stages: replace "logger" binary in the dracut chroot

This commit replaces the `/usr/bin/logger` binary in the dracut
chroot with a bind mount to `/usr/bin/true` to silence the spam
that we get from dracut during initramfs generation:
```
logger: socket /dev/log: No such file or directory
```

Unfortunately I could not find a nicer way, it seems it is
not possible to simply pass `sysloglvl=0` via the commandline
or an environment.

The extra complication here is that the dracut stage mounts
`devtmpfs` which will likely include:
```
/dev/log -> /run/systemd/journal/dev-log
```
but of course inside this chroot there is no `/run` which
leads to these messages.

Closes: https://github.com/osbuild/osbuild/issues/1976

stages/org.osbuild.dracut

@@ -1,4 +1,8 @@
 #!/usr/bin/python3
+import contextlib
+import os
+import os.path
+import subprocess
 import sys
 
 import osbuild.api
@@ -10,6 +14,22 @@ def yesno(name: str, value: bool) -> str:
     return f"--{prefix}{name}"
 
 
+@contextlib.contextmanager
+def bind_mount_logger(tree: str) -> None:
+    logger_tree_path = os.path.join(tree, "usr/bin/logger")
+    if not os.path.exists(logger_tree_path):
+        # no logger -> nothing to do
+        yield
+        return
+    # make logger a "noop"
+    true_tree_path = os.path.join(tree, "usr/bin/true")
+    subprocess.run(["mount", "--rbind", true_tree_path, logger_tree_path], check=True)
+    try:
+        yield
+    finally:
+        subprocess.run(["umount", logger_tree_path], check=False)
+
+
 # pylint: disable=too-many-branches
 def main(tree, options):
     kernels = options["kernel"]
@@ -82,8 +102,15 @@ def main(tree, options):
         if initoverlayfs:
             initfs_bin = "/usr/bin/initoverlayfs-install"
 
-        with Chroot(tree) as chroot:
+        # the chroot.run() call below will mount /dev with "devtmpfs", this
-            chroot.run([initfs_bin, "--no-hostonly", "--kver", kver] + opts, check=True)
+        # is needed, see pr #1846 but it means we have likely have a
+        #   /dev/log -> /run/systemd/journal/dev-log
+        # symlink and dracut will try to log on it but end up writing
+        # 5k of "logger: socket /dev/log: No such file or directory"
+        # messages. See also issue #1976
+        with bind_mount_logger(tree):
+            with Chroot(tree) as chroot:
+                chroot.run([initfs_bin, "--no-hostonly", "--kver", kver] + opts, check=True)
 
     return 0
 

stages/test/test_dracut.py

@@ -29,3 +29,31 @@ def test_dracut_with_initoverlayfs(mocked_run, tmp_path, stage_module, with_init
     run_argv = args[0]
     assert run_argv[0] == "chroot"
     assert run_argv[2] == expected_argv2
+
+
+@patch("subprocess.run")
+def test_dracut_logger(mocked_run, tmp_path, stage_module):
+    fake_logger_path = tmp_path / "usr/bin/logger"
+    fake_logger_path.parent.mkdir(parents=True)
+    fake_logger_path.write_text("")
+    fake_true_path = tmp_path / "usr/bin/true"
+    fake_true_path.write_text("")
+
+    options = {
+        "kernel": [
+            "5.14.0-247.el9.x86_64",
+        ]
+    }
+    stage_module.main(tmp_path.as_posix(), options)
+    assert len(mocked_run.call_args_list) == 9
+    args, kwargs = mocked_run.call_args_list[0]  # bind-mount is the 1th call
+    assert kwargs.get("check") is True
+    run_argv = args[0]
+    assert run_argv == [
+        "mount", "--rbind",
+        fake_true_path.as_posix(), fake_logger_path.as_posix(),
+    ]
+    args, kwargs = mocked_run.call_args_list[8]  # umount is the 9th call
+    assert kwargs.get("check") is False
+    run_argv = args[0]
+    assert run_argv == ["umount", fake_logger_path.as_posix()]