250 lines
11 KiB
Markdown
250 lines
11 KiB
Markdown
A dear [[wishlist]] which would resolve [[this question|forum/ikiwiki_and_big_files]]: ikiwiki should support git-annex repositories.
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I am not sure how this would work, but from my POV, it should do a `git annex get` when new commits are pushed to its bare repo. This would assume, of course, that there's another repo somewhere that ikiwiki has access to, which works for HTTP-style remotes, but could be more problematic for SSH remotes that require a key.
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Another solution would be to make ikiwiki a remote itself and allow users to push big files to it. The only problem I see with this is those files would end up in the bare repository and not necessarily show up in the web rendering. Ideally, a big file pushed would be hardlinked between the two repos, but it seems [git-annex doesn't support that yet](http://git-annex.branchable.com/todo/wishlist:_use_hardlinks_for_local_clones). --[[anarcat]]
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> One technical problem with this is that ikiwiki doesn't allow symlinks
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> for [[security]], but git-annex relies on symlinks (unless you're in
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> direct mode, but I'm not sure that's really desirable here).
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> I'd like to make symlinks possible without compromising security,
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> but it'll be necessary to be quite careful. --[[smcv]]
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First implementation
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====================
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So as the [[discussion]] shows, it seems it's perfectly possible to actually do this! There's this [gallery site](http://stockholm.kalleswork.net) which uses the [[plugins/contrib/album]] plugin and git-annex to manage its files.
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The crucial steps are:
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1. setup a git annex remote in `$srcdir`
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2. configure direct mode because ikiwiki ignores symlinks for [[security]] reasons:
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cd $srcdir
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git annex init
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git annex direct
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3. configure files to be considered by git-annex (those will be not committed into git directly):
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git config annex.largefiles 'largerthan=100kb and not (include=*.mdwn or include=*.txt)'
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4. make the bare repository (the remote of `$srcdir`) ignored by git-annex:
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cd $srcdir
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git config remote.origin.annex-ignore true
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git config remote.origin.annex-sync false
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(!) This needs to be done on *ANY* clone of the repository, which is annoying, but it's important because we don't want to see git-annex stuff in the bare repo. (why?)
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5. deploy the following crappy plugin to make commits work again and make sure the right files are added in git-annex:
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[[!format perl """
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#!/usr/bin/perl
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package IkiWiki::Plugin::gitannex;
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use warnings;
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use strict;
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use IkiWiki 3.00;
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sub import {
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hook(type => "getsetup", id => "gitannex", call => \&getsetup);
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hook(type => "savestate", id => "gitannex", call => \&rcs_commit);
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# we need to handle all rcs commands maybe?
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}
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sub getsetup () {
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return
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plugin => {
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safe => 1, # rcs plugin
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rebuild => undef,
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section => "misc",
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},
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}
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# XXX: we want to copy or reuse safe_git
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sub rcs_commit (@) {
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chdir $config{srcdir};
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`git annex add --auto`;
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`git annex sync`;
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}
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sub rcs_commit_staged (@) {
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rcs_commit($@);
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}
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1
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"""]]
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This assumes you know what `srcdir`, `repository` and so on mean, if you forgot (like me), see this reference: [[rcs/git/]].
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What doesn't work
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-----------------
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* the above plugin is kind of flaky and ugly.
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* it's not an RCS plugin, but probably should be, replacing the git plugin, because really: git doesn't work at all anymore at this point
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What remains to be clarified
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----------------------------
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* how do files get pushed to the `$srcdir`? Only through the web interface?
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* why do we ignore the bare repository?
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See the [[discussion]] for a followup on that. --[[anarcat]]
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Alternative implementation
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==========================
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An alternative implementation, which remains to be detailed but is mentionned in [[forum/ikiwiki_and_big_files]], is to use the [[underlay]] feature combined with the `hardlink` option to deploy the git-annex'd files. Then git-annex is separate from the base ikiwiki git repo. See also [[tips/Ikiwiki_with_git-annex__44___the_album_and_the_underlay_plugins]] for an example.
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Also note that ikiwiki-hosting has a [patch waiting](https://ikiwiki-hosting.branchable.com/todo/git-annex_support) to allow pushes to work with git-annex. This could potentially be expanded to sync content to the final checkout properly, avoiding some of the problems above (esp. wrt to non-annex bare repos).
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Combined with the [[underlay]] feature, this could work very nicely indeed... --[[anarcat]]
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Here's an attempt:
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<pre>
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cd /home/user
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git clone source.git source.annex
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cd source.annex
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git annex direct
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cd ../source.git
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git annex group . transfer
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git remote add annex ../source.annex
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git annex sync annex
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</pre>
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Make sure the `hardlink` setting is enabled, and add the annex as an underlay, in `ikiwiki.setup`:
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<pre>
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hardlink: 1
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add_underlays:
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- /home/w-anarcat/source.annex
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</pre>
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Then moving files to the underlay is as simple as running this command in the bare repo:
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<pre>
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#!/bin/sh
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echo "moving big files to annex repository..."
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git annex move --to annex
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</pre>
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I have added this as a hook in `$HOME/source.git/hooks/post-receive` (don't forget to `chmod +x`).
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The problem with the above is that the underlay wouldn't work: for some reason it wouldn't copy those files in place properly. Maybe it's freaking out because it's a full copy of the repo... My solution was to make the source repository itself a direct repo, and then add it as a remote to the bare repo. --[[anarcat]]
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Back from the top
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=================
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Obviously, the final approach of making the `source` repository direct mode will fail because ikiwiki will try to commit files there from the web interface which will fail (at best) and (at worst) add big files into git-annex (or vice-versa, not sure what's worse actually).
