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Diffstat (limited to 'Documentation/filesystems/aufs/design/08shwh.txt')
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diff --git a/Documentation/filesystems/aufs/design/08shwh.txt b/Documentation/filesystems/aufs/design/08shwh.txt deleted file mode 100644 index ad58ebe15..000000000 --- a/Documentation/filesystems/aufs/design/08shwh.txt +++ /dev/null @@ -1,39 +0,0 @@ - -# Copyright (C) 2005-2016 Junjiro R. Okajima - -Show Whiteout Mode (shwh) ----------------------------------------------------------------------- -Generally aufs hides the name of whiteouts. But in some cases, to show -them is very useful for users. For instance, creating a new middle layer -(branch) by merging existing layers. - -(borrowing aufs1 HOW-TO from a user, Michael Towers) -When you have three branches, -- Bottom: 'system', squashfs (underlying base system), read-only -- Middle: 'mods', squashfs, read-only -- Top: 'overlay', ram (tmpfs), read-write - -The top layer is loaded at boot time and saved at shutdown, to preserve -the changes made to the system during the session. -When larger changes have been made, or smaller changes have accumulated, -the size of the saved top layer data grows. At this point, it would be -nice to be able to merge the two overlay branches ('mods' and 'overlay') -and rewrite the 'mods' squashfs, clearing the top layer and thus -restoring save and load speed. - -This merging is simplified by the use of another aufs mount, of just the -two overlay branches using the 'shwh' option. -# mount -t aufs -o ro,shwh,br:/livesys/overlay=ro+wh:/livesys/mods=rr+wh \ - aufs /livesys/merge_union - -A merged view of these two branches is then available at -/livesys/merge_union, and the new feature is that the whiteouts are -visible! -Note that in 'shwh' mode the aufs mount must be 'ro', which will disable -writing to all branches. Also the default mode for all branches is 'ro'. -It is now possible to save the combined contents of the two overlay -branches to a new squashfs, e.g.: -# mksquashfs /livesys/merge_union /path/to/newmods.squash - -This new squashfs archive can be stored on the boot device and the -initramfs will use it to replace the old one at the next boot. |