[antlir2][image_test] add hostname option

Summary: Small missing feature

Test Plan:
```
❯ buck2 test fbcode//antlir/antlir2/testing/tests:test-hostname fbcode//antlir/antlir2/testing/tests:test-hostname-booted
Buck UI: https://www.internalfb.com/buck2/cd5d357f-4089-45b9-a221-f827d14d229c
Test UI: https://www.internalfb.com/intern/testinfra/testrun/17169973583492924
Network: Up: 32MiB  Down: 209MiB  (reSessionID-8184c46f-74df-4daa-a8ba-2270c0d778ca)
Jobs completed: 267. Time elapsed: 1:05.6s.
Cache hits: 0%. Commands: 169 (cached: 0, remote: 1, local: 168). Fallback: 1/169
Tests finished: Pass 2. Fail 0. Fatal 0. Skip 0. Build failure 0
```

Reviewed By: r1mikey

Differential Revision: D49756197

fbshipit-source-id: d45001c530d6ed35e799660da373deaf5fa12551

antlir/antlir2/antlir2_isolate/src/lib.rs

@@ -62,6 +62,8 @@ pub struct IsolationContext<'a> {
     ephemeral: bool,
     /// See [IsolationContextBuilder::tmpfs]
     tmpfs: BTreeSet<Cow<'a, Path>>,
+    /// See [IsolationContextBuilder::hostname]
+    hostname: Option<Cow<'a, str>>,
 }
 
 /// Controls how the container is spawned and how console is configured for the
@@ -104,6 +106,7 @@ impl<'a> IsolationContext<'a> {
                 user: Cow::Borrowed("root"),
                 ephemeral: true,
                 tmpfs: Default::default(),
+                hostname: None,
             },
         }
     }
@@ -188,6 +191,12 @@ impl<'a> IsolationContextBuilder<'a> {
         self
     }
 
+    /// Set the hostname in the container
+    pub fn hostname<S: Into<Cow<'a, str>>>(&mut self, hostname: S) -> &mut Self {
+        self.ctx.hostname = Some(hostname.into());
+        self
+    }
+
     /// Finalize the IsolationContext
     pub fn build(&mut self) -> IsolationContext<'a> {
         self.ctx.clone()

antlir/antlir2/antlir2_isolate/src/sys/bwrap/mod.rs

@@ -39,6 +39,7 @@ pub fn bwrap(ctx: IsolationContext, bwrap: Option<&OsStr>) -> Result<IsolatedCon
         user,
         ephemeral,
         tmpfs,
+        hostname,
     } = ctx;
     assert_eq!(user, "root", "user != root unimplemented");
     assert!(!register, "register unimplemented");
@@ -67,7 +68,11 @@ pub fn bwrap(ctx: IsolationContext, bwrap: Option<&OsStr>) -> Result<IsolatedCon
     // detach from this process's controlling terminal
     bwrap_args.push("--new-session".into());
     bwrap_args.push("--hostname".into());
-    bwrap_args.push("antlir2".into());
+    if let Some(hostname) = hostname {
+        bwrap_args.push(hostname.as_ref().into());
+    } else {
+        bwrap_args.push(Uuid::new_v4().simple().to_string().into());
+    }
 
     // our containers are for isolation, not security, so having all the caps of
     // the parent is desirable when we need to do things like btrfs snapshots

antlir/antlir2/antlir2_isolate/src/sys/nspawn.rs

@@ -72,6 +72,7 @@ pub fn nspawn(ctx: IsolationContext) -> Result<IsolatedContext> {
         user,
         ephemeral,
         tmpfs,
+        hostname,
     } = ctx;
     let mut nspawn_args = Vec::<OsString>::new();
     let mut env = HashMap::new();
@@ -88,6 +89,10 @@ pub fn nspawn(ctx: IsolationContext) -> Result<IsolatedContext> {
     nspawn_args.push("--private-network".into());
     nspawn_args.push("--user".into());
     nspawn_args.push(user.as_ref().into());
+    if let Some(hostname) = hostname {
+        nspawn_args.push("--hostname".into());
+        nspawn_args.push(hostname.as_ref().into());
+    }
     // keep whatever timezone was in the image, not on the host
     nspawn_args.push("--timezone=off".into());
     // Don't pollute the host's /var/log/journal

