Simplify pg_upgrade executable checks

The attached patch simplifies pg_upgrade's checking of executables, per
suggestion from Robert Haas.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +
diff --git a/contrib/pg_upgrade/exec.c b/contrib/pg_upgrade/exec.c
index cce40e4..3ad9dbb 100644
*** a/contrib/pg_upgrade/exec.c
--- b/contrib/pg_upgrade/exec.c
***************
*** 15,22 ****

  static void check_data_dir(const char *pg_data);
  static void check_bin_dir(ClusterInfo *cluster);
! static int    check_exec(const char *dir, const char *cmdName);
! static const char *validate_exec(const char *path);


  /*
--- 15,21 ----

  static void check_data_dir(const char *pg_data);
  static void check_bin_dir(ClusterInfo *cluster);
! static void    validate_exec(const char *dir, const char *cmdName);


  /*
*************** check_data_dir(const char *pg_data)
*** 160,217 ****
  static void
  check_bin_dir(ClusterInfo *cluster)
  {
!     check_exec(cluster->bindir, "postgres");
!     check_exec(cluster->bindir, "pg_ctl");
!     check_exec(cluster->bindir, "pg_resetxlog");
      if (cluster == &new_cluster)
      {
          /* these are only needed in the new cluster */
!         check_exec(cluster->bindir, "pg_config");
!         check_exec(cluster->bindir, "psql");
!         check_exec(cluster->bindir, "pg_dumpall");
      }
  }


  /*
-  * check_exec()
-  *
-  *    Checks whether either of the two command names (cmdName and alternative)
-  *    appears to be an executable (in the given directory).  If dir/cmdName is
-  *    an executable, this function returns 1. If dir/alternative is an
-  *    executable, this function returns 2.  If neither of the given names is
-  *    a valid executable, this function returns 0 to indicated failure.
-  */
- static int
- check_exec(const char *dir, const char *cmdName)
- {
-     char        path[MAXPGPATH];
-     const char *errMsg;
-
-     snprintf(path, sizeof(path), "%s/%s", dir, cmdName);
-
-     if ((errMsg = validate_exec(path)) == NULL)
-         return 1;                /* 1 -> first alternative OK */
-     else
-         pg_log(PG_FATAL, "check for %s failed - %s\n", cmdName, errMsg);
-
-     return 0;                    /* 0 -> neither alternative is acceptable */
- }
-
-
- /*
   * validate_exec()
   *
   * validate "path" as an executable file
-  * returns 0 if the file is found and no error is encountered.
-  *          -1 if the regular file "path" does not exist or cannot be executed.
-  *          -2 if the file is otherwise valid but cannot be read.
   */
! static const char *
! validate_exec(const char *path)
  {
      struct stat buf;

  #ifdef WIN32
      /* Win32 requires a .exe suffix for stat() */
      char        path_exe[MAXPGPATH + sizeof(EXE_EXT) - 1];
--- 159,190 ----
  static void
  check_bin_dir(ClusterInfo *cluster)
  {
!     validate_exec(cluster->bindir, "postgres");
!     validate_exec(cluster->bindir, "pg_ctl");
!     validate_exec(cluster->bindir, "pg_resetxlog");
      if (cluster == &new_cluster)
      {
          /* these are only needed in the new cluster */
!         validate_exec(cluster->bindir, "pg_config");
!         validate_exec(cluster->bindir, "psql");
!         validate_exec(cluster->bindir, "pg_dumpall");
      }
  }


  /*
   * validate_exec()
   *
   * validate "path" as an executable file
   */
! static void
! validate_exec(const char *dir, const char *cmdName)
  {
+     char        path[MAXPGPATH];
      struct stat buf;

+     snprintf(path, sizeof(path), "%s/%s", dir, cmdName);
+
  #ifdef WIN32
      /* Win32 requires a .exe suffix for stat() */
      char        path_exe[MAXPGPATH + sizeof(EXE_EXT) - 1];
*************** validate_exec(const char *path)
*** 229,238 ****
       * Ensure that the file exists and is a regular file.
       */
      if (stat(path, &buf) < 0)
!         return getErrorText(errno);

      if (!S_ISREG(buf.st_mode))
!         return "not an executable file";

      /*
       * Ensure that the file is both executable and readable (required for
--- 202,213 ----
       * Ensure that the file exists and is a regular file.
       */
      if (stat(path, &buf) < 0)
!         pg_log(PG_FATAL, "check for %s failed - %s\n",
!                cmdName, getErrorText(errno));

      if (!S_ISREG(buf.st_mode))
!         pg_log(PG_FATAL, "check for %s failed - not an executable file\n",
!                cmdName);

      /*
       * Ensure that the file is both executable and readable (required for
*************** validate_exec(const char *path)
*** 240,254 ****
       */
  #ifndef WIN32
      if (access(path, R_OK) != 0)
-         return "can't read file (permission denied)";
-     if (access(path, X_OK) != 0)
-         return "can't execute (permission denied)";
-     return NULL;
  #else
      if ((buf.st_mode & S_IRUSR) == 0)
!         return "can't read file (permission denied)";
      if ((buf.st_mode & S_IXUSR) == 0)
-         return "can't execute (permission denied)";
-     return NULL;
  #endif
  }
--- 215,231 ----
       */
  #ifndef WIN32
      if (access(path, R_OK) != 0)
  #else
      if ((buf.st_mode & S_IRUSR) == 0)
! #endif
!         pg_log(PG_FATAL, "check for %s failed - cannot read file (permission denied)\n",
!                cmdName);
!
! #ifndef WIN32
!     if (access(path, X_OK) != 0)
! #else
      if ((buf.st_mode & S_IXUSR) == 0)
  #endif
+         pg_log(PG_FATAL, "check for %s failed - cannot execute (permission denied)\n",
+                cmdName);
  }