Overlay layer limit lower for non-rootfs mounts

[tonistiigi]

With a Dockerfile like https://gist.github.com/tonistiigi/d713961d895b36a756bfcec160e710c1 I can have a base stage containing 100+ layers (historic limit is set to 127) without any issues. But when the same stage is mounted to another stage via RUN --mount=from=base,, then the base stage can only have a maximum of 70 layers before it starts to error. The number of layers seems to depend on the storage path length so probably related to the page size limit of mount options.

Error:

> [linux/arm64] generating sbom using [docker.io/docker/buildkit-syft-scanner:stable-1](http://docker.io/docker/buildkit-syft-scanner:stable-1):
0.027 runc run failed: unable to start container process: error during container init: error mounting “overlay” to rootfs at “/run/src/core/sbom”: mount overlay:/run/src/core/sbom (via /proc/self/fd/6), data: index=off,lowerdir=/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/140/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/139/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/138/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/137/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/136/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/135/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/134/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/133/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/132/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/131/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/130/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/129/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/128/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/127/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/69/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/68/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/67/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/66/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/65/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/64/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/63/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/62/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/61/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/60/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/59/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/56/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/55/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/54/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/53/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/52/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/51/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/50/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/49/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/48/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/47/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/46/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/45/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/44/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/43/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/42/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/41/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/40/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/39/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/38/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/37/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/36/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/35/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/34/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/33/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/32/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/31/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/30/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/29/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/28/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/27/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/26/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/25/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/24/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/23/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/22/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/21/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/20/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/18/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/17/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/16/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/15/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/14/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/13/fs:/var/lib/buildkit/runc-overlayfs/snapshots/snapshots/9/fs,redirect_dir=off: no such file or directory

In another similar report (with different storage path) the error happened on the same mount but was too many levels of symbolic links.