[antlir2][container subtarget] add option to run alternate binary

Summary:
Title.

While I'm here, rename `nspawn` to `container` since we're going to move off of
nspawn soon, and because the name of the target is `[container]`

Test Plan:
```
❯ buck2 run fbcode//antlir/antlir2/test_images/rpms:simple--layer[container] -- -- echo foo
Buck UI: https://www.internalfb.com/buck2/c288fde3-997c-4906-90e0-2a3596eeaf0f
Network: Up: 13KiB  Down: 542B  (reSessionID-c5e70c49-a5d1-4fe1-ac8b-4cdf2228c5b7)
Jobs completed: 158119. Time elapsed: 27.4s.
Cache hits: 0%. Commands: 1 (cached: 0, remote: 0, local: 1)
BUILD SUCCEEDED
foo
```

Reviewed By: sergeyfd

Differential Revision: D50121508

fbshipit-source-id: 0bd7e8f00fa4e6f07e8cd45731c62fcba9692349

antlir/antlir2/bzl/image/layer.bzl

@@ -25,7 +25,7 @@ load("//antlir/rpm/dnf2buck:repo.bzl", "RepoInfo", "RepoSetInfo")
 load("//antlir/bzl/build_defs.bzl", "config", "get_visibility")
 load(":cfg.bzl", "layer_cfg")
 load(":depgraph.bzl", "build_depgraph")
-load(":mounts.bzl", "all_mounts", "nspawn_mount_args")
+load(":mounts.bzl", "all_mounts", "container_mount_args")
 
 def _map_image(
         ctx: AnalysisContext,
@@ -69,7 +69,7 @@ def _map_image(
 
     return cmd, out
 
-def _nspawn_sub_target(nspawn_binary: Dependency, subvol: Artifact, mounts: list[mount_record]) -> list[Provider]:
+def _container_sub_target(binary: Dependency, subvol: Artifact, mounts: list[mount_record]) -> list[Provider]:
     dev_mode_args = cmd_args()
     if REPO_CFG.artifacts_require_repo:
         dev_mode_args = cmd_args(
@@ -80,9 +80,9 @@ def _nspawn_sub_target(nspawn_binary: Dependency, subvol: Artifact, mounts: list
         DefaultInfo(),
         RunInfo(cmd_args(
             "sudo",
-            nspawn_binary[RunInfo],
+            binary[RunInfo],
             cmd_args(subvol, format = "--subvol={}"),
-            cmd_args([nspawn_mount_args(mount) for mount in mounts]),
+            cmd_args([container_mount_args(mount) for mount in mounts]),
             dev_mode_args,
         )),
     ]
@@ -393,7 +393,7 @@ def _impl_with_features(features: ProviderCollection, *, ctx: AnalysisContext) -
             DefaultInfo(
                 sub_targets = {
                     "build": [DefaultInfo(build_script), RunInfo(cmd_args(build_script))],
-                    "container": _nspawn_sub_target(ctx.attrs._run_nspawn, final_subvol, mounts = phase_mounts),
+                    "container": _container_sub_target(ctx.attrs._run_container, final_subvol, mounts = phase_mounts),
                     "features": [DefaultInfo(features_json_artifact)],
                     "logs": [DefaultInfo(all_logs, sub_targets = {
                         key: [DefaultInfo(artifact)]
@@ -420,7 +420,7 @@ def _impl_with_features(features: ProviderCollection, *, ctx: AnalysisContext) -
     mounts = all_mounts(features = all_features, parent_layer = parent_layer_info)
     # @oss-disable
 
-    sub_targets["container"] = _nspawn_sub_target(ctx.attrs._run_nspawn, final_subvol, mounts)
+    sub_targets["container"] = _container_sub_target(ctx.attrs._run_container, final_subvol, mounts)
     sub_targets["debug"] = [DefaultInfo(sub_targets = debug_sub_targets)]
 
     providers = [
@@ -508,7 +508,7 @@ _layer_attrs = {
         default = None,
     ),
     "_objcopy": attrs.exec_dep(default = "fbsource//third-party/binutils:objcopy"),
-    "_run_nspawn": attrs.exec_dep(default = "//antlir/antlir2/nspawn_in_subvol:nspawn"),
+    "_run_container": attrs.exec_dep(default = "//antlir/antlir2/container_subtarget:run"),
     "_selected_target_arch": attrs.default_only(attrs.string(
         default = arch_select(aarch64 = "aarch64", x86_64 = "x86_64"),
         doc = "CPU arch that this layer is being built for. This is always " +

