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Commit 2f99cc6e authored by Al Viro's avatar Al Viro
Browse files

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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 796a6b52

Documentation/filesystems/sharedsubtree.txt

+15 −1
Original line number Diff line number Diff line
@@ -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.