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<html><head><title>StGIT Wiki: StGITtheory</title><link type="text/css" rel="stylesheet" href="/cgi-bin/wiki.cgi/StyleSheetPage?raw=3" /><meta name="robots" content="INDEX,NOFOLLOW" /><link rel="alternate" type="application/rss+xml" title="StGIT Wiki" href="/cgi-bin/wiki.cgi?action=rss" /><link rel="alternate" type="application/rss+xml" title="StGIT Wiki: StGITtheory" href="/cgi-bin/wiki.cgi?action=rss;rcidonly=StGITtheory" /></head><body class="/cgi-bin/wiki.cgi"><div class="header"><span class="gotobar bar"><a class="local" href="/cgi-bin/wiki.cgi/HomePage">HomePage</a> <a class="local" href="/cgi-bin/wiki.cgi/RecentChanges">RecentChanges</a> </span><h1><a title="Click to search for references to this page" href="/cgi-bin/wiki.cgi?search=StGITtheory">StGITtheory</a></h1></div><div class="sidebar"></div><div class="content browse"><h2>A Bit of StGIT Patch Theory</h2><p>Every patch in <a class="local" href="/cgi-bin/wiki.cgi/StGIT">StGIT</a> is internally represented as two nodes - the bottom and the top. The nodes are commit IDs stored in the GIT object database. The actual patch is the diff between the trees corresponding to the bottom and the top nodes. This can be written as</p><pre class="real">P = diff(Nb, Nt)
P - patch
Nb - bottom (start) node
Nt - top (end) node
</pre><p>The order of diff arguments is (old, new).</p><p>For an ordered stack of patches:</p><pre class="real">P1 = diff(N0, N1)
P2 = diff(N1, N2)
...
Ps = P1 + P2 + P3 + ... = diff(Nsb, Nst)
Ps - the cumulative patch of the whole stack
Nsb - bottom stack node (same as N0)
Nst - top stack node (same as Nn)
</pre><p>The plus sign presents superposition of patches. Please note that such superposition is not always commutative.</p><p>Whenever <a class="local" href="/cgi-bin/wiki.cgi/StGIT">StGIT</a> pulls changes from another repository, it unapplies (pops) all applied patches, updates the branch using git commands and tries to re-apply (push) the patches that were applied.</p><p>Popping a patch from the stack is done by simply setting the stack top Nst to the patch bottom Nb. Pushing is not always trivial and may need merging.</p><p>When pushing an unapplied patch P from the stack, it may happen that the patch bottom Nb is different from the stack top Nst, i.e. the patch was originally applied to a different tree. In this case, the patch needs to be adjusted to its new position on the stack. First, the new stack top is calculated by diff3 merging:</p><pre class="real">Nst' = diff3(Nst, Nb, Nt)
</pre><p>The order of diff3 parameters is (branch1, ancestor, branch2).</p><p>If the merge succeeds, the patch is adjusted as following:</p><pre class="real">Nb' = Nst
Nt' = Nst'
P' = diff(Nb', Nt')
</pre><p>Nb' and Nt' become the new bottom and top nodes of the patch, and the stack top is advanced to Nst'.</p><p>If the the merge fails, the user is requested to resolve conflicts and refresh the patch by "stg refresh". It is also possible to undo the failed push by "stg push --undo".</p><p>This approach allows easy reordering of patches. To reorder applied patches, the user should pop them first and then push them back to the stack in the desired order. Unless the patches modify the same or adjacent lines in the same files, <a class="local" href="/cgi-bin/wiki.cgi/StGIT">StGIT</a> should be able to adjust the patches automatically for the new order.</p><h2>Layout of the .git Directory</h2><pre class="real">branches/ remote branches to pull (deprecated)
hooks/ scripts executed by git on some events
info/
exclude list of files ignored for the purpose of commit
refs list of commit IDs from refs/ (used on servers)
objects/ git objects
00/ unpacked objects
...
ff/
info/
packs list of object packs
pack/ object packs
*.idx index files
*.pack actual pack files
patches/ storage for StGIT patches
master/ patches for the master branch
patches/ storage for individual patches
patch1/ name of one of the StGIT patches
authdate patch date
authemail author's e-mail
authname author's name
bottom bottom ID of the patch
bottom.old old bottom ID of the patch (for undo)
commemail committer's e-mail
commname committer's name
description patch description
top top ID of the patch
top.old old top ID of the patch (for undo)
patch2/ name of another StGIT patch
...
applied list of applied patches
current name of the topmost patch
description branch description
protected if present, the branch is protected against changes
unapplied list of unapplied patches
other-branch/ patches for "other-branch"
...
refs/ various significant commit IDs
bases/ bottom commit IDs of the patch stacks
heads/ top commit IDs of branches
patches/ commit IDs of StGIT patches
tags/ commit IDs of tags (commit and tag objects)
remotes/ remote branches to pull and push
FETCH_HEAD list of fetched branches and their commit IDs
HEAD reference to the current branch
ORIG_HEAD previous commit ID of the head branch
config configuration of the repository
description description of the repository
index directory cache
</pre></div><div class="footer"><hr /><span class="gotobar bar"><a class="local" href="/cgi-bin/wiki.cgi/HomePage">HomePage</a> <a class="local" href="/cgi-bin/wiki.cgi/RecentChanges">RecentChanges</a> </span><span class="edit bar"><br /> <a class="local" href="/cgi-bin/wiki.cgi/Comments_On_StGITtheory">Comments On StGITtheory</a> <a href="/cgi-bin/wiki.cgi?action=password">This page is read-only</a> <a class="history" href="/cgi-bin/wiki.cgi?action=history;id=StGITtheory">View revisions</a> <a class="admin" href="/cgi-bin/wiki.cgi?action=admin;id=StGITtheory">Administration</a> <a href="http://www.memebot.com">Memebot</a> <a href="http://www.oddmuse.org">Oddmuse</a></span><span class="time"><br /> Last edited 2006-05-09 00:08 UTC by <a class="author" title="from h-64-105-159-118.phlapafg.covad.net" href="/cgi-bin/wiki.cgi/proski">proski</a> <a class="diff" href="/cgi-bin/wiki.cgi?action=browse;diff=2;id=StGITtheory">(diff)</a></span><form method="get" action="/cgi-bin/wiki.cgi" enctype="multipart/form-data" class="search">
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