diff options
Diffstat (limited to 'nixos/modules/system/etc/build-composefs-dump.py')
-rw-r--r-- | nixos/modules/system/etc/build-composefs-dump.py | 209 |
1 files changed, 209 insertions, 0 deletions
diff --git a/nixos/modules/system/etc/build-composefs-dump.py b/nixos/modules/system/etc/build-composefs-dump.py new file mode 100644 index 000000000000..923d40008b63 --- /dev/null +++ b/nixos/modules/system/etc/build-composefs-dump.py @@ -0,0 +1,209 @@ +#!/usr/bin/env python3 + +"""Build a composefs dump from a Json config + +See the man page of composefs-dump for details about the format: +https://github.com/containers/composefs/blob/main/man/composefs-dump.md + +Ensure to check the file with the check script when you make changes to it: + +./check-build-composefs-dump.sh ./build-composefs_dump.py +""" + +import glob +import json +import os +import sys +from enum import Enum +from pathlib import Path +from typing import Any + +Attrs = dict[str, Any] + + +class FileType(Enum): + """The filetype as defined by the `st_mode` stat field in octal + + You can check the st_mode stat field of a path in Python with + `oct(os.stat("/path/").st_mode)` + """ + + directory = "4" + file = "10" + symlink = "12" + + +class ComposefsPath: + path: str + size: int + filetype: FileType + mode: str + uid: str + gid: str + payload: str + rdev: str = "0" + nlink: int = 1 + mtime: str = "1.0" + content: str = "-" + digest: str = "-" + + def __init__( + self, + attrs: Attrs, + size: int, + filetype: FileType, + mode: str, + payload: str, + path: str | None = None, + ): + if path is None: + path = attrs["target"] + self.path = "/" + path + self.size = size + self.filetype = filetype + self.mode = mode + self.uid = attrs["uid"] + self.gid = attrs["gid"] + self.payload = payload + + def write_line(self) -> str: + line_list = [ + str(self.path), + str(self.size), + f"{self.filetype.value}{self.mode}", + str(self.nlink), + str(self.uid), + str(self.gid), + str(self.rdev), + str(self.mtime), + str(self.payload), + str(self.content), + str(self.digest), + ] + return " ".join(line_list) + + +def eprint(*args, **kwargs) -> None: + print(args, **kwargs, file=sys.stderr) + + +def leading_directories(path: str) -> list[str]: + """Return the leading directories of path + + Given the path "alsa/conf.d/50-pipewire.conf", for example, this function + returns `[ "alsa", "alsa/conf.d" ]`. + """ + parents = list(Path(path).parents) + parents.reverse() + # remove the implicit `.` from the start of a relative path or `/` from an + # absolute path + del parents[0] + return [str(i) for i in parents] + + +def add_leading_directories( + target: str, attrs: Attrs, paths: dict[str, ComposefsPath] +) -> None: + """Add the leading directories of a target path to the composefs paths + + mkcomposefs expects that all leading directories are explicitly listed in + the dump file. Given the path "alsa/conf.d/50-pipewire.conf", for example, + this function adds "alsa" and "alsa/conf.d" to the composefs paths. + """ + path_components = leading_directories(target) + for component in path_components: + composefs_path = ComposefsPath( + attrs, + path=component, + size=4096, + filetype=FileType.directory, + mode="0755", + payload="-", + ) + paths[component] = composefs_path + + +def main() -> None: + """Build a composefs dump from a Json config + + This config describes the files that the final composefs image is supposed + to contain. + """ + config_file = sys.argv[1] + if not config_file: + eprint("No config file was supplied.") + sys.exit(1) + + with open(config_file, "rb") as f: + config = json.load(f) + + if not config: + eprint("Config is empty.") + sys.exit(1) + + eprint("Building composefs dump...") + + paths: dict[str, ComposefsPath] = {} + for attrs in config: + target = attrs["target"] + source = attrs["source"] + mode = attrs["mode"] + + if "*" in source: # Path with globbing + glob_sources = glob.glob(source) + for glob_source in glob_sources: + basename = os.path.basename(glob_source) + glob_target = f"{target}/{basename}" + + composefs_path = ComposefsPath( + attrs, + path=glob_target, + size=100, + filetype=FileType.symlink, + mode="0777", + payload=glob_source, + ) + + paths[glob_target] = composefs_path + add_leading_directories(glob_target, attrs, paths) + else: # Without globbing + if mode == "symlink": + composefs_path = ComposefsPath( + attrs, + # A high approximation of the size of a symlink + size=100, + filetype=FileType.symlink, + mode="0777", + payload=source, + ) + else: + if os.path.isdir(source): + composefs_path = ComposefsPath( + attrs, + size=4096, + filetype=FileType.directory, + mode=mode, + payload=source, + ) + else: + composefs_path = ComposefsPath( + attrs, + size=os.stat(source).st_size, + filetype=FileType.file, + mode=mode, + payload=target, + ) + paths[target] = composefs_path + add_leading_directories(target, attrs, paths) + + composefs_dump = ["/ 4096 40755 1 0 0 0 0.0 - - -"] # Root directory + for key in sorted(paths): + composefs_path = paths[key] + eprint(composefs_path.path) + composefs_dump.append(composefs_path.write_line()) + + print("\n".join(composefs_dump)) + + +if __name__ == "__main__": + main() |