Implement shell style exit status decoding (#754684)

Command exit status is a 1 byte value between 0 and 255. [1][2]  However
at the Unix API level the value is encoded as documented in the
waitpid(2) manual page.  This is true for the Glib API too. [3]  This is
why, for example, the comment in ext2::check_repair() reported receiving
undocumented exit status 256.  It was actually receiving exit status 1
encoded as per the waitpid(2) method.

Add shell style exit status decoding [2] to execution of all external
commands.   Return value from Utils::execute_command() and
FileSystem::execute_command() functions are now:
    0 - 125 - Exit status from the command
    126     - Error executing the command
    127     - Command not found
    128+N   - Command terminated by signal N
    255     - Unexpected waitpid(2) condition
Also adjust checking of the returned statuses as necessary.

[1] Advanced Bash-Scripting Guide: Appendix D. Exit Codes With Special
    Meanings
    http://www.linuxtopia.org/online_books/advanced_bash_scripting_guide/exitcodes.html

[2] Quote from the bash(1) manual page:

        EXIT STATUS
            ... Exit statuses fall between 0 and 255, though as
            explained below, the shell may use values above 125
            specially.  ...

            ... When a command terminates on a fatal signal N, bash uses
            the value of 128+N as the exit status.

            If a command is not found, the child process created to
            execute it returns a status of 127.  If a command is found
            but is not executable, the return status is 126.

[3] Quote from the Glib Reference Manual, Spawning Processes section,
    for function g_spawn_check_exit_status():
    https://developer.gnome.org/glib/stable/glib-Spawning-Processes.html#g-spawn-check-exit-status

        The g_spawn_sync() and g_child_watch_add() family of APIs return
        an exit status for subprocesses encoded in a platform-specific
        way.  On Unix, this is guaranteed to be in the same format
        waitpid() returns, ...

Bug 754684 - Updates to FileSystem:: and Utils::execute_command()
             functions

include/Utils.h

@@ -190,6 +190,8 @@ public:
 				    Glib::ustring & output,
 				    Glib::ustring & error,
 				    bool use_C_locale = false ) ;
+	static int get_failure_status( Glib::SpawnError & e );
+	static int decode_wait_status( int wait_status );
 	static Glib::ustring regexp_label( const Glib::ustring & text
 	                                 , const Glib::ustring & pattern
 	                                 ) ;

src/FileSystem.cc

@@ -54,7 +54,7 @@ const Glib::ustring FileSystem::get_generic_text( CUSTOM_TEXT ttype, int index )
 
 void FileSystem::store_exit_status( GPid pid, int status )
 {
-	exit_status = status;
+	exit_status = Utils::decode_wait_status( status );
 	running = false;
 	if (pipecount == 0) // pipes finished first
 		Gtk::Main::quit();
@@ -102,7 +102,7 @@ int FileSystem::execute_command( const Glib::ustring & command, OperationDetail
 		std::cerr << e.what() << std::endl;
 		operationdetail.get_last_child().add_child(
 			OperationDetail( e.what(), STATUS_ERROR, FONT_ITALIC ) );
-		return 1;
+		return Utils::get_failure_status( e );
 	}
 	fcntl( out, F_SETFL, O_NONBLOCK );
 	fcntl( err, F_SETFL, O_NONBLOCK );

src/Utils.cc

@@ -33,6 +33,8 @@
 #include <sys/statvfs.h>
 #include <gtkmm/main.h>
 #include <fcntl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
 
 namespace GParted
 {
@@ -529,7 +531,7 @@ public:
 
 void CommandStatus::store_exit_status( GPid pid, int status )
 {
-	exit_status = status;
+	exit_status = Utils::decode_wait_status( status );
 	running = false;
 	if (pipecount == 0) // pipes finished first
 	{
@@ -596,7 +598,7 @@ int Utils::execute_command( const Glib::ustring & command,
 			&err );
 	} catch (Glib::SpawnError &e) {
 		std::cerr << e.what() << std::endl;
-		return 1;
+		return Utils::get_failure_status( e );
 	}
 	fcntl( out, F_SETFL, O_NONBLOCK );
 	fcntl( err, F_SETFL, O_NONBLOCK );
@@ -625,6 +627,34 @@ int Utils::execute_command( const Glib::ustring & command,
 	return status.exit_status;
 }
 
