acfc5f6d71
This disables buffering for the standard output stream for python
executables spawn within the build root. This should help with
the ordering of text output in stages: when stdout is buffered,
debug messages via `print` will be end up in that buffer. When
executables are run in the stage, via `subprocess.run` their
stdout has its own buffering, which will be flushed at the end
of the run. If stdout was not manually flushed before invoking
the executable, the output of the tool will be emitted before
anything in the buffer. For example:
print("stage")
subprocess.run(["echo", "tool"])
Will lead have the following ordering:
"tool"
"stage"
To avoid this, without having to manually flush the stdout
buffer before every `subprocess.run`, disable buffering for
python binaries run inside the build root.
260 lines
9.1 KiB
Python
260 lines
9.1 KiB
Python
"""Build Roots
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This implements the file-system environment available to osbuild modules. It
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uses `bubblewrap` to contain osbuild modules in a private environment with as
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little access to the outside as possible.
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"""
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import contextlib
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import importlib
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import importlib.util
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import io
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import os
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import stat
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import subprocess
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import tempfile
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__all__ = [
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"BuildRoot",
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]
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class CompletedBuild:
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"""The result of a `BuildRoot.run`
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Contains the actual `process` that was executed but also has
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convenience properties to quickly access the `returncode` and
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`output`. The latter is also provided via `stderr`, `stdout`
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properties, making it a drop-in replacement for `CompletedProcess`.
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"""
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def __init__(self, proc: subprocess.CompletedProcess, output: str):
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self.process = proc
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self.output = output
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@property
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def returncode(self):
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return self.process.returncode
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@property
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def stdout(self):
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return self.output
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@property
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def stderr(self):
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return self.output
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# pylint: disable=too-many-instance-attributes
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class BuildRoot(contextlib.AbstractContextManager):
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"""Build Root
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This class implements a context-manager that maintains a root file-system
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for contained environments. When entering the context, the required
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file-system setup is performed, and it is automatically torn down when
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exiting.
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The `run()` method allows running applications in this environment. Some
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state is persistent across runs, including data in `/var`. It is deleted
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only when exiting the context manager.
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"""
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def __init__(self, root, runner, libdir, var, *, rundir="/run/osbuild"):
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self._exitstack = None
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self._rootdir = root
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self._rundir = rundir
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self._vardir = var
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self._libdir = libdir
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self._runner = runner
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self._apis = []
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self.dev = None
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self.var = None
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@staticmethod
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def _mknod(path, name, mode, major, minor):
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os.mknod(os.path.join(path, name),
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mode=(stat.S_IMODE(mode) | stat.S_IFCHR),
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device=os.makedev(major, minor))
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def __enter__(self):
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self._exitstack = contextlib.ExitStack()
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with self._exitstack:
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# We create almost everything directly in the container as temporary
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# directories and mounts. However, for some things we need external
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# setup. For these, we create temporary directories which are then
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# bind-mounted into the container.
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#
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# For now, this includes:
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#
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# * We create a tmpfs instance *without* `nodev` which we then use
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# as `/dev` in the container. This is required for the container
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# to create device nodes for loop-devices.
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#
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# * We create a temporary directory for variable data and then use
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# it as '/var' in the container. This allows the container to
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# create throw-away data that it does not want to put into a
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# tmpfs.
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os.makedirs(self._rundir, exist_ok=True)
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dev = tempfile.TemporaryDirectory(prefix="osbuild-dev-", dir=self._rundir)
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self.dev = self._exitstack.enter_context(dev)
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os.makedirs(self._vardir, exist_ok=True)
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var = tempfile.TemporaryDirectory(prefix="osbuild-var-", dir=self._vardir)
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self.var = self._exitstack.enter_context(var)
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subprocess.run(["mount", "-t", "tmpfs", "-o", "nosuid", "none", self.dev], check=True)
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self._exitstack.callback(lambda: subprocess.run(["umount", "--lazy", self.dev], check=True))
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self._mknod(self.dev, "full", 0o666, 1, 7)
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self._mknod(self.dev, "null", 0o666, 1, 3)
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self._mknod(self.dev, "random", 0o666, 1, 8)
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self._mknod(self.dev, "urandom", 0o666, 1, 9)
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self._mknod(self.dev, "tty", 0o666, 5, 0)
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self._mknod(self.dev, "zero", 0o666, 1, 5)
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# Prepare all registered API endpoints
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for api in self._apis:
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self._exitstack.enter_context(api)
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self._exitstack = self._exitstack.pop_all()
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return self
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def __exit__(self, exc_type, exc_value, exc_tb):
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self._exitstack.close()
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self._exitstack = None
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def register_api(self, api: "BaseAPI"):
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"""Register an API endpoint.
