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authorAl Viro <viro@zeniv.linux.org.uk>2010-01-16 14:10:21 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2010-03-03 13:00:23 -0500
commit2f99cc6e4688faf5f03f9afe5e1c6097278c75b2 (patch)
tree274933c56de5b24be3830f6faef6ca6d279a4ab9 /Documentation/filesystems/sharedsubtree.txt
parent796a6b521d0eadb338adf8cf7e482351c3a8a7b4 (diff)
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add several pieces to shared subtree documentation
* document locking * add the missing part of data structure invariants (relationship between mnt_share and mnt_slave lists in case of a peer group among slaves). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'Documentation/filesystems/sharedsubtree.txt')
-rw-r--r--Documentation/filesystems/sharedsubtree.txt16
1 files changed, 15 insertions, 1 deletions
diff --git a/Documentation/filesystems/sharedsubtree.txt b/Documentation/filesystems/sharedsubtree.txt
index 23a181074f94..fc0e39af43c3 100644
--- a/Documentation/filesystems/sharedsubtree.txt
+++ b/Documentation/filesystems/sharedsubtree.txt
@@ -837,6 +837,9 @@ replicas continue to be exactly same.
individual lists does not affect propagation or the way propagation
tree is modified by operations.
+ All vfsmounts in a peer group have the same ->mnt_master. If it is
+ non-NULL, they form a contiguous (ordered) segment of slave list.
+
A example propagation tree looks as shown in the figure below.
[ NOTE: Though it looks like a forest, if we consider all the shared
mounts as a conceptual entity called 'pnode', it becomes a tree]
@@ -874,8 +877,19 @@ replicas continue to be exactly same.
NOTE: The propagation tree is orthogonal to the mount tree.
+8B Locking:
+
+ ->mnt_share, ->mnt_slave, ->mnt_slave_list, ->mnt_master are protected
+ by namespace_sem (exclusive for modifications, shared for reading).
+
+ Normally we have ->mnt_flags modifications serialized by vfsmount_lock.
+ There are two exceptions: do_add_mount() and clone_mnt().
+ The former modifies a vfsmount that has not been visible in any shared
+ data structures yet.
+ The latter holds namespace_sem and the only references to vfsmount
+ are in lists that can't be traversed without namespace_sem.
-8B Algorithm:
+8C Algorithm:
The crux of the implementation resides in rbind/move operation.