libbtrfsutil: add btrfs_util_delete_subvolume()

[platform/upstream/btrfs-progs.git] / Documentation / btrfs-quota.asciidoc

diff --git a/Documentation/btrfs-quota.asciidoc b/Documentation/btrfs-quota.asciidoc
index ef2e5d3..85ebf72 100644 (file)
--- a/Documentation/btrfs-quota.asciidoc
+++ b/Documentation/btrfs-quota.asciidoc
@@ -15,24 +15,24 @@ The commands under *btrfs quota* are used to affect the global status of quotas
 of a btrfs filesystem. The quota groups (qgroups) are managed by the subcommand
 `btrfs qgroup`(8).
 
-NOTE: the qgroups are different than the traditional user quotas and designed
+NOTE: Qgroups are different than the traditional user quotas and designed
 to track shared and exclusive data per-subvolume.  Please refer to the section
 'HIERARCHICAL QUOTA GROUP CONCEPTS' for a detailed description.
 
 PERFORMANCE IMPLICATIONS
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
-When the quotas are turned on, they affect all extent processing, taking a
-performance hit. It is not recommended to turn on qgroups unless the user
+When quotas are activated, they affect all extent processing, which takes a
+performance hit. Activation of qgroups is not recommended unless the user
 intends to actually use them.
 
 STABILITY STATUS
 ~~~~~~~~~~~~~~~~
 
 The qgroup implementation has turned out to be quite difficult as it affects
-the core of the filesystem operation. The users have hit various corner cases
-over time, eg. wrong accounting or system instability. The situation is
-gradually improving but currently (4.7) there are still issues found and fixed.
+the core of the filesystem operation. Qgroup users have hit various corner cases
+over time, such as incorrect accounting or system instability. The situation is
+gradually improving and issues found and fixed.
 
 HIERARCHICAL QUOTA GROUP CONCEPTS
 ---------------------------------
@@ -52,7 +52,7 @@ On the other hand, the traditional approach has only a poor solution to
 restrict directories.
 At installation time, the harddisk can be partitioned so that every directory
 (eg. /usr, /var/, ...) that needs a limit gets its own partition.  The obvious
-problem is, that those limits cannot be changed without a reinstallation.  The
+problem is that those limits cannot be changed without a reinstallation.  The
 btrfs subvolume feature builds a bridge.  Subvolumes correspond in many ways to
 partitions, as every subvolume looks like its own filesystem.  With subvolume
 quota, it is now possible to restrict each subvolume like a partition, but keep
@@ -96,7 +96,23 @@ instead of '0/ID'.  For all higher levels, the ID can be chosen freely.
 Each qgroup can contain a set of lower level qgroups, thus creating a hierarchy
 of qgroups. Figure 1 shows an example qgroup tree.
 
-// TODO: insert Figure 1
+                          +---+
+                          |2/1|
+                          +---+
+                         /     \
+                   +---+/       \+---+
+                   |1/1|         |1/2|
+                   +---+         +---+
+                  /     \       /     \
+            +---+/       \+---+/       \+---+
+qgroups     |0/1|         |0/2|         |0/3|
+            +-+-+         +---+         +---+
+              |          /     \       /     \
+              |         /       \     /       \
+              |        /         \   /         \
+extents       1       2            3            4
+
+Figure1: Sample qgroup hierarchy
 
 At the bottom, some extents are depicted showing which qgroups reference which
 extents.  It is important to understand the notion of 'referenced' vs
@@ -165,7 +181,7 @@ own way how to integrate qgroups.
 `Replacement for partitions`
 
 The simplest use case is to use qgroups as simple replacement for partitions.
-Btrfs takes the disk as a whole, and /, /usr, /var etc.  are created as
+Btrfs takes the disk as a whole, and /, /usr, /var, etc. are created as
 subvolumes.  As each subvolume gets it own qgroup automatically, they can
 simply be restricted.  No hierarchy is needed for that.