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The context of the API endpoint will be bound to the context of
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this `BuildRoot`.
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"""
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self._apis.append(api)
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if self._exitstack:
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self._exitstack.enter_context(api)
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def run(self, argv, monitor, binds=None, readonly_binds=None):
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"""Runs a command in the buildroot.
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Takes the command and arguments, as well as bind mounts to mirror
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in the build-root for this command.
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This must be called from within an active context of this buildroot
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context-manager.
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Returns a `CompletedBuild` object.
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"""
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if not self._exitstack:
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raise RuntimeError("No active context")
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mounts = []
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# Import directories from the caller-provided root.
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for p in ["boot", "usr"]:
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source = os.path.join(self._rootdir, p)
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if os.path.isdir(source) and not os.path.islink(source):
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mounts += ["--ro-bind", source, os.path.join("/", p)]
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# Create /usr symlinks.
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mounts += ["--symlink", "usr/lib", "/lib"]
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mounts += ["--symlink", "usr/lib64", "/lib64"]
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mounts += ["--symlink", "usr/bin", "/bin"]
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mounts += ["--symlink", "usr/sbin", "/sbin"]
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# Setup /dev.
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mounts += ["--dev-bind", self.dev, "/dev"]
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mounts += ["--tmpfs", "/dev/shm"]
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# Setup temporary/data file-systems.
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mounts += ["--dir", "/etc"]
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mounts += ["--tmpfs", "/run"]
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mounts += ["--tmpfs", "/tmp"]
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mounts += ["--bind", self.var, "/var"]
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# Setup API file-systems.
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mounts += ["--proc", "/proc"]
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mounts += ["--bind", "/sys", "/sys"]
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mounts += ["--ro-bind-try", "/sys/fs/selinux", "/sys/fs/selinux"]
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# There was a bug in mke2fs (fixed in versionv 1.45.7) where mkfs.ext4
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# would fail because the default config, created on the fly, would
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# contain a syntax error. Therefore we bind mount the config from
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# the build root, if it exists
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mounts += ["--ro-bind-try",
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os.path.join(self._rootdir, "etc/mke2fs.conf"),
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"/etc/mke2fs.conf"]
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# We execute our own modules by bind-mounting them from the host into
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# the build-root. We have minimal requirements on the build-root, so
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# these modules can be executed. Everything else we provide ourselves.
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# In case `libdir` contains the python module, it must be self-contained
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# and we provide nothing else. Otherwise, we additionally look for
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# the installed `osbuild` module and bind-mount it as well.
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mounts += ["--ro-bind", f"{self._libdir}", "/run/osbuild/lib"]
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if not os.listdir(os.path.join(self._libdir, "osbuild")):
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modorigin = importlib.util.find_spec("osbuild").origin
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modpath = os.path.dirname(modorigin)
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mounts += ["--ro-bind", f"{modpath}", "/run/osbuild/lib/osbuild"]
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# Make caller-provided mounts available as well.
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for b in binds or []:
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mounts += ["--bind"] + b.split(":")
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for b in readonly_binds or []:
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mounts += ["--ro-bind"] + b.split(":")
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# Prepare all registered API endpoints: bind mount the address with
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# the `endpoint` name, provided by the API, into the well known path
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mounts += ["--dir", "/run/osbuild/api"]
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for api in self._apis:
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api_path = "/run/osbuild/api/" + api.endpoint
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mounts += ["--bind", api.socket_address, api_path]
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cmd = [
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"bwrap",
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"--cap-add", "CAP_MAC_ADMIN",
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"--chdir", "/",
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"--die-with-parent",
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"--new-session",
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"--setenv", "PATH", "/usr/sbin:/usr/bin",
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"--setenv", "PYTHONPATH", "/run/osbuild/lib",
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"--setenv", "PYTHONUNBUFFERED", "1",
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"--unshare-ipc",
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"--unshare-pid",
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"--unshare-net"
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]
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cmd += mounts
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cmd += ["--", f"/run/osbuild/lib/runners/{self._runner}"]
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cmd += argv
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proc = subprocess.Popen(cmd,
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bufsize=0,
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stdin=subprocess.DEVNULL,
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stdout=subprocess.PIPE,
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stderr=subprocess.STDOUT,
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close_fds=True)
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data = io.StringIO()
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fd = proc.stdout.fileno()
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while True:
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buf = os.read(fd, 32768)
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if not buf:
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break
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txt = buf.decode("utf-8")
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data.write(txt)
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monitor.log(txt)
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buf, _ = proc.communicate()
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txt = buf.decode("utf-8")
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monitor.log(txt)
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data.write(txt)
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output = data.getvalue()
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data.close()
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return CompletedBuild(proc, output)
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