc = -1
 end function setjmp_missing
 
 !> Placeholder function for a missing or unconfigured longjmp
@@ -418,7 +465,7 @@ function sigsetjmp_missing(env, savesigs) result(rc) bind(c)
   print '(a)', 'Recompile with autoconf or -DSIGSETJMP_NAME=\"<symbol name>\".'
   error stop
 
-  ! NOTE: Compilers may expect a return value, even if it is unreachable
+  ! NOTE: compilers may expect a return value, even if it is unreachable
   rc = -1
 end function sigsetjmp_missing
 

src/framework/posix.h

@@ -1,6 +1,12 @@
 #ifndef MOM6_POSIX_H_
 #define MOM6_POSIX_H_
 
+! STAT_BUF_SIZE should be set to sizeof(stat).
+! The default value is based on glibc 2.28.
+#ifndef SIZEOF_STAT_BUF
+#define SIZEOF_STAT_BUF 144
+#endif
+
 ! JMP_BUF_SIZE should be set to sizeof(jmp_buf).
 ! If unset, then use a typical glibc value (25 long ints)
 #ifndef SIZEOF_JMP_BUF