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| author | Al Viro <viro@zeniv.linux.org.uk> | 2010-01-16 14:10:21 -0500 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2010-03-03 13:00:23 -0500 |
| commit | 2f99cc6e4688faf5f03f9afe5e1c6097278c75b2 (patch) | |
| tree | 274933c56de5b24be3830f6faef6ca6d279a4ab9 | |
| parent | 796a6b521d0eadb338adf8cf7e482351c3a8a7b4 (diff) | |
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>
| -rw-r--r-- | Documentation/filesystems/sharedsubtree.txt | 16 |
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. |