Re: [PATCH bpf-next v3 2/4] libfs: support RENAME_EXCHANGE in simple_rename()

On Tue, Nov 02, 2021 at 11:11:02AM +0100, Daniel Borkmann wrote:

On 11/2/21 10:25 AM, Miklos Szeredi wrote:

quoted

On Thu, 28 Oct 2021 at 11:48, Lorenz Bauer [off-list ref] wrote:

quoted

Allow atomic exchange via RENAME_EXCHANGE when using simple_rename.
This affects binderfs, ramfs, hubetlbfs and bpffs.

Ramfs and hugetlbfs are generic enough; those seem safe.

Binderfs: I have no idea what this does; binderfs_rename() should

Fwiw, allows dynamic creation and removal of Android binder ipc
devices. Each mount is a separate instance and it's mountable inside
unprivileged containers. Since Android 12 default how binder devices are
managed. Also makes it possibe to run Android in unprivileged
containers.

quoted

probably error out on RENAME_EXCHANGE for now, or an explicit ack from
the maintainers.

Thanks for the review, Miklos! Adding Christian to Cc wrt binderfs ... full context
for all patches: https://lore.kernel.org/bpf/20211028094724.59043-1-lmb@cloudflare.com/ (local)

Yep, I saw that. Seems good.

probably error out on RENAME_EXCHANGE for now, or an explicit ack from
the maintainers.

I don't think there is any issue in allowing binderfs to support this.
Binderfs files are always device nodes. Allowing them to be atomically
renamed shouldn't be a problem. So:

Acked-by: Christian Brauner <redacted>

Christian