From 13c08808ae96e7e00cbec779277ccc313c4fc9b9 Mon Sep 17 00:00:00 2001 From: Mike Fleetwood Date: Wed, 27 Jul 2022 23:06:57 +0100 Subject: [PATCH] Use btrfs inspect-internal dump-super to read usage (!105) GParted has been using 'btrfs filesystem show' to report file system usage but that doesn't work on a file system image so doesn't work in a GitLab CI test job, as discussed earlier in this patchset. There is 'btrfs inspect-internal min-dev-size' but: 1. That only works on a mounted file system and GParted isn't going to mount an unmounted file system just to query it's used space, so by extension won't work on image files. 2. It reports a figure which is almost the same as the chunk usage of the device within the btrfs file system. However if some files have been deleted leaving chunks partially used, then 'btrfs filesystem resize' will successfully shrink a btrfs smaller than the reported minimum device size. And there is also 'btrfs filesystem usage' but that also only works on a mounted file system. So instead use 'btrfs inspect-internal dump-super' to report some of the figures previously obtained from 'btrfs filesystem show'. For example for a single device btrfs in an image file: $ truncate -s 256M /tmp/test.img $ mkfs.btrfs /tmp/test.img $ btrfs inspect-internal dump-super /tmp/test.img | egrep 'total_bytes|bytes_used|sectorsize|devid' total_bytes 268435456 bytes_used 114688 sectorsize 4096 dev_item.total_bytes 268435456 dev_item.bytes_used 92274688 dev_item.devid 1 Comparing with results from 'btrfs filesystem show' for the same file system, after adding a loop device to allow 'btrfs filesystem show' to succeed: $ su - # losetup --find --show /tmp/test.img # btrfs filesystem show --raw /dev/loop0 Label: none uuid: 32a1eb31-4691-41ae-9ede-c45d723655a3 Total devices 1 FS bytes used 114688 devid 1 size 268435456 used 92274688 path /dev/loop0 This does bring a forced change in the calculation which affects multi- device btrfs file systems. 'btrfs filesystem show' provided chunk allocation information per device ("used" figure for each "devid"). The file system wide used bytes ("FS bytes used") was apportioned according to the fraction of the chunk allocation each device contained. However 'btrfs inspect-internal dump-super' doesn't provide chunk allocation information for all devices, only for the current device ("dev_item.bytes_used"). Instead the calculation now has to apportion the file system wide used bytes ("bytes_used") according to the fraction of the size of the current device ("dev_item.total_bytes") within the total size ("total_bytes"). This can't make any difference to a single device btrfs file system as both fractions will be 1. It only affects how the file system wide used bytes is distributed among multiple devices. As an example to see the difference between calculation methods, create a 2 GiB btrfs taking the defaults so getting duplicated metadata and single data. Add another 2 GiB partition and populate with some files. # mkfs.btrfs /dev/sdb1 btrfs-progs v4.15.1 See http://btrfs.wiki.kernel.org for more information. Label: (null) UUID: 68195e7e-c13f-4095-945f-675af4b1a451 Node size: 16384 Sector size: 4096 Filesystem size: 2.00GiB Block group profiles: Data: single 8.00MiB Metadata: DUP 102.38MiB System: DUP 8.00MiB SSD detected: no Incompat features: extref, skinny-metadata Number of devices: 1 Devices: ID SIZE PATH 1 2.00GiB /dev/sdb1 # mount /dev/sdb1 /mnt/1 # btrfs device add /dev/sdc1 /mnt/1 # cp -a /home/$USER/programming/c/gparted/ /mnt/1/ Usage figures using the old calculation apportioning file system wide usage according to chunk allocation per device: # btrfs filesystem show --raw /dev/sdb1 Label: none uuid: 68195e7e-c13f-4095-945f-675af4b1a451 Total devices 2 FS bytes used 178749440 devid 1 size 2147483648 used 239861760 path /dev/sdb1 devid 2 size 2147483648 used 436207616 path /dev/sdc1 sum_devid_used = 239861760 + 436207616 = 676069376 sdb1 usage = 178749440 * 239861760 / 676069376 = 63418277 sdc1 usage = 178749440 * 436207616 / 676069376 = 115331163 Usage figures using the new calculation apportioning file system wide usage according to device sizes: # btrfs inspect-internal dump-super /dev/sdb1 | egrep 'total_bytes|^bytes_used' total_bytes 4294967296 bytes_used 178749440 dev_item.total_bytes 2147483648 # btrfs inspect-internal dump-super /dev/sdc1 | egrep 'total_bytes|^bytes_used' total_bytes 4294967296 bytes_used 178749440 dev_item.total_bytes 2147483648 sdb1 usage = 178749440 * 2147483648 / 4294967296 = 89374720 sdc1 usage = 178749440 * 2147483648 / 4294967296 = 89374720 Both calculation methods ignore that btrfs allocates chunks at the volume manager level. So when fully compacted the last chunk for metadata and data for each storage profile (RAID level) will be partially filled and this is not accounted for. Also for multi-device btrfs file systems the new calculation provides different results. However given that shrinking a device in a multi- device btrfs file system can and does relocate extents to other devices (redundancy requirements of chunks permitting) it's minimum size is virtually impossible to calculate and may not restrict how small the btrfs device can be shrunk anyway. If it turns out that this new calculation causes problems it's been made a separate commit from the previous commit for easier reverting. Closes !105 - Update used btrfs file system commands, new minimum is btrfs-progs 4.5 --- src/btrfs.cc | 153 +++++++++++++++++++++------------------------------ 1 file changed, 64 insertions(+), 89 deletions(-) diff --git a/src/btrfs.cc b/src/btrfs.cc index 3514ab55..48b4ddb3 100644 --- a/src/btrfs.cc +++ b/src/btrfs.cc @@ -156,108 +156,83 @@ void btrfs::set_used_sectors(Partition& partition) // 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. + // device a complicated question to answer. Additionally, even if there is a + // correct answer for the usage / minimum size a device can be, a multi-device + // btrfs can and does relocate extents to other devices allowing it to be shrunk + // smaller than it's minimum size (redundancy requirements of chunks permitting). // - // 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: + // Btrfs inspect-internal dump-super provides chunk allocation information for the + // current device only and a single file system wide extent level usage figure. + // Calculate the per device used figure as the fraction of file system wide extent + // usage apportioned per device. // + // Example: // # btrfs filesystem show --raw /dev/sdb1 - // Label: none uuid: 003a619e-856f-4b9c-bd29-4d0ae0296d66 - // Total devices 2 FS bytes used 178765824 + // Label: none uuid: 68195e7e-c13f-4095-945f-675af4b1a451 + // Total devices 2 FS bytes used 178749440 // devid 1 size 2147483648 used 239861760 path /dev/sdb1 // devid 2 size 2147483648 used 436207616 path /dev/sdc1 // - // Guesstimate the per device used figure as the fraction of the file system wide - // extent usage based on chunk usage per device. + // # btrfs inspect-internal dump-super /dev/sdb1 | egrep 'total_bytes|bytes_used|sectorsize|devid' + // total_bytes 4294967296 + // bytes_used 178749440 + // sectorsize 4096 + // dev_item.total_bytes 2147483648 + // dev_item.bytes_used 239861760 + // dev_item.devid 1 // - // Positives: - // 1) Per device used figure will correctly be between zero and allocated chunk - // size. + // Calculation: + // ptn_fs_size = dev_item_total_bytes + // ptn_fs_used = bytes_used * dev_item_total_bytes / total_bytes // - // 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. - Utils::execute_command("btrfs filesystem show --raw " + Glib::shell_quote(partition.get_path()), + // This calculation also ignores that btrfs allocates chunks at the volume manager + // level. So when fully compacted there will be partially filled chunks for + // metadata and data for each storage profile (RAID level) not accounted for. + Utils::execute_command("btrfs inspect-internal dump-super " + Glib::shell_quote(partition.get_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. + // btrfs inspect-internal dump-super returns zero exit status for both success and + // failure. Instead use non-empty stderr to identify failure. + if (! error.empty()) + { + if (! output.empty()) + partition.push_back_message(output); + if (! error.empty()) + partition.push_back_message(error); + return; + } - // Extract the per device size figure. Guesstimate the per device used - // figure as discussed above. Example: - // - // # btrfs filesystem show --raw /dev/sdb1 - // Label: none uuid: 003a619e-856f-4b9c-bd29-4d0ae0296d66 - // Total devices 2 FS bytes used 178765824 - // devid 1 size 2147483648 used 239861760 path /dev/sdb1 - // devid 2 size 2147483648 used 436207616 path /dev/sdc1 - // - // Calculations: - // ptn fs size = devid size - // ptn fs used = total fs used * devid used / sum devid used - - long long total_fs_used = -1; - long long sum_devid_used = 0; - long long devid_used = -1; - long long devid_size = -1; - - // Btrfs file system wide used bytes (extents and items) - Glib::ustring::size_type index = output.find("FS bytes used"); + // Btrfs file system wide size (sum of devid sizes) + long long total_bytes = -1; + Glib::ustring::size_type index = output.find("\ntotal_bytes"); if (index < output.length()) - sscanf(output.substr(index).c_str(), "FS bytes used %lld", &total_fs_used); + sscanf(output.substr(index).c_str(), "\ntotal_bytes %lld", &total_bytes); - Glib::ustring::size_type offset = 0 ; - while ( ( index = output .find( "devid ", offset ) ) != Glib::ustring::npos ) + // Btrfs file system wide used bytes + long long bytes_used = -1; + index = output.find("\nbytes_used"); + if (index < output.length()) + sscanf(output.substr(index).c_str(), "\nbytes_used %lld", &bytes_used); + + // Sector size + long long sector_size = -1; + index = output.find("\nsectorsize"); + if (index < output.length()) + sscanf(output.substr(index).c_str(), "\nsectorsize %lld", §or_size); + + // Btrfs this device size + long long dev_item_total_bytes = -1; + index = output.find("\ndev_item.total_bytes"); + if (index < output.length()) + sscanf(output.substr(index).c_str(), "\ndev_item.total_bytes %lld", &dev_item_total_bytes); + + if (total_bytes > -1 && bytes_used > -1 && dev_item_total_bytes > -1 && sector_size > -1) { - Glib::ustring devid_path = Utils::regexp_label( output .substr( index ), - "devid .* path (/dev/[[:graph:]]+)" ) ; - if ( ! devid_path .empty() ) - { - // Btrfs per devid used bytes (chunks) - long long used = -1; - sscanf(output.substr(index).c_str(), "devid %*d size %*d used %lld path", &used); - if (used > -1) - { - 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) - sscanf(output.substr(index).c_str(), "devid %*d size %lld used", &devid_size); - } - 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 - { - if ( ! output .empty() ) - partition.push_back_message( output ); - - if ( ! error .empty() ) - partition.push_back_message( error ); + Sector ptn_fs_size = dev_item_total_bytes / partition.sector_size; + double devid_size_fraction = dev_item_total_bytes / double(total_bytes); + Sector ptn_fs_used = Utils::round(bytes_used * devid_size_fraction) / partition.sector_size; + Sector ptn_fs_free = ptn_fs_size - ptn_fs_used; + partition.set_sector_usage(ptn_fs_size, ptn_fs_free); + partition.fs_block_size = sector_size; } }