[chandarith-chea]

Problem

On Dockiva 0.6.10:

docker --context dockiva run --rm -v somevol:/v alpine sh -c 'echo x > /v/a; ln /v/a /v/b'
ln: /v/b: No such file or directory

Linux makes the link. The same call in the container's own layer worked.

Cause

linkat in native/fs.h refused a source the walk found in neither image layer (old.layer==2) with ENOENT before asking the host. For a leaf inside a bind mount, ov_walk leaves ov_leaf.layer at 2 and ov_leaf.canon empty, because the layers do not apply there. So every source in a mount counted as missing whenever the container had image layers.

Fix

One condition: the check applies only when old.canon[0] is set (a leaf in the layers). In a mount the host's linkat reports a missing source. The neighbouring ov_prepare and ov_created calls already return early for an empty canon, and EXDEV across a mount boundary is decided earlier from the two paths' mounts, unchanged.

Test

tests/native/mountlink_guest.c, run by scripts/verify_overlay.py on every built runtime, with and without the memory layer (--lower, --root, --bind at /vol and /vol2):

• a link inside the mount shares the source's inode (absolute path, descriptor of the mount's directory, symlink with AT_SYMLINK_FOLLOW)
• missing source is ENOENT, taken name is EEXIST
• a link to another mount, or to or from the layers (image file, new file), is EXDEV
• an image file is still linked in the layers (copy-up); a missing layer source is still ENOENT
• the verifier then checks the host directories: one inode under three names, nothing in the second mount

On origin/main the guest fails at the first in-mount link on all 8 runs.

Checks run locally

• scripts/verify_overlay.py: 53/53 (4 runtime builds)
• scripts/verify_fork_sockets.py: 100/100, twice. One earlier run failed hvf sleeper_guest --cpus 2 (a latency check) with the Mac at load 13; standalone it passes 6/6 on this branch and on origin/main.

Not checked: a bundle built from this branch with the docker run -v command above.

Note for #34

tests/native/rootdac_guest.c there makes hard links only in /w because of this bug. This branch touches scripts/verify_overlay.py at different places than #34 (no textual overlap expected).