initial docs

README.md

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+# gerritcp
+A utility to copy changesets from one gerrit instance to another
+
+## Theory of operation
+The tool is built primarily for the use case of downstreaming coreboot into
+Chromium OS. If feasible, extension of its scope to other scenarios is welcome.
+
+The tool must:
+
+ * copy submitted changes from upstream to reviewable change sets
+   in downstream;
+ * mask out changes to a configured set of files;
+ * keep a configured set of files around that only exists in downstream;
+ * provide multiple work streams with well-defined semantics so that changes,
+   to a given subdirectory (originally: util/crossgcc) can be handled
+   separately from everything else;
+ * un-abandon change sets in downstream if they would be revived by some
+   transaction of this tool;
+ * skip change sets that are marked WIP in downstream;
+ * keep already downstreamed change sets alone, e.g. if they have been
+   reordered.
+
+gerritcp keeps a bare git repo for tracking both upstream and downstream.
+Its new commits are created by directly adding objects to the git repo so
+there's no current checked-out tree that can get out of sync.  It works its
+way backward in the source branch, collecting information about which work
+stream a change belongs to and if it is already present in downstream and
+usable. As soon as all work streams have a root change to work from, gerritcp
+works forward through the collected changes, creating new change sets and
+immediately pushing them to downstream gerrit (marking them unabandoned
+as necessary).
+
+A change is "usable" if it is not marked WIP and if it contains metadata
+of upstream's change submission process: WIP allows skipping changes, even
+the top-of-patchtree change, in case they need to be put aside for a while,
+e.g. when waiting for an accompanying fix. Checking for upstream's metadata
+ensures that the downstream change in question is a downstreamed change:
+There are sometimes changes that have been pushed (and reviewed) downstream
+first and then put upstream for submission when ready. These should be
+integrated with the history, but they shouldn't derail other upstream changes.
+
+When applying a change to downstream, several things needs to be taken care of:
+
+- Since it's possible that changes have been taken out of downstream's patch
+  train, gerritcp can't simply adopt the toplevel `tree` object of the
+  upstream commit. Even files can't be adopted 1:1 but need to be merged
+  because there might be changes to skip.
+- Since downstream handles a few files differently, these might have to be
+  skipped entirely, by dropping the downstream object ids into the upstream-ish
+  `tree` objects that result from the prior step.
+- For work streams, the right parent commit needs to be chosen: It must be
+  the work stream specific parent (if that one isn't merged already) or
+  the upstream parent (in other cases) to account for situations in which
+  commits in the work stream touch files outside its direct responsibility.
+
+Pushes to downstream need to be authenticated (as there needs to be enough
+access to gerrit to be able to unabandon changes), while pulls from upstream
+can be anonymous.
+
+## Configuration format
+
+Configuration is stored in a single file in yaml format:
+
+```yaml
+sites:
+  upstream|downstream:
+    url: string
+    repo: string
+    branch: string
+    authentication: none|cookie
+    cookieName: string
+    cookieVal: string
+
+workstreams:
+  {name}:
+    onlyIfTouching:
+      - string # paths
+      - ...
+    neverModify:
+      - string # paths
+      - ...
+```
+
+The coreboot.org -> chromiumos configuration can be found in chromium-coreboot.yaml.

chromium-coreboot.yaml

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+sites:
+  upstream:
+    url: https://review.coreboot.org/
+    repo: coreboot
+    branch: master
+    authentication: none
+  downstream:
+    url: https://chromium-review.googlsource.com/
+    repo: chromiumos/third_party/coreboot
+    branch: chromeos-2016.05
+    authentication: cookie
+    cookieName: o
+    cookieValue: {somefunnystring}
+
+workstreams:
+  main:
+    neverModify:
+      util/crossgcc/
+      3rdparty/
+      util/nvidia/cbootimage/
+      .checkpatch.conf
+      .gitmodules
+      OWNERS
+  coreboot-sdk:
+    onlyIfTouching:
+      util/crossgcc/
+    neverModify:
+      3rdparty/
+      util/nvidia/cbootimage/
+      .checkpatch.conf
+      .gitmodules
+      OWNERS