+// Return shell style exit status when failing to execute a command.  127 for command not
+// found and 126 otherwise.
+// NOTE:
+// Together get_failure_status() and decode_wait_status() provide complete shell style
+// exit status handling.  See bash(1) manual page, EXIT STATUS section for details.
+int Utils::get_failure_status( Glib::SpawnError & e )
+{
+	if ( e.code() == Glib::SpawnError::NOENT )
+		return 127;
+	return 126;
+}
+
+// Return shell style decoding of waitpid(2) encoded exit statuses.  Return command exit
+// status or 128 + signal number when terminated by a signal.
+int Utils::decode_wait_status( int wait_status )
+{
+	if ( WIFEXITED( wait_status ) )
+		return WEXITSTATUS( wait_status );
+	else if ( WIFSIGNALED( wait_status ) )
+		return 128 + WTERMSIG( wait_status );
+
+	// Other cases of WIFSTOPPED() and WIFCONTINUED() occur when the process is
+	// stopped or resumed by signals.  Should be impossible as this function is only
+	// called after the process has exited.
+	std::cerr << "Unexpected wait status " << wait_status << std::endl;
+	return 255;
+}
+
 Glib::ustring Utils::regexp_label( const Glib::ustring & text
                                  , const Glib::ustring & pattern
                                  )

src/btrfs.cc

@@ -356,8 +356,8 @@ bool btrfs::resize( const Partition & partition_new, OperationDetail & operation
 			//  but not ignoring them will cause resizing to the
 			//  same size as part of check operation to fail.
 			resize_succeeded = (    exit_status == 0
-			                     || (   btrfs_found && exit_status == 30<<8 )
+			                     || (   btrfs_found && exit_status == 30 )
-			                     || ( ! btrfs_found && exit_status ==  1<<8 )
+			                     || ( ! btrfs_found && exit_status ==  1 )
 			                   ) ;
 		}
 		set_status( operationdetail, resize_succeeded );

src/ext2.cc

@@ -240,10 +240,7 @@ bool ext2::check_repair( const Partition & partition, OperationDetail & operatio
 {
 	exit_status = execute_command( fsck_cmd + " -f -y -v -C 0 " + partition.get_path(), operationdetail,
 	                               EXEC_CANCEL_SAFE );
-
+	bool success = ( exit_status == 0 || exit_status == 1 || exit_status == 2 );
-	//exitstatus 256 isn't documented, but it's returned when the 'FILE SYSTEM IS MODIFIED'
-	//this is quite normal (especially after a copy) so we let the function return true...
-	bool success = ( exit_status == 0 || exit_status == 1 || exit_status == 2 || exit_status == 256 );
 	set_status( operationdetail, success );
 	return success;
 }

src/fat16.cc

@@ -128,7 +128,7 @@ FS fat16::get_filesystem_support()
 void fat16::set_used_sectors( Partition & partition ) 
 {
 	exit_status = Utils::execute_command( check_cmd + " -n -v " + partition .get_path(), output, error, true ) ;
-	if ( exit_status == 0 || exit_status == 1 || exit_status == 256 )
+	if ( exit_status == 0 || exit_status == 1 )
 	{
 		//total file system size in logical sectors
 		index = output .rfind( "\n", output .find( "sectors total" ) ) +1 ;
@@ -239,7 +239,7 @@ bool fat16::check_repair( const Partition & partition, OperationDetail & operati
 {
 	exit_status = execute_command( check_cmd + " -a -w -v " + partition .get_path(), operationdetail,
 	                               EXEC_CANCEL_SAFE );
-	bool success = ( exit_status == 0 || exit_status == 1 || exit_status == 256 );
+	bool success = ( exit_status == 0 || exit_status == 1 );
 	set_status( operationdetail, success );
 	return success;
 }

src/ntfs.cc

@@ -121,7 +121,7 @@ void ntfs::set_used_sectors( Partition & partition )
 {
 	exit_status = Utils::execute_command(
 		"ntfsresize --info --force --no-progress-bar " + partition .get_path(), output, error, true ) ;
-	if ( exit_status == 0 || exit_status == 1<<8 )
+	if ( exit_status == 0 || exit_status == 1 )
 	{
 		index = output .find( "Current volume size:" ) ;
 		if ( index >= output .length() ||

src/reiserfs.cc

@@ -176,7 +176,12 @@ bool reiserfs::resize( const Partition & partition_new, OperationDetail & operat
 	Glib::ustring cmd = "sh -c 'echo y | resize_reiserfs" + size + " " + partition_new .get_path() + "'" ;
 
 	exit_status = execute_command( cmd, operationdetail ) ;
-	bool success = ( exit_status == 0 || exit_status == 256 );
+	// NOTE: Neither resize_reiserfs manual page nor the following commit, which first
+	// added this check, indicate why exit status 1 also indicates success.  Commit
+	// from 2006-05-23:
+	//     7bb7e8a84f164cd913384509a6adc3739a9d8b78
+	//     Use ped_device_read and ped_device_write instead of 'dd' to copy
+	bool success = ( exit_status == 0 || exit_status == 1 );
 	set_status( operationdetail, success );
 	return success;
 }
@@ -185,7 +190,7 @@ bool reiserfs::check_repair( const Partition & partition, OperationDetail & oper
 {
 	exit_status = execute_command( "reiserfsck --yes --fix-fixable --quiet " + partition.get_path(),
 	                               operationdetail, EXEC_CANCEL_SAFE );
-	bool success = ( exit_status == 0 || exit_status == 1 || exit_status == 256 );
+	bool success = ( exit_status == 0 || exit_status == 1 );
 	set_status( operationdetail, success );
 	return success;
 }