antlir/antlir2/bzl/image/mounts.bzl

@@ -54,7 +54,7 @@ def all_mounts(
 
     return mounts
 
-def nspawn_mount_args(mount: mount_record) -> cmd_args:
+def container_mount_args(mount: mount_record) -> cmd_args:
     if mount.layer:
         return cmd_args("--bind-mount-ro", mount.layer.src.subvol_symlink, mount.layer.mountpoint)
     elif mount.host:

antlir/antlir2/bzl/package/defs.bzl

@@ -23,7 +23,7 @@ _default_attrs = {
     "_antlir2_packager": attrs.default_only(attrs.exec_dep(default = "//antlir/antlir2/antlir2_packager:antlir2-packager")),
     "_dot_meta_feature": attrs.dep(default = "//antlir/antlir2/bzl/package:dot-meta"),
     "_objcopy": attrs.default_only(attrs.exec_dep(default = "fbsource//third-party/binutils:objcopy")),
-    "_run_nspawn": attrs.default_only(attrs.exec_dep(default = "//antlir/antlir2/nspawn_in_subvol:nspawn")),
+    "_run_container": attrs.exec_dep(default = "//antlir/antlir2/container_subtarget:run"),
     "_target_arch": attrs.default_only(attrs.string(
         default = arch_select(aarch64 = "aarch64", x86_64 = "x86_64"),
     )),
@@ -81,7 +81,7 @@ def _generic_impl(
             "_antlir2": ctx.attrs._antlir2,
             "_dot_meta_feature": ctx.attrs._dot_meta_feature,
             "_objcopy": ctx.attrs._objcopy,
-            "_run_nspawn": ctx.attrs._run_nspawn,
+            "_run_container": ctx.attrs._run_container,
             "_target_arch": ctx.attrs._target_arch,
         }, with_artifacts = True).promise.map(partial(
             _generic_impl_with_layer,

antlir/antlir2/bzl/package/stamp_buildinfo.bzl

@@ -16,7 +16,7 @@ def _impl(ctx: AnalysisContext) -> Promise:
         "target_arch": ctx.attrs._target_arch,
         "_feature_feature_targets": [ctx.attrs._dot_meta_feature],
         "_objcopy": ctx.attrs._objcopy,
-        "_run_nspawn": ctx.attrs._run_nspawn,
+        "_run_container": ctx.attrs._run_container,
         "_selected_target_arch": ctx.attrs._target_arch,
     }, with_artifacts = True).promise.map(lambda l: [l[LayerInfo], l[DefaultInfo]])
 
@@ -27,7 +27,7 @@ stamp_buildinfo_rule = rule(
                 "_antlir2": attrs.exec_dep(default = "//antlir/antlir2/antlir2:antlir2"),
                 "_dot_meta_feature": attrs.dep(default = "//antlir/antlir2/bzl/package:dot-meta"),
                 "_objcopy": attrs.default_only(attrs.exec_dep(default = "fbsource//third-party/binutils:objcopy")),
-                "_run_nspawn": attrs.default_only(attrs.exec_dep(default = "//antlir/antlir2/nspawn_in_subvol:nspawn")),
+                "_run_container": attrs.exec_dep(default = "//antlir/antlir2/container_subtarget:run"),
                 "_target_arch": attrs.default_only(attrs.string(
                     default = arch_select(aarch64 = "aarch64", x86_64 = "x86_64"),
                 )),

antlir/antlir2/nspawn_in_subvol/BUCK → antlir/antlir2/container_subtarget/BUCK

@@ -3,7 +3,7 @@ load("//antlir/bzl:build_defs.bzl", "rust_binary")
 oncall("twimage")
 
 rust_binary(
-    name = "nspawn",
+    name = "run",
     srcs = glob(["src/**/*.rs"]),
     visibility = ["PUBLIC"],
     deps = [

antlir/antlir2/nspawn_in_subvol/src/main.rs → antlir/antlir2/container_subtarget/src/main.rs

@@ -6,6 +6,7 @@
  */
 
 use std::collections::HashMap;
+use std::ffi::OsString;
 use std::os::unix::process::CommandExt;
 use std::path::PathBuf;
 
@@ -31,6 +32,8 @@ struct Args {
     /// `--user` run command as a given user
     #[clap(long, default_value = "root")]
     user: String,
+    #[clap(last = true)]
+    cmd: Vec<OsString>,
 }
 
 fn init_logging() {
@@ -76,8 +79,13 @@ fn main() -> anyhow::Result<()> {
         cmd_builder.inputs(repo_root.into_path_buf());
         cmd_builder.inputs(PathBuf::from("/usr/local/fbcode"));
     }
+
+    let mut cmd = args.cmd.into_iter();
+    let program = cmd.next().unwrap_or(OsString::from("/bin/bash"));
+
     Err(isolate(cmd_builder.build())?
-        .command("/bin/bash")?
+        .command(program)?
+        .args(cmd)
         .exec()
         .into())
 }