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+btrfs-qgroup - control the quota group of a btrfs filesystem
+*btrfs qgroup* <subcommand> <args>
+*btrfs qgroup* is used to control quota group(qgroup) of a btrfs filesystem.
+NOTE: To use qgroup, it needs to enable quota first using *btrfs quota*
+WARNING: Qgroup is not stable yet and will impact performance in current mainline
+kernel(v3.14 so far).
+Quota group or qgroup in btrfs has its hierarchy like subvolume.
+One subvolume/snapshot can reach its quota limits if it consumes all the quota
+assigned to it or any of the parent qgroup(s).
+Also for snapshot, it consumes no quota initially since all its data
+shares with its parent, so only modification in snapshot consumes quota.
+Every subvolume/snapshot will have its own qgroup with id '0/<subvolume id>'
+upon creating, but can be later destroyed by *btrfs qgroup destroy* command.
+NOTE: If the qgroup of a subvolume is destroyed, quota about the subvolume
+will not be functional until qgroup '0/<subvolume id>' is created again.
+*assign* <src> <dst> <path>::
+Assign qgroup <src> as the child qgroup of <dst> in the btrfs filesystem
+identified by <path>.
+*create* <qgroupid> <path>::
+Create a subvolume quota group.
+For the '0/<subvolume id>' qgroup, a qgroup can be created even before the
+subvolume created.
+*destroy* <qgroupid> <path>::
+Destroy a qgroup.
+If a qgroup is no isolated,which means it is a parent or child qgroup, it
+can't be destroyed.
+*limit* [options] <size>|none [<qgroupid>] <path>::
+Limit the size of a qgroup to <size> or no limit in the btrfs filesystem
+identified by <path>.
+If <qgroupid> is not given, qgroup of the subvolume identified by <path>
+is used if possible.
+limit amount of data after compression. This is the default, it is currently not
+possible to turn off this option.
+limit space exclusively assigned to this qgroup.
+*remove* <src> <dst> <path>::
+Remove the relationship between child qgroup <src> and parent qgroup <dst> in
+the btrfs filesystem identified by <path>.
+*show* [options] <path>::
+Show all qgroups in the btrfs filesystem identified by <path>.
+print parent qgroup id.
+print child qgroup id.
+print limit of referenced size of qgroup.
+print limit of exclusive size of qgroup.
+list all qgroups which impact the given path(include ancestral qgroups)
+list all qgroups which impact the given path(exclude ancestral qgroups)
+raw numbers in bytes, without the 'B' suffix.
+print human friendly numbers, base 1024, this is the default
+select the 1024 base for the following options, according to the IEC standard.
+select the 1000 base for the following options, according to the SI standard.
+show sizes in KiB, or kB with --si.
+show sizes in MiB, or MB with --si.
+show sizes in GiB, or GB with --si.
+show sizes in TiB, or TB with --si.
+list qgroups in order of <attr>.
+<attr> can be one or more of qgroupid,rfer,excl,max_rfer,max_excl.
+Prefix \'+' means ascending order and \'-' means descending order of <attr>.
+If no prefix is given, use ascending order by default.
+If multiple <attr>s is given, use comma to separate.
+*btrfs qgroup* returns a zero exit status if it succeeds. Non zero is
+returned in case of failure.
+*btrfs* is part of btrfs-progs.
+Please refer to the btrfs wiki for
+further details.