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worked out more design

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Joey Hess 2012-12-04 17:52:23 -04:00
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doc/design/assistant/desymlink.mdwn
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@ -40,3 +40,36 @@ With real files, some other standin for a missing file would be needed.
Perhaps a 0 length, unreadable, unwritable file? On systems that
support symlinks it could be a broken symlink like is used now, that
is converted to a real file when it becomes present.
## concrete design
* Enable with annex.nosymlink or such config option.
* Use .git/ for the git repo, but `.git/annex/objects` won't be used.
* `git status` and similar will show all files as type changed, and
`git commit` would be a very bad idea. Just don't support users running
git commands that affect the repository in this mode.
* However, `git status` and similar also will show deleted and new files,
which will be helpful for the assistant to use when starting up.
* Cache the mtime, size etc of files, and use this to detect when they've been
modified when the assistant was not running. This would only need to be
checked at startup, probably.
* Use dangling symlinks for standins for missing content, as now.
This allows just cloning one of these repositories normally, and then
as the files are synced in, they become real files.
* Maintain a local mapping from keys to files in the tree. This is needed
when sending/receiving keys to know what file to access. Note that a key
can map to multiple files. And that when a file is deleted or moved, the
mapping needs to be updated.
* May need a reverse mapping, from files in the tree to keys? TBD
* The existing watch code detects when a file gets closed, and in this
mode, it could be a new file, or a modified file, or an unchanged file.
For a modified file, can compare mtime, size, etc, to see if it needs
to be re-added.
* The inotify/kqueue interface does not tell us when a file is renamed.
So a rename has to be treated as a delete and an add, so can have a lot
of overhead, to re-hash the file.
* Note that this could be used without the assistant, as a git remote
that content is transferred to and from. Without the assistant, changes
to files in this remote would not be noticed and committed, unless
a git-annex command were added to do so.
Getting it basically working as a remote would be a good 1st step.