On 2023/5/26 10:27, Gao Xiang wrote:
Hi Giuseppe,
On 2023/5/26 09:59, Giuseppe Scrivano wrote:
Hi Amir,
Amir Goldstein <amir73il@xxxxxxxxx> writes:
On Thu, May 25, 2023 at 6:21 PM Alexander Larsson <alexl@xxxxxxxxxx> wrote:
Something that came up about this in a discussion recently was
multi-layer composefs style images. For example, this may be a useful
approach for multi-layer container images.
In such a setup you would have one lowerdata layer, but two real
lowerdirs, like lowerdir=A:B::C. In this situation a file in B may
accidentally have the same name as a file on C, causing a redirect
from A to end up in B instead of C.
I was under the impression that the names of the data blobs in C
are supposed to be content derived names (hash).
Is this not the case or is the concern about hash conflicts?
Would it be possible to have a syntax for redirects that mean "only
lookup in lowerdata layers. For example a double-slash path
//some/file.
Anything is possible if we can define the problem that needs to be solved.
In this case, I did not understand why the problem is limited to finding a file
by mistake in layer B.
If there are several data layers A:B::C:D why wouldn't we have the same
problem with a file name collision between C and D?
the data layer is constructed in a way that files are stored by their
hash and there is control from the container runtime on how this is
built and maintained. So a file name collision would happen only when
on a hash collision.
Differently for the other layers we've no control on what files are in
the image, unless we limit to mount only one EROFS as the first lower
layer and then all the other lower layers are data layers.
Given your example above A:B::C:D, if both A and B are EROFS we are
limited in the files/directories that can be in B.
If my understanding is correct (hopefully), I might ask if it's the
proposal to pass in multiple composefs manifests (rather than one)
all together to overlayfs in one shot?
Oh I could see the issue if a composefs manifest works with other
regular underlay layers, such redirect might need a way directly
to data layers instead of any potential underlay layer.
