zfsnap

want to contribute?

Awesome. Development primarily takes place on GitHub. Fork the repo, create a branch, hack in your feature, and send us a Pull Request.

If you have any questions, just email our mailing list (zfsnap@librelist.com).

If you found a bug, please report it via our issue tracker on GitHub.

We ask that you take the time to read the following developer notes so that your patches are more likely to be accepted.

Developer Notes

zfsnap is written in sh, avoiding bash-, ksh-, etc-specific features. Good old, simple sh. Though don't despair, it's surprisingly powerful.

Portability

Portability is key. When in doubt, if it isn't defined in POSIX, then don't use it. Exceptions are made (such as the choice to use "local" variables), but are rare.

Thankfully, ZFS is relatively modern (it was first introduced in Solaris 10), so the shells supported are comparatively featureful and complete.

OS checks are frowned upon; please keep the code as platform agnostic as possible.

Performance

As a rule, avoid calling external programs (date, grep, sed, etc). Adding a call or two per run isn't a problem, but adding a call that will execute for every snapshot checked will cause major slowdowns. Remember, zfsnap runs on systems with 100,000+ snapshots to check. sh's substring support is powerful enough that sed and grep are rarely (if ever) needed in our use-case.

Also avoid spawning subshells, which are almost as bad as calling external programs. $(), ``, and | each invoke subshells; if you need to return a value from a function, use the global variable RETVAL.

Tests

When submitting a patch, it is infinitely more likely to be accepted if it comes with tests.

References

Man pages are usually the best source of information when it comes to features and portability. sh's man page for any given OS is usually available somewhere on the internet.

The book "Beginning Portable Shell Scripting From Novice to Professional" is also a great reference, and has proven to be invaluable at times. It focuses on portability across Bourne and Bourne-like shells.