Add channel program for taking recursive snapshots based on property

[clinta]

Motivation and Context

This is a contribution of a channel program that takes recursive snapshots as suggested by @kpande in #8443 .

Description

Creates the directory contrib/zcp where useful community maintained channel programs can kept and starts with a channel program to satisfy the request in #8443.

How Has This Been Tested?

Successfully ran the channel program.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.

[clinta]

Added the ability to specify the property as an optional argument
Usage: zfs program <pool> autosnap.lua [noop] [<property>] <snapshot>

[clinta]

The <pool> parameter is required by zfs program, but the channel program itself operates on whatever dataset you specify, just as if you did zfs snapshot.

So zfs program tank autosnap.lua tank/foo/bar@backup only creates tank/foo/bar@backup and @backup snapshots of any child datasets of tank/foo/bar. It does not touch anything else in the tank pool.

[behlendorf]

This is great, I think having useful example channel programs in contrib will be very helpful.

Would it be worthwhile to consider going one step father and include these examples in the packages? If so, where would be the best place to install them by default? Are there other existing scripts we should consider adding at the same time?

Either way, we'll need to make sure these new files are tracked by the build system. You'll need to add a Makefile.am to the new zcp directory, until we determine where these should be installed it can be very simple, just one line should work.

nodist_zcp_SCRIPTS = autosnap.lua

And add the new directory to SUBDIRS and DIST_SUBDIRS in contrib/Makefile.am, and lastly reference the new Makefile in the top-level configure.ac. Like so.

diff --git a/configure.ac b/configure.ac
index 9e4f8ff11830..ea8dc872a755 100644
--- a/configure.ac
+++ b/configure.ac
@@ -133,6 +133,7 @@ AC_CONFIG_FILES([
        contrib/initramfs/hooks/Makefile
        contrib/initramfs/scripts/Makefile
        contrib/initramfs/scripts/local-top/Makefile
+       contrib/zcp/Makefile
        contrib/pyzfs/Makefile
        contrib/pyzfs/setup.py
        module/Makefile
diff --git a/contrib/Makefile.am b/contrib/Makefile.am
index 81926a83ee69..9a82f82ee387 100644
--- a/contrib/Makefile.am
+++ b/contrib/Makefile.am
@@ -1,2 +1,2 @@
-SUBDIRS = bash_completion.d dracut initramfs pyzfs
-DIST_SUBDIRS = bash_completion.d dracut initramfs pyzfs
+SUBDIRS = bash_completion.d dracut initramfs pyzfs zcp
+DIST_SUBDIRS = bash_completion.d dracut initramfs pyzfs zcp

[behlendorf]

It'd be nice to include the proposed fix, adding the + prefix to optstring from #9056 (comment) so we wouldn't need this workaround. Applying it only to zfs program for now should minimize any potential compatibility problems.

[clinta]

Should that be included here, or should that fix be it's own PR?

[clinta]

@behlendorf thanks to your comments on #9056 I was able to remove the workaround and just document that the program needs to be called with a -- between the name of the script and the parameters.

This makes the argument processing quite a bit simpler and no longer position dependent.

The usage is now zfs program <pool> autosnap.lua -- [-n] [-p <property>] <snapshot>

[clinta]

Still struggling to get this to build. Looks like there's something more is need in contrib/zcp/Makefile.am.

The TEST builds are failing with make[5]: *** No rule to make target 'autosnap.lua', needed by 'all-am'. Stop.

[behlendorf]

@clinta sorry about the Makefile.am, for now let's keep it super simple. This should work.

-zcpdir = $(datarootdir)/zcp
-nodist_zcp_SCRIPTS = autosnap.lua
+EXTRA_DIST = autosnap.lua

[Fabian-Gruenbichler]

On Wed, Jul 17, 2019 at 05:31:50PM -0700, Brian Behlendorf wrote: Would it be worthwhile to consider going one step father and include these examples in the packages? If so, where would be the best place to install them by default? Are there other existing scripts we should consider adding at the same time?

in Debian (and derivatives), examples usually go into /usr/share/doc/<PACKAGE>/examples that's also where the vdev_id.conf examples are shipped, for example. maybe a subdir for zcp?

[codecov]

Codecov Report

Merging #9050 into master will decrease coverage by 12.15%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #9050       +/-   ##
===========================================
- Coverage   78.67%   66.51%   -12.16%     
===========================================
  Files         400      325       -75     
  Lines      121009   103708    -17301     
===========================================
- Hits        95199    68982    -26217     
- Misses      25810    34726     +8916

Flag	Coverage Δ
#kernel	?
#user	66.51% <ø> (+0.14%)	⬆️

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[clinta]

I'm looking at some of the zcp tests and I think I should be able to add testing for this program.

[behlendorf]

Let's go ahead and add this to contrib/zcp for the moment, then we can follow up as needed with changes to potentially install it and add some test coverage.