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Display usage for multi-device btrfs file systems (#723842) 

Currently GParted fails to report the usage of a multi-device btrfs file
system if it is mounted or if the used space is larger than the size of
an individual member device.  When GParted does display usage figures it
also incorrectly reports the file system wide used figure against every
member device.

Mounted case:
    statvfs() provides an FS size which is larger than any individual
    device so is rejected.  See:
        GParted_Core::mounted_set_used_sectors()
            Utils::get_mounted_filesystem_usage()
            partition .set_sector_usage()

Unmounted case, FS used > device size:
    FS used figure is larger than any individual device so free space is
    calculated as a negative number and rejected.  See:
        btrfs::set_used_sectors()

Btrfs has a volume manager layer within the file system which allows it
to provide multiple levels of data redundancy, RAID levels, and use
multiple devices both of which can be changed while the file system is
mounted.  To achieve this btrfs has to allocate space at two different
level: (1) chunks of 256 MiB or more at the volume manager level; and
(2) extents at the file data level.
References:
*   Btrfs: Working with multiple devices
    https://lwn.net/Articles/577961/
*   Btrfs wiki: Glossary
    https://btrfs.wiki.kernel.org/index.php/Glossary

This makes the question of how much disk space is being used in an
individual device a complicated question to answer.  Further, the
current btrfs tools don't provide the required information.

Btrfs filesystem show only provides space usage information at the chunk
level per device.  At the file extent level only a single figure for the
whole file system is provided.  It also reports size of the data and
metadata being stored, not the larger figure of the amount of space
taken after redundancy is applied.  So it is impossible to answer the
question of how much disk space is being used in an individual device.
Example output:

    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

Fix by guesstimating the per device used figure as the fraction of the
file system wide extent usage based on chunk usage per device.
Calculation:
    ptn fs used = total fs used * devid used / sum devid used

Positives:
1) Per device used figure will correctly be between zero and allocated
   chunk size.

Known inaccuracies:
[for single and multi-device btrfs file systems]
1) Btrfs filesystem show reports file system wide file extent usage
   without considering redundancy applied to that data.  (By default
   btrfs stores two copies of metadata and one copy of data).
2) At minimum size when all data has been consolidated there will be a
   few partly filled chunks of 256 MiB or more for data and metadata of
   each storage profile (RAID level).
[for multi-device btrfs file systems only]
3) Data may be far from evenly distributed between the chunks on
   multiple devices.
4) Extents can be and are relocated to other devices within the file
   system when shrinking a device.

Bug #723842 - GParted resizes the wrong filesystem (does not pass the
              devid to btrfs filesystem resize)
This commit is contained in:
Mike Fleetwood 2014-03-29 21:12:01 +00:00 committed by Curtis Gedak
parent a086e115e5
commit 1712809e01
1 changed files with 105 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

