Merge branch 'eero/root-hash' into 'master'

Add target to print root files hash

Prints a hash of the files being included in rootfs. This will allow us to verify that rearrangement MRs have no real changes.

```
bazel run ic-os/<variant>/envs/<version>:echo-root-files-hash
``` 

See merge request dfinity-lab/public/ic!19222

ic-os/defs.bzl

@@ -8,7 +8,7 @@ load("//bazel:output_files.bzl", "output_files")
 load("//gitlab-ci/src/artifacts:upload.bzl", "upload_artifacts")
 load("//ic-os/bootloader:defs.bzl", "build_grub_partition")
 load("//ic-os/rootfs:boundary-guestos.bzl", boundary_rootfs_files = "rootfs_files")
-load("//toolchains/sysimage:toolchain.bzl", "build_container_base_image", "build_container_filesystem", "disk_image", "ext4_image", "inject_files", "sha256sum", "tar_extract", "upgrade_image")
+load("//toolchains/sysimage:toolchain.bzl", "build_container_base_image", "build_container_filesystem", "disk_image", "ext4_image", "inject_files", "sha256sum", "tar_extract", "tree_hash", "upgrade_image")
 
 def icos_build(
         name,
@@ -118,6 +118,31 @@ def icos_build(
         tags = ["manual"],
     )
 
+    # Helpful tool to print a hash of all input rootfs files
+    tree_hash(
+        name = "root-files-hash",
+        src = image_deps["rootfs_files"],
+        tags = ["manual"],
+    )
+
+    native.genrule(
+        name = "echo-root-files-hash",
+        srcs = [
+            ":root-files-hash",
+        ],
+        outs = ["root-files-hash-script"],
+        cmd = """
+        HASH="$(location :root-files-hash)"
+        cat <<EOF > $@
+#!/usr/bin/env bash
+set -euo pipefail
+cat $$HASH
+EOF
+        """,
+        executable = True,
+        tags = ["manual"],
+    )
+
     # -------------------- Extract root partition --------------------
 
     ext4_image(

toolchains/sysimage/toolchain.bzl

@@ -618,3 +618,28 @@ sha256sum = rule(
         ),
     },
 )
+
+def _tree_hash_impl(ctx):
+    out = ctx.actions.declare_file(ctx.label.name)
+    input_paths = []
+    for src in sorted(ctx.attr.src.items(), key = lambda v: v[1]):
+        input_paths.append(src[0].files.to_list()[0].path)
+    input_paths = " ".join(input_paths)
+
+    ctx.actions.run_shell(
+        inputs = ctx.files.src,
+        outputs = [out],
+        command = "cat {} | sha256sum | sed -e 's/ \\+-//' > {}".format(input_paths, out.path),
+    )
+
+    return [DefaultInfo(files = depset([out]), runfiles = ctx.runfiles([out]))]
+
+tree_hash = rule(
+    implementation = _tree_hash_impl,
+    attrs = {
+        "src": attr.label_keyed_string_dict(
+            allow_files = True,
+            mandatory = True,
+        ),
+    },
+)