Linking or copying consistent metadata

[vladimir-v-diaz]

A contributor reports:

When making changes, always hard linking old versions to the current will result in all previous versions (1.root, 2.root, etc) pointing to the current (root.json).

Writing the consistent version and then linking the current to that (e.g. linking root.json -> 3.root.json) should work, but requires more changes because now "write current" doesn't happen in every case. Holding two copies is a small constant increase in storage (#versions -> #versions + 1)

Either solution is fine, I left the commented code to remind myself about the issue and clearly forgot to come back to it!

We probably want to support the second solution (for clients / devices with limited space). Creating a true copy or a hard link should also probably be an option (i.e., tuf.conf.consistent_method = copy (or link)).

[JustinCappos]

Did this get addressed? We discussed this a long ways back.

On Thu, Sep 29, 2016 at 10:02 AM, Vladimir Diaz [email protected]
wrote:

A contributor reports:

When making changes, always hard linking old versions to the current will
result in all previous versions (1.root, 2.root, etc) pointing to the
current (root.json).

Writing the consistent version and then linking the current to that (e.g.
linking root.json -> 3.root.json) should work, but requires more changes
because now "write current" doesn't happen in every case. Holding two
copies is a small constant increase in storage (#versions -> #versions + 1)

Either solution is fine, I left the commented code to remind myself about
the issue and clearly forgot to come back to it!

We probably want to support the second solution (for clients / devices
with limited space). Creating a true copy or a hard link should also
probably be an option (i.e., tuf.conf.consistent_method = copy (or link)).

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[vladimir-v-diaz]

I partially implemented this here: https://github.com/vladimir-v-diaz/tuf/blob/ecordell-root-versioning/tuf/repository_lib.py#L2015-L2047. The fix points root.json to specific consistent snapshots.

@kwang100 is working on the configurable option to either create a copy of the consistent snapshot, or a link to it.

Consistent snapshots are now written as follows:

[2016-10-18 17:33:53,016 UTC] [tuf.repository_lib] [INFO] [write_metadata_file:2031@repository_lib.py]
Creating a consistent snapshot for u'/home/vlad/projects/tuf/tests/tmp6TEQkg/tmpL3SxRM/repository/metadata.staged/root.json'

[2016-10-18 17:33:53,016 UTC] [tuf.repository_lib] [DEBUG] [write_metadata_file:2032@repository_lib.py]
Saving u'/home/vlad/projects/tuf/tests/tmp6TEQkg/tmpL3SxRM/repository/metadata.staged/2.root.json'

[2016-10-18 17:33:53,022 UTC] [tuf.repository_lib] [INFO] [write_metadata_file:2041@repository_lib.py]
Pointing u'/home/vlad/projects/tuf/tests/tmp6TEQkg/tmpL3SxRM/repository/metadata.staged/root.json' to the consistent snapshot.

[2016-10-18 17:33:53,023 UTC] [tuf.repository_lib] [INFO] [_write_compressed_metadata:2139@repository_lib.py]
Saving u'/home/vlad/projects/tuf/tests/tmp6TEQkg/tmpL3SxRM/repository/metadata.staged/2.root.json.gz'

[2016-10-18 17:33:53,029 UTC] [tuf.repository_lib] [INFO] [write_metadata_file:2045@repository_lib.py]
Not creating a consistent snapshot for u'/home/vlad/projects/tuf/tests/tmp6TEQkg/tmpL3SxRM/repository/metadata.staged/snapshot.json'
...

[vladimir-v-diaz]

This issue has now been fully addressed. Remaining feature (option to use either a hard link or file copy) merged in PR #385