GParted is already reading /proc/partitions to get whole disk device
names. The file also contains the major, minor device number of every
partition. Use this information to pre-populate the cache in the
BlockSpecial class.
# cat /proc/partitions
major minor #blocks name
8 0 20971520 sda
8 1 512000 sda1
8 2 20458496 sda2
...
9 3 1047552 md3
259 2 262144 md3p1
259 3 262144 md3p2
...
253 0 18317312 dm-0
253 1 2097152 dm-1
253 2 8383872 dm-2
253 3 1048576 dm-3
Note that for Device-Mapper names (dm-*) the kernel is not using the
canonical user space names (mapper/*). There is no harm in
pre-populating the cache with these names and will help if tools report
them too. It is just that for DMRaid, LVM and LUKS, GParted uses the
canonical /dev/mapper/* names so will still have to call stat() once for
each such name.
For plain disks (sd*) and Linux Software RAID arrays (md*) the kernel
name is the common user space name too, therefore matches what GParted
uses and pre-populating does avoid calling stat() at all for these
names.
Bug 767842 - File system usage missing when tools report alternate block
device names
Creation of every BlockSpecial object used to result in a stat() OS
call. On one of my test VMs debugging with 4 disks and a few partitions
on each, GParted refresh generated 541 calls to stat() in the
BlockSpecial(name) constructor. However there were only 45 unique
names. So on average each name was stat()ed approximately 12 times.
Cache the major, minor number associated with each name after starting
with a cleared cache for each GParted refresh. This reduces these
direct calls to stat() to just the 45 unique names.
Bug 767842 - File system usage missing when tools report alternate block
device names
On some distributions having btrfs on top of LUKS encrypted partitions,
adding a second device and removing the first device used to mount the
file system causes GParted to no longer be able to report the file
system as busy or the mount points themselves.
For example, on CentOS 7, create a single btrfs file system and mount
it. The provided /dev/mapper/sdb1_crypt name is reported, via
/proc/mounts, as the mounting device:
# cryptsetup luksFormat --force-password /dev/sdb1
# cryptsetup luksOpen /dev/sdb1 sdb1_crypt
# mkfs.btrfs -L encrypted-btrfs /dev/mapper/sdb1_crypt
# mount /dev/mapper/sdb1_crypt /mnt/1
# ls -l /dev/mapper
total 0
lrwxrwxrwx. 1 root root 7 Jul 2 14:15 centos-root -> ../dm-1
lrwxrwxrwx. 1 root root 7 Jul 2 14:15 centos-swap -> ../dm-0
crw-------. 1 root root 10, 236 Jul 2 14:15 control
lrwxrwxrwx. 1 root root 7 Jul 2 15:14 sdb1_crypt -> ../dm-2
# fgrep btrfs /proc/mounts
/dev/mapper/sdb1_crypt /mnt/1 btrfs rw,seclabel,relatime,space_cache 0 0
Add a second device to the btrfs file system:
# cryptsetup luksFormat --force-password /dev/sdb2
# cryptsetup luksOpen /dev/sdb2 sdb2_crypt
# btrfs device add /dev/mapper/sdb2_crypt /mnt/1
# ls -l /dev/mapper
...
lrwxrwxrwx. 1 root root 7 Jul 2 15:12 sdb2_crypt -> ../dm-3
# btrfs filesystem show /dev/mapper/sdb1_crypt
Label: 'encrypted-btrfs' uuid: 45d7b1ef-820c-4ef8-8abd-c70d928afb49
Total devices 2 FS bytes used 32.00KiB
devid 1 size 1022.00MiB used 12.00MiB path /dev/mapper/sdb1_crypt
devid 2 size 1022.00MiB used 0.00B path /dev/mapper/sdb2_crypt
Remove the first mounting device from the btrfs file system. Now the
non-canonical name /dev/dm-3 is reported, via /proc/mounts, as the
mounting device:
# btrfs device delete /dev/mapper/sdb1_crypt /mnt/1
# btrfs filesystem show /dev/mapper/sdb2_crypt
Label: 'encrypted-btrfs' uuid: 45d7b1ef-820c-4ef8-8abd-c70d928afb49
Total devices 1 FS bytes used 96.00KiB
devid 2 size 1022.00MiB used 144.00MiB path /dev/mapper/sdb2_crypt
# fgrep btrfs /proc/mounts
/dev/dm-3 /mnt/1 btrfs rw,seclabel,relatime,space_cache 0 0
# ls -l /dev/dm-3
brw-rw----. 1 root disk 253, 3 Jul 2 15:12 /dev/dm-3
GParted loads the mount_info mapping from /proc/mounts and with it the
/dev/dm-3 name. When GParted is determining if the encrypted btrfs file
system is mounted or getting the mount points it is using the
/dev/mapper/sdb2_crypt name. Therefore no information is found and the
file system is incorrectly reported as unmounted.
Fix by changing mount_info and fstab_info to use BlockSpecial objects
instead of strings so that matching is performed by major, minor device
numbers rather than by string compare. Note that as BlockSpecial
objects are used as the key of std::map [1] mappings operator<() [2]
needs to be provided to order the key values.
[1] std::map
http://www.cplusplus.com/reference/map/map/
[2] std::map::key_comp
http://www.cplusplus.com/reference/map/map/key_comp/
Bug 767842 - File system usage missing when tools report alternate block
device names
In some cases creating an LVM2 Physical Volume on top of a DMRaid array
reports no usage information and this partition warning:
Unable to read the contents of this file system!
Because of this some operations may be unavailable.
The cause might be a missing software package.
The following list of software packages is required for lvm2
pv file system support: lvm2.
For example on Ubuntu 14.04 LTS (with GParted built with
--enable-libparted-dmraid) create an LVM2 PV in a DMRaid array
partition. GParted uses this command:
# lvm pvcreate -M 2 /dev/mapper/isw_bacdehijbd_MyArray0p2
But LVM reports the PV having a different name:
# lvm pvs
PV VG Fmt Attr PSize PFree
/dev/disk/by-id/dm-name-isw_bacdehijbd_MyArray0p2 lvm2 a-- 1.00g 1.00g
This alternate name is loaded into the LVM2_PV_Info module cache. Hence
when GParted queries partition /dev/mapper/isw_bacdehijbd_MyArray0p2 it
has no PV information against that name and reports unknown usage.
However they are actually the same block special device; major 252,
minor 2:
# ls -l /dev/mapper/isw_bacdehijbd_MyArray0p2
brw-rw---- 1 root disk 252, 2 Jul 2 11:09 /dev/mapper/isw_bacdehijbd_MyArray0p2
# ls -l /dev/disk/by-id/dm-name-isw_bacdehijbd_MyArray0p2
lrwxrwxrwx 1 root root 10 Jul 2 11:09 /dev/disk/by-id/dm-name-isw_bacdehijbd_MyArray0p2 -> ../../dm-2
# ls -l /dev/dm-2
brw-rw---- 1 root disk 252, 2 Jul 2 11:09 /dev/dm-2
To determine if two names refer to the same block special device their
major, minor numbers need to be compared, instead of string comparing
their names.
Implement class BlockSpecial which encapsulates the name and major,
minor numbers for a block special device. Also performs comparison as
needed. See bug 767842 comments 4 and 5 for further investigation and
decision for choosing to implement a class.
Replace name strings in the LVM2_PV_Info module with BlockSpecial
objects performing correct block special device comparison.
Bug 767842 - File system usage missing when tools report alternate block
device names
Mike Fleetwood