ZFS feature notifications

[Matthew Ahrens]

As discussed at the December OpenZFS Leadership Meeting[1], we would like
to make sure that all stakeholders are informed of important proposed
changes, regardless of what platform they originate on (Linux, illumos,
FreeBSD, etc).  This will help us get input from the best experts at code
review time.  "Important" changes include:
 - adding (or removing!) a new user-visible feature, no matter how small
    (e.g. adding a new CLI flag)
 - changing the user-visible behavior of existing features
    (e.g. now X will automatically do Y for you)
 - changing the on-disk format
    (e.g. to improve performance)
 - changing the zfs send stream format

As a rule of thumb, if you are changing a manpage (other than to clarify
existing functionality), it's probably an "important" change.

The notification will occur via email to the developer at open-zfs.org mailing
list, so please join that list if you'd like to be informed about upcoming
important changes to OpenZFS.  If you have feedback on these changes,
please let the author know within 7 days.

This guideline applies to newly-proposed changes, not retroactively to open
PR's.  However, here are some examples of open PR's that would be
classified as "important":

https://github.com/openzfs/openzfs/pull/690 ("zfs allow" can take numeric
id)
https://github.com/openzfs/openzfs/pull/664 (new kstats)
https://github.com/openzfs/openzfs/pull/668 (SIGINT/SIGKILL can cancel
channel program)
https://github.com/openzfs/openzfs/pull/649 (add new functions to channel
programs)
https://github.com/openzfs/openzfs/pull/638 ("zfs send" handles SIGINFO)
https://github.com/zfsonlinux/zfs/pull/8238 (remove new subcommand)
https://github.com/zfsonlinux/zfs/pull/8044 (new compression algorithm)
https://github.com/zfsonlinux/zfs/pull/8255 (new property, subcommand)
https://github.com/zfsonlinux/zfs/pull/7958 (new on-disk format, send
stream format, subcommand)

--matt

[1]
https://docs.google.com/document/d/1w2jv2XVYFmBVvG1EGf-9A5HBVsjAYoLIFZAnWHhV-BM/edit