Git and Submission¶

This page explains how released exercises get from the course repo onto your laptop, and how your work gets from your laptop into a repo your TA and professor can read. You will want it the first time oslings update refuses to run, and any time you are unsure whether what you typed today was actually saved. First-time setup lives in Dev Setup; this is the reference for what those commands do underneath.

Two remotes, one clone¶

You have one clone of one repository on your machine, with two remotes attached to it. Everything else follows from that.

Remote	Points at	Your access	Used by
`course`	the class repo	read only (fetch)	`oslings update`
`origin`	your private `oslings-<your-github-username>` repo	read and write	`oslings submit`

flowchart LR
    C["course\n(class repo, read-only)"] -- "oslings update\nfetch + merge" --> L["your clone\n(your laptop)"]
    L -- "oslings submit\nadd + commit + push" --> O["origin\n(your private repo)"]

oslings init-repo <url> builds this arrangement, and you run it once. It renames the clone's existing origin to course, adds your repo URL as the new origin, and pushes your current branch with -u so it tracks (sync.rs:50). Re-running it with a different URL is safe: it uses remote set-url when origin already exists (sync.rs:59). If your URL does not contain oslings-, it warns you — batch grading finds your repo by name.

Note what is not here: no per-exercise repo, no branch per exercise, no pull request. Exercises are gated by absence — one that has not been released exists in no commit you can fetch, so there is nothing to read ahead to.

What `oslings update` does¶

oslings update is a fetch and a merge, with two safety checks in front of it (sync.rs:86). In order:

Dirty check. Any uncommitted change — modified, staged, or untracked — under a course-owned path aborts the command before anything is fetched (sync.rs:97, git.rs:78).
Fetch. git fetch course. Nothing in your working tree changes yet.
Divergence check. git diff --name-only course/main...HEAD filtered to course-owned paths (git.rs:88). This catches edits you already committed to course files — the only thing a merge can conflict on.
Merge. git merge --no-edit course/main (sync.rs:129). Deliberately not --ff-only.
Report. It diffs info.toml before and after and prints the exercise names that are new (sync.rs:15). No new blocks means Already up to date — no new exercises.
Self-update. If the merge touched oslings-cli/, it re-runs cargo install --path oslings-cli --force for you (sync.rs:146).

oslings update --from <remote-or-path> pulls from somewhere other than course, which you will only use if an instructor tells you to.

Why there is a merge commit every time¶

Between two updates you make your own commits (every oslings submit is one), so your branch moves ahead while course/main moves ahead too. Two branches that both moved cannot fast-forward; git has to join them, and that join is the merge commit. Your history correctly looks like this:

* 4f1c2ab  Merge remote-tracking branch 'course/main'
|\
| * 9b0e771  release: ex07_scheduler        <- from course
* | 2d4a8e0  ex06_context_switch: submit (passing)   <- yours
* | 77c1d90  ex06_context_switch: submit (in progress)
|/
* 1a9f004  Merge remote-tracking branch 'course/main'

A merge commit per release is normal, harmless, and expected — not a mistake, and not something to rebase away. The merge is safe precisely because the two sides never write to the same files; see the ownership table below.

What `oslings submit` commits¶

oslings submit stages exactly these paths, skipping any that do not exist (sync.rs:183):

Path	What it holds
`my-work/`	your archived work, one directory per exercise
`submissions/`	snapshots taken when an exercise passed, plus `oslings-meta.toml`
`.oslings/state.toml`	which exercise you are on, what you have passed, hints used, test runs
`rv6/src`	the kernel you are building
`warmup/src`	the Module 1 Rust exercises

It then commits with the message <exercise>: submit (passing) or <exercise>: submit (in progress) depending on whether that exercise is in your completed list (sync.rs:32), and runs git push origin HEAD. If nothing is staged it prints Nothing new to submit. and stops — no empty commits.

Two things worth knowing:

Submit at the end of every session, red or green. All work happens in class, so this push is the record that you were here and working, and it is where you resume next time.
commands/src/bin and asmlab/src are not in that list. Work there reaches your repo when OSlings archives it into my-work/<exercise>/, which happens whenever you move off the exercise (model.rs:711). To push an in-progress command file before moving on, stage it yourself first: git add commands/src/bin and then oslings submit — submit commits whatever is already in the index.

Ignored on purpose, so do not go looking for them in your repo: target/, every Cargo.lock except the CLI's, .oslings/config.toml, and the oslings ship output (rv6/src/userbin/, rv6/src/userbin.rs). Command sources are committed; built images are not — see ulib and Commands.

Who owns which files¶

The whole design rests on the two sides never touching the same files.

Course-owned (guarded)	Student-owned
`exercises/`	`rv6/src`
`info.toml`	`warmup/src`
`oslings-cli/`	`commands/src/bin`
`setup.sh`, `SETUP.md`, `README.md`	`asmlab/src`
	`my-work/`, `submissions/`, `.oslings/state.toml`

The guarded list is literally COURSE_PATHS in git.rs:15; the staging directories are in model.rs:598. Everything else — the crate manifests (rv6/Cargo.toml, warmup/Cargo.toml, commands/Cargo.toml, ulib/), the linker scripts (rv6/kernel.ld, commands/user.ld), rust-toolchain.toml — is course-maintained but not guarded. Editing those will not stop update from starting, but if a later release changes the same file you get a real merge conflict at step 4, which is much less pleasant than the guard. Treat them as read-only.

When `update` refuses¶

This is the one failure mode worth understanding, and it has two forms.

"these course files have uncommitted changes"¶

You edited or created a file under a course-owned path and have not committed it. Common causes: a scratch note dropped in exercises/, hand-editing info.toml, an editor reformatting a file you had open. The error prints the exact fix:

git checkout -- exercises/ex07_scheduler/README.md
oslings update

Caveat the message does not spell out: git checkout -- restores tracked files only. If the offending path is a file you created, git checkout will error with did not match any file(s) known to git — move it out of the repo (or delete it) instead:

mv exercises/ex07_scheduler/notes.txt ~/Desktop/notes.txt

"you have committed changes to course files"¶

Same cause, but the edit is already in a commit, so discarding the working copy is not enough. Restore the course version from the upstream ref and commit that restoration:

git checkout course/main -- info.toml
git commit -m "restore course files"
oslings update

Your own work is never at risk in either case: both guards run before the merge and neither touches rv6/src, warmup/src, my-work/, or submissions/. If the merge fails anyway, oslings tells you to stop — do that, and ask a TA rather than experimenting with git reset.

Git for people who have not used it much¶

You can pass this course knowing five ideas.

Commit — a saved snapshot of the whole project with a message attached. Snapshots are cheap and permanent; nothing in a commit is lost.
Working tree — the files as they are right now on disk. Changes here are not saved until a commit.
Staging area (index) — what git add puts files into; git commit saves exactly what is staged. oslings submit does both for you.
Remote — a copy of the repository living on GitHub. push sends your commits there; fetch brings theirs down.
Merge — joining two lines of history. Normal here, once per release.

Useful, and safe to run any time:

Command	Tells you
`git status`	what has changed and what is staged
`git log --oneline --graph -20`	your recent history, merges and all
`git remote -v`	that `origin` is yours and `course` is the class repo
`git diff`	the exact lines you changed since your last commit

Avoid git reset --hard, git rebase, git push --force, and git checkout <branch> unless a TA is watching — those are the commands that can actually destroy work, and none of them are needed in this course. Everything else is recoverable.

Two habits close every loop: oslings update at the start of a session, oslings submit at the end of it. See Using OSlings for the rest of the CLI and the Integrity Policy for what your commit history may contain.