[gparted] Update parsing of btrfs filesystem show for multi-device membership (#733601)

[Curtis Gedak <gedakc src gnome org>]

commit a4f761e290a32b7dcb43bd4cf3b9da232b9157e5
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Wed Jul 23 11:26:11 2014 +0100

    Update parsing of btrfs filesystem show for multi-device membership (#733601)
    
    This patch changes the reading of the btrfs multi-device membership to
    resolve issue 1/2 by ignoring the exit status from the 'btrfs filesystem
    show' command and relying on parsing the required information to
    determine success or failure.
    
    Bug #733601 - Btrfs: Warnings and missing label with btrfs-progs 3.12
                  and 3.14

 src/btrfs.cc |   46 ++++++++++++++++++++++------------------------
 1 files changed, 22 insertions(+), 24 deletions(-)
---
diff --git a/src/btrfs.cc b/src/btrfs.cc
index 7df2a2a..ba27f9c 100644
--- a/src/btrfs.cc
+++ b/src/btrfs.cc
@@ -463,36 +463,35 @@ const BTRFS_Device & btrfs::get_cache_entry( const Glib::ustring & path )
        if ( bd_iter != btrfs_device_cache .end() )
                return bd_iter ->second ;
 
-       int exit_status ;
        Glib::ustring output, error ;
        std::vector<int> devid_list ;
        std::vector<Glib::ustring> path_list ;
        if ( btrfs_found )
-               exit_status = Utils::execute_command( "btrfs filesystem show " + path, output, error, true ) ;
+               Utils::execute_command( "btrfs filesystem show " + path, output, error, true ) ;
        else
-               exit_status = Utils::execute_command( "btrfs-show " + path, output, error, true ) ;
-       if ( ! exit_status )
+               Utils::execute_command( "btrfs-show " + path, output, error, true ) ;
+       //In many cases the exit status doesn't reflect valid output or an error condition
+       //  so rely on parsing the output to determine success.
+
+       //Extract devid and path for each device from output like this:
+       //  Label: none  uuid: 36eb51a2-2927-4c92-820f-b2f0b5cdae50
+       //          Total devices 2 FS bytes used 156.00KB
+       //          devid    2 size 2.00GB used 512.00MB path /dev/sdb2
+       //          devid    1 size 2.00GB used 240.75MB path /dev/sdb1
+       Glib::ustring::size_type offset = 0 ;
+       Glib::ustring::size_type index ;
+       while ( ( index = output .find( "devid ", offset ) ) != Glib::ustring::npos )
        {
-               //Extract devid and path for each device from output like this:
-               //  Label: none  uuid: 36eb51a2-2927-4c92-820f-b2f0b5cdae50
-               //          Total devices 2 FS bytes used 156.00KB
-               //          devid    2 size 2.00GB used 512.00MB path /dev/sdb2
-               //          devid    1 size 2.00GB used 240.75MB path /dev/sdb1
-               Glib::ustring::size_type offset = 0 ;
-               Glib::ustring::size_type index ;
-               while ( ( index = output .find( "devid ", offset ) ) != Glib::ustring::npos )
+               int devid = -1 ;
+               sscanf( output .substr( index ) .c_str(), "devid %d", &devid ) ;
+               Glib::ustring devid_path = Utils::regexp_label( output .substr( index ),
+                                                               "devid .* path (/dev/[[:graph:]]+)" ) ;
+               if ( devid > -1 && ! devid_path .empty() )
                {
-                       int devid = -1 ;
-                       sscanf( output .substr( index ) .c_str(), "devid %d", &devid ) ;
-                       Glib::ustring devid_path = Utils::regexp_label( output .substr( index ),
-                                                                       "devid .* path (/dev/[[:graph:]]+)" ) 
;
-                       if ( devid > -1 && ! devid_path .empty() )
-                       {
-                               devid_list .push_back( devid ) ;
-                               path_list .push_back( devid_path ) ;
-                       }
-                       offset = index + 5 ;  //Next find starts immediately after current "devid"
+                       devid_list .push_back( devid ) ;
+                       path_list .push_back( devid_path ) ;
                }
+               offset = index + 5 ;  //Next find starts immediately after current "devid"
        }
        //Add cache entries for all found devices
        for ( unsigned int i = 0 ; i < devid_list .size() ; i ++ )
@@ -507,8 +506,7 @@ const BTRFS_Device & btrfs::get_cache_entry( const Glib::ustring & path )
        if ( bd_iter != btrfs_device_cache .end() )
                return bd_iter ->second ;
 
-       //If "btrfs filesystem show" / "btrfs-show" commands not found, returned non-zero
-       //  exit status or failed to parse information return an "unknown" record
+       //If for any reason we fail to parse the information return an "unknown" record
        static BTRFS_Device btrfs_dev = { -1, } ;
        return btrfs_dev ;
 }