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diff --git a/Documentation/filesystems/aufs/design/05wbr_policy.txt b/Documentation/filesystems/aufs/design/05wbr_policy.txt deleted file mode 100644 index 1726d5d06..000000000 --- a/Documentation/filesystems/aufs/design/05wbr_policy.txt +++ /dev/null @@ -1,51 +0,0 @@ - -# Copyright (C) 2005-2016 Junjiro R. Okajima - -Policies to Select One among Multiple Writable Branches ----------------------------------------------------------------------- -When the number of writable branch is more than one, aufs has to decide -the target branch for file creation or copy-up. By default, the highest -writable branch which has the parent (or ancestor) dir of the target -file is chosen (top-down-parent policy). -By user's request, aufs implements some other policies to select the -writable branch, for file creation several policies, round-robin, -most-free-space, and other policies. For copy-up, top-down-parent, -bottom-up-parent, bottom-up and others. - -As expected, the round-robin policy selects the branch in circular. When -you have two writable branches and creates 10 new files, 5 files will be -created for each branch. mkdir(2) systemcall is an exception. When you -create 10 new directories, all will be created on the same branch. -And the most-free-space policy selects the one which has most free -space among the writable branches. The amount of free space will be -checked by aufs internally, and users can specify its time interval. - -The policies for copy-up is more simple, -top-down-parent is equivalent to the same named on in create policy, -bottom-up-parent selects the writable branch where the parent dir -exists and the nearest upper one from the copyup-source, -bottom-up selects the nearest upper writable branch from the -copyup-source, regardless the existence of the parent dir. - -There are some rules or exceptions to apply these policies. -- If there is a readonly branch above the policy-selected branch and - the parent dir is marked as opaque (a variation of whiteout), or the - target (creating) file is whiteout-ed on the upper readonly branch, - then the result of the policy is ignored and the target file will be - created on the nearest upper writable branch than the readonly branch. -- If there is a writable branch above the policy-selected branch and - the parent dir is marked as opaque or the target file is whiteouted - on the branch, then the result of the policy is ignored and the target - file will be created on the highest one among the upper writable - branches who has diropq or whiteout. In case of whiteout, aufs removes - it as usual. -- link(2) and rename(2) systemcalls are exceptions in every policy. - They try selecting the branch where the source exists as possible - since copyup a large file will take long time. If it can't be, - ie. the branch where the source exists is readonly, then they will - follow the copyup policy. -- There is an exception for rename(2) when the target exists. - If the rename target exists, aufs compares the index of the branches - where the source and the target exists and selects the higher - one. If the selected branch is readonly, then aufs follows the - copyup policy. |