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[RFC] overlay: make sure directories omitted from layers have the right permissions #1653

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[RFC] overlay: make sure directories omitted from layers have the right permissions #1653

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Commits on Jul 6, 2023

  1. aufs,overlay: backfill intermediate directories when possible 

    When extracting layer contents, if we find ourselves needing to
implicitly create a directory (due to its not being included in the
layer diff), try to give it the permissions, ownership, attributes, and
datestamp of the corresponding directory from the layer which would be
stacked below it.

When a layer omits any of the directories which contain items which that
layer adds or modifies, this should prevent the default values that we
would use from overriding those which correspond to the same directory
in a lower layer, which could later be mistaken as an indication that
one or more of those was intentionally changed, forcing the directory to
be pulled up.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>
    @nalind
    nalind committed Jul 6, 2023
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  2. chunked ApplyDiff(): track implicitly-created directories in layers 

    When applying a chunked diff, ApplyDiff() iterates through the entries
in the diff's table of contents, creating directories and other
zero-length items like empty files, symbolic links, and directories,
building a queue of hard links, and asking goroutines to locate files in
other layers and configured OSTree repositories which contain content
that matches what should eventually end up in non-zero-length files in
the layer.

If a file's entire contents couldn't be found locally, but it was split
into chunks in the chunked diff, ApplyDiff() then searches for the
chunks in local layers.

Lastly, the contents of files with non-zero lengths, which ApplyDiff()
had attempted to find locally, but which weren't found locally, are then
requested from the registry.

Track which directories in the layer are created implicitly by
ApplyDiff(), so that the overlay driver can reset their ownership,
permissions, extended attributes, and datestamps to match the
immediately lower layer, if there is one.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>
    @nalind
    nalind committed Jul 6, 2023
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