rootfs: Mount tmpfs at /tmp during boot

[pulehui]

Mount tmpfs at /tmp during boot to keep bpf selftests temporary files in RAM and avoid writing them to the underlying root filesystem.

[pulehui]

@theihor @mykyta5 Hi all, not sure how to make review request in github, is this commit looks proper?

[theihor]

@pulehui we don't use rootfs code on BPF CI. Are you using this yourself?

[pulehui]

Hi @theihor,

I'm referring to tools/testing/selftests/bpf/vmtest.sh in the kernel tree, which downloads the prebuilt rootfs images referenced by INDEX in this repository.

IIUC, those rootfs images are generated from the scripts under rootfs/ here. Currently, when running tests via vmtest.sh, /tmp is not mounted as tmpfs, so temporary test artifacts are written directly to the root filesystem image.

[theihor]

Wow, I wasn't aware of that. Ok, let's merge this then.

But also the vmtest.sh needs to be fixed up to use the main branch (not master).
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/vmtest.sh#n68

Can you send a patch upstream?

[pulehui]

Wow, I wasn't aware of that. Ok, let's merge this then.

But also the vmtest.sh needs to be fixed up to use the main branch (not master). https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/vmtest.sh#n68

Can you send a patch upstream?

OK, will handle this