[antlir2][genrule_in_image] mount layer mounts at runtime

Summary:
When running a `genrule_in_image` command, properly mount in any
`feature.layer_mount`s into the container.

Test Plan:
```
❯ buck2 test fbcode//antlir/antlir2/genrule_in_image/tests:
Buck UI: https://www.internalfb.com/buck2/534e0055-501a-40c6-9922-ba02a3184b26
Test UI: https://www.internalfb.com/intern/testinfra/testrun/281475372326083
Tests finished: Pass 14. Fail 0. Fatal 0. Skip 0. Build failure 0
```

Reviewed By: epilatow

Differential Revision: D67343514

fbshipit-source-id: d30133d6573a574f9823e73de2cf5a2d5f5509a6

antlir/antlir2/genrule_in_image/genrule_in_image.bzl

@@ -10,6 +10,7 @@ load("//antlir/antlir2/bzl:selects.bzl", "selects")
 load("//antlir/antlir2/bzl:types.bzl", "LayerInfo")
 load("//antlir/antlir2/bzl/image:cfg.bzl", "attrs_selected_by_cfg", "cfg_attrs", "layer_cfg")
 load("//antlir/antlir2/bzl/image:layer.bzl", "layer_rule")
+load("//antlir/antlir2/bzl/image:mounts.bzl", "all_mounts", "container_mount_args")
 load("//antlir/antlir2/os:package.bzl", "get_default_os_for_package", "should_all_images_in_package_use_default_os")
 
 def _impl(ctx: AnalysisContext) -> list[Provider] | Promise:
@@ -53,6 +54,13 @@ def _impl(ctx: AnalysisContext) -> list[Provider] | Promise:
                 cmd_args(ctx.attrs._working_format, format = "--working-format={}"),
                 cmd_args(out.as_output(), format = "--out={}"),
                 "--dir" if out_is_dir else cmd_args(),
+                cmd_args([
+                    container_mount_args(mount)
+                    for mount in all_mounts(
+                        features = layer[LayerInfo].features,
+                        parent_layer = layer[LayerInfo].parent[LayerInfo] if layer[LayerInfo].parent else None,
+                    )
+                ]),
                 "--",
                 ctx.attrs.bash,
             ),

antlir/antlir2/genrule_in_image/src/main.rs

@@ -5,12 +5,14 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+use std::collections::HashMap;
 use std::path::Path;
 use std::path::PathBuf;
 
 use antlir2_isolate::unshare;
 use antlir2_isolate::IsolationContext;
 use antlir2_overlayfs::OverlayFs;
+use anyhow::anyhow;
 use anyhow::ensure;
 use anyhow::Context;
 use anyhow::Result;
@@ -28,6 +30,9 @@ struct Args {
     #[clap(value_enum, long)]
     /// On-disk format of the layer storage
     working_format: WorkingFormat,
+    /// `--bind-mount-ro src dst` creates an RO bind-mount of src to dst in the subvol
+    #[clap(long, num_args = 2)]
+    bind_mount_ro: Vec<PathBuf>,
     #[clap(flatten)]
     out: Out,
     #[clap(last(true))]
@@ -98,6 +103,16 @@ fn main() -> Result<()> {
         .tmpfs(Path::new("/tmp"))
         .devtmpfs(Path::new("/dev"));
 
+    builder.inputs(
+        args.bind_mount_ro
+            .chunks(2)
+            .map(|pair| match pair {
+                [src, dst] => Ok((dst.clone(), src.clone())),
+                _ => Err(anyhow!("Unrecognized mount arg: {:?}", pair)),
+            })
+            .collect::<anyhow::Result<HashMap<_, _>>>()?,
+    );
+
     if args.out.dir {
         std::fs::create_dir_all(&args.out.out)?;
         builder

antlir/antlir2/genrule_in_image/tests/BUCK

@@ -132,6 +132,42 @@ genrule_in_image(
     layer = ":with-par",
 )
 
+image.layer(
+    name = "mount-src",
+    features = [
+        feature.install_text(
+            dst = "/file-in-mount-1",
+            text = "file 1 in mounted layer",
+        ),
+        feature.install_text(
+            dst = "/file-in-mount-2",
+            text = "file 2 in mounted layer",
+        ),
+    ],
+)
+
+image.layer(
+    name = "layer-with-mount",
+    features = [
+        feature.ensure_dirs_exist(dirs = "/mnt/layer"),
+        feature.layer_mount(
+            mountpoint = "/mnt/layer",
+            source = ":mount-src",
+        ),
+    ],
+    parent_layer = ":layer",
+)
+
+genrule_in_image(
+    name = "with-mount",
+    out = "f",
+    bash = """
+        ls /mnt/layer > $OUT
+        cat /mnt/layer/file-in-mount-1 >> $OUT
+    """,
+    layer = ":layer-with-mount",
+)
+
 python_unittest(
     name = "test",
     srcs = ["test.py"],
@@ -144,5 +180,6 @@ python_unittest(
         "NAMED_DIR": "$(location :named-dir)",
         "NAMED_OUTS": "$(location :named-outs)",
         "SINGLE_FILE": "$(location :single-file)",
+        "WITH_MOUNT": "$(location :with-mount)",
     },
 )

antlir/antlir2/genrule_in_image/tests/test.py

@@ -52,3 +52,10 @@ def test_installed_par(self) -> None:
         f = Path(os.getenv("INSTALLED_PAR"))
         self.assertTrue(f.exists())
         self.assertEqual(f.read_text(), "From par\n")
+
+    def test_with_mount(self) -> None:
+        f = Path(os.getenv("WITH_MOUNT"))
+        self.assertTrue(f.exists())
+        self.assertEqual(
+            f.read_text(), "file-in-mount-1\nfile-in-mount-2\nfile 1 in mounted layer"
+        )