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Also, I don't know how others here made the underlay work, but it didn't work for me. I think it's because in the "source" repository, there are (dead) symlinks for the annexed files. This overrides the underlay, because of [[security]] - although I am unclear as to why this is discarded so early. So in order to make the original idea above work properly (ie. having a separate git-annex repo in direct mode) work, we must coerce ikiwiki into tolerating symlinks in the srcdir a little more:
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<pre>
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diff --git a/IkiWiki.pm b/IkiWiki.pm
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index 1043ef4..949273c 100644
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--- a/IkiWiki.pm
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+++ b/IkiWiki.pm
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@@ -916,11 +916,10 @@ sub srcfile_stat {
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my $file=shift;
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my $nothrow=shift;
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- return "$config{srcdir}/$file", stat(_) if -e "$config{srcdir}/$file";
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- foreach my $dir (@{$config{underlaydirs}}, $config{underlaydir}) {
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- return "$dir/$file", stat(_) if -e "$dir/$file";
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+ foreach my $dir ($config{srcdir}, @{$config{underlaydirs}}, $config{underlaydir}) {
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+ return "$dir/$file", stat(_) if (-e "$dir/$file" && ! -l "$dir/$file");
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}
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- error("internal error: $file cannot be found in $config{srcdir} or underlay") unless $nothrow;
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+ error("internal error: $file cannot be found in $config{srcdir} or underlays @{$config{underlaydirs}} $config{underlaydir}") unless $nothrow;
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return;
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}
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diff --git a/IkiWiki/Render.pm b/IkiWiki/Render.pm
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index 9d6f636..e0b4cf8 100644
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--- a/IkiWiki/Render.pm
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+++ b/IkiWiki/Render.pm
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@@ -337,7 +337,7 @@ sub find_src_files (;$$$) {
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if ($underlay) {
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# avoid underlaydir override attacks; see security.mdwn
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- if (! -l "$abssrcdir/$f" && ! -e _) {
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+ if (1 || ! -l "$abssrcdir/$f" && ! -e _) {
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if (! $pages{$page}) {
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push @files, $f;
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push @IkiWiki::underlayfiles, $f;
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</pre>
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<del>Now obviously this patch is incomplete: I am not sure we actually avoid the attack, ie. i am not sure the check in `srcdir()` is sufficient to remove completely the check in `find_src_files()`.</del>
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After reviewing the code further, it seems that `find_src_files` in three places in ikiwiki:
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<pre>
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../IkiWiki/Render.pm:421: find_src_files(1, \@files, \%pages);
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../IkiWiki/Render.pm:846: ($files, $pages)=find_src_files();
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../po/po2wiki:18:my ($files, $pages)=IkiWiki::find_src_files();
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</pre>
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The first occurence is in `IkiWiki::Render::process_changed_files`, where it is used mostly for populating `@IkiWiki::underlayfiles`, the only side effect of
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`find_src_files`. The second occurence is in `IkiWiki::Render::refresh`. There things are a little more complicated (to say the least) and a lot of stuff happens. To put it in broad terms, first it does a `IkiWiki::Render::scan` and then a `IkiWiki::Render::render`. The last two call `srcfile()` appropriately (where i put an extra symlink check), except for `will_render()` in `scan`, which I can't figure out right now and that seems to have a lot of global side effects. It still looks fairly safe at first glance. The `rcs_get_current_rev`, `refresh`, `scan` and `rendered` hooks are also called in there, but I assume those to be safe, since they are called with sanitized values already.
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The patch does work: the files get picked up from the underlay and properly hardlinked into the target `public_html` directory! So with the above patch, then the following hook in `source.git/hooks/post-receive`:
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<pre>
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#!/bin/sh
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OLD_GIT_DIR="$GIT_DIR"
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unset GIT_DIR
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echo "moving big files to annex repository..."
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git annex copy --to annex
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git annex sync annex
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</pre>
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(I am not sure anymore why GIT_DIR is necessary, but I remember it destroyed all files in my repo because git-annex synced against the `setup` branch in the parent directory. fun times.)
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Then the `annex` repo is just a direct clone of the source.git:
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<pre>
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cd /home/user
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git clone --shared source.git annex
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cd annex
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git annex direct
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cd ../source.git
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git remote add annex ../annex
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</pre>
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And we need the following config:
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<pre>
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hardlink: 1
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add_underlays:
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- /home/w-anarcat/annex
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add_plugins:
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- underlay
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</pre>
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... and the `ikiwiki-hosting` patch mentionned earlier to allow git-annex-shell to run at all. Also, the `--shared` option will [make git-annex use hardlinks itself between the two repos](https://git-annex.branchable.com/todo/wishlist:_use_hardlinks_for_local_clones/), so the files will be available for download as well. --[[anarcat]]
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> <del>...aaaand this doesn't work anymore. :( i could have sworn this was working minutes ago, but for some reason the annexed files get skipped again now. :(</del> Sorry for the noise, the annex repo wasn't in direct mode - the above works! --[[anarcat]]
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This [[!taglink patch]] still applies - anything else I should be doing here to try to get this fixed? A summary maybe? --[[anarcat]]
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> Sorry, I don't have the mental bandwidth at the moment to work through the
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> implications of this change. I know you want this feature, I know it's an
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> attractive solution to several use cases, and git annex support is in the
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> queue, but at right now I'm still trying to deal with mitigating
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> CVE-2016-3714, and the last thing I want to do is merge new security
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> risks. --[[smcv]]
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> > No problem at all, glad that you still have that in the queue, and I hope
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> > my work was somewhat useful in pushing this forward! Thanks for taking
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> > care of the Imagetragick situation... :/ --[[anarcat]]
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Yet another option
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==================
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If you happen to use rsync to deploy, instead of git, this is [much easier](https://www.cs.unb.ca/~bremner/blog/posts/big-files).
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