Commits on Oct 29, 2017

1. oci/cas/dir: Only Clean .umoci-* directories …

   This allows the use of other non-flocking consumers (e.g. other CAS
   implementations) in the same base directory.  The '.umoci-*' approach
   was suggested by Aleksa [1] as a way to keep Clean from stepping on
   other consumers' toes.  I'd suggesting using pruneExpire for
   ModTime-based backstopping, but Aleksa was concerned about leaking
   temporary directories from crashed umoci runs, primarily for
   disk-space concerns [1].  The .umoci-* approach allows such abandoned
   cruft to be immediately cleaned, without worrying about clobbering
   non-umoci consumers and extentions (unless they use .umoci-*
   filenames, in which case they deserve it ;).
   
   Aleksa also mentioned that non-umoci consumers might currently be
   relying on umoci to clean up their abandoned cruft [1].  But we both
   agree that non-umoci consumers should be cleaning up after themselves
   and/or providing their own "cleanup anything abandoned by previous
   runs of my tool" functionality, and should not be relying on umoci to
   do that for them [2,3].
   
   I've gone with .umoci-* instead of Aleksa's .umoci-tmpdir, because I
   think the . prefix is a sufficient hint that these directories are
   umoci-specific scratch space.
   
   Removal errors (because of insufficient permissions, etc.) seemed like
   they should be non-fatal so we could continue to remove other cruft.
   However, I didn't want to silently ignore the failed removal.  In this
   commit, I log those errors with a "warning" level.
   
   The new cleanFile method gives us tighter scoping for the defer lock
   release / file close, because those fire on function-exit [4].  With
   the old code, we'd keep the removed directory file-descriptors and
   associated flocks while Clean processed further directories.  With the
   new code, we release those resources immediately after we finish
   processing the directory in question.
   
   [1]: https://github.com/openSUSE/umoci/pull/198#issuecomment-337889528
   [2]: https://github.com/openSUSE/umoci/pull/198#issuecomment-337928272
   [3]: https://github.com/openSUSE/umoci/pull/198#issuecomment-337937858
   [4]: https://golang.org/ref/spec#Defer_statements
   
   Signed-off-by: W. Trevor King <wking@tremily.us>

   

   wking authored and cyphar committed Oct 29, 2017
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