antlir/antlir2/testing/image_test.bzl

@@ -33,6 +33,7 @@ def _impl(ctx: AnalysisContext) -> list[Provider]:
         ctx.attrs.image_test[RunInfo],
         cmd_args(ctx.attrs.layer[LayerInfo].subvol_symlink, format = "--layer={}"),
         cmd_args(ctx.attrs.run_as_user, format = "--user={}"),
+        cmd_args(ctx.attrs.hostname, format = "--hostname={}") if ctx.attrs.hostname else cmd_args(),
         cmd_args("--boot") if ctx.attrs.boot else cmd_args(),
         cmd_args(boot_requires_units, format = "--requires-unit={}") if ctx.attrs.boot else cmd_args(),
         cmd_args(boot_after_units, format = "--after-unit={}") if ctx.attrs.boot else cmd_args(),
@@ -93,6 +94,7 @@ _image_test = rule(
             default = None,
             doc = "Add a Requires= and After= requirement on these units to the test",
         ),
+        "hostname": attrs.option(attrs.string(), default = None),
         "image_test": attrs.default_only(attrs.exec_dep(default = "//antlir/antlir2/testing/image_test:image-test")),
         "labels": attrs.list(attrs.string(), default = []),
         "layer": attrs.dep(providers = [LayerInfo]),
@@ -116,6 +118,7 @@ def _implicit_image_test(
         boot: bool = False,
         boot_requires_units: [list[str], None] = None,
         boot_after_units: [list[str], None] = None,
+        hostname: str | None = None,
         _add_outer_labels: list[str] = [],
         **kwargs):
     test_rule(
@@ -152,6 +155,7 @@ def _implicit_image_test(
         boot = boot,
         boot_requires_units = boot_requires_units,
         boot_after_units = boot_after_units,
+        hostname = hostname,
     )
 
 image_cpp_test = partial(

antlir/antlir2/testing/image_test/src/main.rs

@@ -48,6 +48,9 @@ struct Args {
     /// Run the test as this user
     user: String,
     #[clap(long)]
+    /// Set container hostname
+    hostname: Option<String>,
+    #[clap(long)]
     /// Boot the container with /init as pid1 before running the test
     boot: bool,
     #[clap(long = "requires-unit", requires = "boot")]
@@ -148,6 +151,10 @@ fn main() -> Result<()> {
         ctx.outputs([Path::new("/dev/fuse")]);
     }
 
+    if let Some(hostname) = args.hostname {
+        ctx.hostname(hostname);
+    }
+
     if args.boot {
         let container_stdout = container_stdout_file()?;
         let (mut test_stdout, mut test_stderr) = make_log_files("test")?;

antlir/antlir2/testing/tests/BUCK

@@ -83,6 +83,21 @@ image.layer(
     ]
 ]
 
+image_python_test(
+    name = "test-hostname",
+    srcs = ["test_hostname.py"],
+    hostname = "antlir2-test-hostname",
+    layer = ":base",
+)
+
+image_python_test(
+    name = "test-hostname-booted",
+    srcs = ["test_hostname.py"],
+    boot = True,
+    hostname = "antlir2-test-hostname",
+    layer = ":base",
+)
+
 image.layer(
     name = "foo-rpms",
     dnf_available_repos = "//antlir/antlir2/test_images/rpms:test-repo-set",

antlir/antlir2/testing/tests/test_hostname.py

@@ -0,0 +1,15 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+import socket
+import unittest
+
+
+class TestHostname(unittest.TestCase):
+    def setUp(self) -> None:
+        super().setUp()
+
+    def test_hostname(self) -> None:
+        self.assertEqual(socket.gethostname(), "antlir2-test-hostname")