Be a bit more consistent about comparing to zero

* src/buffer.c (xclose, archive_is_dev, close_archive)
(write_fatal_details, init_volume_number)
(closeout_volume_number, new_volume, try_new_volume):
* src/checkpoint.c (format_checkpoint_string):
* src/compare.c (process_rawdata, diff_file, diff_dumpdir):
* src/create.c (create_archive, restore_parent_fd, dump_file0):
* src/delete.c (delete_archive_members):
* src/exclist.c (cvs_addfn):
* src/extract.c (set_mode, mark_after_links, delay_set_stat)
(repair_delayed_set_stat, make_directories, file_newer_p)
(maybe_recoverable, apply_nonancestor_delayed_set_stat)
(extract_dir, open_output_file, find_delayed_link_source)
(create_placeholder_file, extract_symlink, extract_node)
(extract_fifo, apply_delayed_link):
* src/incremen.c (update_parent_directory, scan_directory)
(read_obstack, read_incr_db_2, write_directory_file)
(try_purge_directory):
* src/map.c (map_read):
* src/misc.c (maybe_backup_file, undo_last_backup, chdir_do)
(tar_savedir):
* src/names.c (handle_file_selection_option, add_file_id)
(handle_option, read_next_name, add_hierarchy_to_namelist)
(collect_and_sort_names):
* src/system.c (run_decompress_program, dec_to_env, time_to_env)
(oct_to_env, str_to_env, chr_to_env, sys_exec_setmtime_script):
* src/tar.c (get_date_or_file, parse_default_options)
(decode_options, main):
* src/unlink.c (flush_deferred_unlinks):
* src/update.c (append_file):
* src/xattrs.c (xattrs__acls_set, xattrs_xattrs_set):
Prefer < 0 when looking at syscalls; prefer != 0 to nothing
when testing an integer in a boolean context.
This is for style, not substance; for example, it’s easier
to read ‘if (wordsplit (...) != WRDSE_OK) ...’ than
‘if (wordsplit (...)) ...’ if you don’t already know that
wordsplit returns an enum rather than bool.
* src/names.c (add_file_id, read_next_name, regex_usage_warning):
* src/transform.c (parse_xform_flags):
Return bool not int, possibly inverting sense so that true means OK.
All callers changed.
* src/tar.c (main): Report errno info if stdopen fails.

src/create.c

@@ -1346,7 +1346,7 @@ create_archive (void)
 			      break;
 			    }
 			  st.fd = fd;
-			  if (fstat (fd, &st.stat) != 0)
+			  if (fstat (fd, &st.stat) < 0)
 			    {
 			      file_removed_diag (p->name, !p->parent,
 						 stat_diag);
@@ -1555,9 +1555,9 @@ restore_parent_fd (struct tar_stat_info const *st)
 
       if (parentfd < 0)
 	parentfd = - errno;
-      else if (! (fstat (parentfd, &parentstat) == 0
-		  && parent->stat.st_ino == parentstat.st_ino
-		  && parent->stat.st_dev == parentstat.st_dev))
+      else if (fstat (parentfd, &parentstat) < 0
+	       || parent->stat.st_ino != parentstat.st_ino
+	       || parent->stat.st_dev != parentstat.st_dev)
 	{
 	  close (parentfd);
 	  parentfd = IMPOSTOR_ERRNO;
@@ -1569,12 +1569,12 @@ restore_parent_fd (struct tar_stat_info const *st)
 			       open_searchdir_flags);
 	  if (0 <= origfd)
 	    {
-	      if (fstat (parentfd, &parentstat) == 0
-		  && parent->stat.st_ino == parentstat.st_ino
-		  && parent->stat.st_dev == parentstat.st_dev)
-		parentfd = origfd;
-	      else
+	      if (fstat (parentfd, &parentstat) < 0
+		  || parent->stat.st_ino != parentstat.st_ino
+		  || parent->stat.st_dev != parentstat.st_dev)
 		close (origfd);
+	      else
+		parentfd = origfd;
 	    }
 	}
 
@@ -1619,7 +1619,7 @@ dump_file0 (struct tar_stat_info *st, char const *name, char const *p)
       errno = - parentfd;
       diag = open_diag;
     }
-  else if (fstatat (parentfd, name, &st->stat, fstatat_flags) != 0)
+  else if (fstatat (parentfd, name, &st->stat, fstatat_flags) < 0)
     diag = stat_diag;
   else if (file_dumpable_p (&st->stat))
     {
@@ -1629,7 +1629,7 @@ dump_file0 (struct tar_stat_info *st, char const *name, char const *p)
       else
 	{
 	  st->fd = fd;
-	  if (fstat (fd, &st->stat) != 0)
+	  if (fstat (fd, &st->stat) < 0)
 	    diag = stat_diag;
 	}
     }
@@ -1804,7 +1804,7 @@ dump_file0 (struct tar_stat_info *st, char const *name, char const *p)
 	    }
 	  else if (atime_preserve_option == replace_atime_preserve
 		   && timespec_cmp (st->atime, get_stat_atime (&st2)) != 0
-		   && set_file_atime (fd, parentfd, name, st->atime) != 0)
+		   && set_file_atime (fd, parentfd, name, st->atime) < 0)
 	    utime_error (p);
 	}