123
src/btrfs.cc
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@ -113,7 +113,7 @@ FS btrfs::get_filesystem_support()
fs .move = GParted::FS::GPARTED ;
}
fs .online_read = FS::GPARTED ;
fs .online_read = FS::EXTERNAL ;
#ifdef ENABLE_ONLINE_RESIZE
if ( Utils::kernel_version_at_least( 3, 6, 0 ) )
{
@ -156,34 +156,121 @@ bool btrfs::check_repair( const Partition & partition, OperationDetail & operati
void btrfs::set_used_sectors( Partition & partition )
{
//Called when the file system is unmounted *and* when mounted.
//
// Btrfs has a volume manager layer within the file system which allows it to
// provide multiple levels of data redundancy, RAID levels, and use multiple
// devices both of which can be changed while the file system is mounted. To
// achieve this btrfs has to allocate space at two different levels: (1) chunks
// of 256 MiB or more at the volume manager level; and (2) extents at the file
// data level.
// References:
// * Btrfs: Working with multiple devices
// https://lwn.net/Articles/577961/
// * Btrfs wiki: Glossary
// https://btrfs.wiki.kernel.org/index.php/Glossary
//
// This makes the question of how much disk space is being used in an individual
// device a complicated question to answer. Further, the current btrfs tools
// don't provide the required information.
//
// Btrfs filesystem show only provides space usage information at the chunk level
// per device. At the file extent level only a single figure for the whole file
// system is provided. It also reports size of the data and metadata being
// stored, not the larger figure of the amount of space taken after redundancy is
// applied. So it is impossible to answer the question of how much disk space is
// being used in an individual device. Example output:
//
// 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
//
// Guesstimate the per device used figure as the fraction of the file system wide
// extent usage based on chunk usage per device.
//
// Positives:
// 1) Per device used figure will correctly be between zero and allocated chunk
// size.
//
// Known inaccuracies:
// [for single and multi-device btrfs file systems]
// 1) Btrfs filesystem show reports file system wide file extent usage without
// considering redundancy applied to that data. (By default btrfs stores two
// copies of metadata and one copy of data).
// 2) At minimum size when all data has been consolidated there will be a few
// partly filled chunks of 256 MiB or more for data and metadata of each
// storage profile (RAID level).
// [for multi-device btrfs file systems only]
// 3) Data may be far from evenly distributed between the chunks on multiple
// devices.
// 4) Extents can be and are relocated to other devices within the file system
// when shrinking a device.
if ( btrfs_found )
exit_status = Utils::execute_command( "btrfs filesystem show " + partition .get_path(), output, error, true ) ;
else
exit_status = Utils::execute_command( "btrfs-show " + partition .get_path(), output, error, true ) ;
if ( ! exit_status )
{
//FIXME: Improve free space calculation for multi-device
// btrfs file systems. Currently uses the size of the
// btrfs device in this partition (spot on) and the
// file system wide used bytes (wrong for multi-device
// file systems).
//Extract the per device size figure. Guesstimate the per device used
// figure as discussed above. Example output:
//
// 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
//
// Calculations:
// ptn fs size = devid size
// ptn fs used = total fs used * devid used / sum devid used
Byte_Value ptn_bytes = partition .get_byte_length() ;
Byte_Value ptn_size = partition .get_byte_length() ;
Byte_Value total_fs_used = -1 ; //total fs used
Byte_Value sum_devid_used = 0 ; //sum devid used
Byte_Value devid_used = -1 ; //devid used
Byte_Value devid_size = -1 ; //devid size
//Btrfs file system wide used bytes (extents and items)
Glib::ustring str ;
//Btrfs file system device size
Glib::ustring regexp = "devid .* size ([0-9\\.]+( ?[KMGTPE]?i?B)?) .* path " + partition .get_path() ;
if ( ! ( str = Utils::regexp_label( output, regexp ) ) .empty() )
T = btrfs_size_to_num( str, ptn_bytes, true ) ;
//Btrfs file system wide used bytes
if ( ! ( str = Utils::regexp_label( output, "FS bytes used ([0-9\\.]+( ?[KMGTPE]?i?B)?)" ) ) .empty() )
N = T - btrfs_size_to_num( str, ptn_bytes, false ) ;
total_fs_used = Utils::round( btrfs_size_to_gdouble( str ) ) ;
if ( T > -1 && N > -1 )
Glib::ustring::size_type offset = 0 ;
Glib::ustring::size_type index ;
while ( ( index = output .find( "devid ", offset ) ) != Glib::ustring::npos )
{
T = Utils::round( T / double(partition .sector_size) ) ;
N = Utils::round( N / double(partition .sector_size) ) ;
partition .set_sector_usage( T, N );
Glib::ustring devid_path = Utils::regexp_label( output .substr( index ),
"devid .* path (/dev/[[:graph:]]+)" ) ;
if ( ! devid_path .empty() )
{
//Btrfs per devid used bytes (chunks)
Byte_Value used = -1 ;
if ( ! ( str = Utils::regexp_label( output .substr( index ),
"devid .* used ([0-9\\.]+( ?[KMGTPE]?i?B)?) path" ) ) .empty() )
{
used = btrfs_size_to_num( str, ptn_size, false ) ;
sum_devid_used += used ;
if ( devid_path == partition .get_path() )
devid_used = used ;
}
if ( devid_path == partition .get_path() )
{
//Btrfs per device size bytes (chunks)
if ( ! ( str = Utils::regexp_label( output .substr( index ),
"devid .* size ([0-9\\.]+( ?[KMGTPE]?i?B)?) used " ) ) .empty() )
devid_size = btrfs_size_to_num( str, ptn_size, true ) ;
}
}
offset = index + 5 ; //Next find starts immediately after current "devid"
}
if ( total_fs_used > -1 && devid_size > -1 && devid_used > -1 && sum_devid_used > 0 )
{
T = Utils::round( devid_size / double(partition .sector_size) ) ; //ptn fs size
double ptn_fs_used = total_fs_used * ( devid_used / double(sum_devid_used) ) ; //ptn fs used
N = T - Utils::round( ptn_fs_used / double(partition .sector_size) ) ;
partition .set_sector_usage( T, N ) ;
}
}
else