Skopeo support for BigFilesTemporaryDir (SystemContext)

[malaiwah]

I am using Skopeo to export docker-daemon images to docker-archive format and I find the tool really useful but it seems there is no way to define the temporary directory (it does not honour the TMPDIR environment variable) for the temporary copies made. It defaults to /var/tmp, which on the systems I use is quite tight.

There is a way to instruct containers/image to use a different folder for temporary files, but the option is not exposed thru the skopeo cli with an --option. The SystemContext field is called BigFilesTemporaryDir .

Here is where it is set for its default: https://github.com/containers/image/blob/de5ad242e515688f69225ca6d897cfb221e0f5c7/internal/tmpdir/tmpdir.go#L18

Here is where the copy operation fails on my system: https://github.com/containers/image/blob/d13a90f787a7d3cd58e6f13c7cd1f2307b74a1ef/docker/tarfile/dest.go#L110

Here is the pull request for BigFilesTemporaryDir: containers/image#747

[malaiwah]

It might be easy to put it right here:

skopeo/cmd/skopeo/utils.go

Line 128 in 4489ddd

func imageFlags(global *globalOptions, shared *sharedImageOptions, flagPrefix, credsOptionAlias string) ([]cli.Flag, *imageOptions) {

and

skopeo/cmd/skopeo/utils.go

Line 147 in 4489ddd

func (opts *imageOptions) newSystemContext() (*types.SystemContext, error) {

and I might take a try at it.

[rhatdan]

We are using this on Buildah now, but we should expose this or at least allow the setting of TMPDIR to modify the setting.

[mtrmac]

#868 was merged.