chore: Reinstate linux_kernel_command_line package (#8240)

This package was removed in #7739
because there were no users, but it's actually a useful package that can
be used to read kernel line arguments from Rust. Later PRs will use it.

I did some optimization/simplification on the original code.

Author: frankdavid

Cargo.lock

@@ -180,6 +180,7 @@ members = [
     "rs/ic_os/guest_upgrade/server",
     "rs/ic_os/guest_upgrade/shared",
     "rs/ic_os/guest_upgrade/tests",
+    "rs/ic_os/linux_kernel_command_line",
     "rs/ic_os/metrics_tool",
     "rs/ic_os/network",
     "rs/ic_os/nft_exporter",

Cargo.toml

@@ -5,6 +5,7 @@ package(default_visibility = ["//rs:ic-os-pkg"])
 DEPENDENCIES = [
     # Keep sorted.
     "//rs/ic_os/build_tools/partition_tools",
+    "//rs/ic_os/linux_kernel_command_line",
     "@crate_index//:anyhow",
     "@crate_index//:clap",
     "@crate_index//:regex",

rs/ic_os/dev_test_tools/setupos-disable-checks/BUILD.bazel

@@ -7,6 +7,7 @@ edition.workspace = true
 anyhow = { workspace = true }
 clap = { workspace = true }
 indoc = { workspace = true }
+linux_kernel_command_line = { path = "../../linux_kernel_command_line" }
 partition_tools = { path = "../../build_tools/partition_tools" }
 regex = { workspace = true }
 tempfile = { workspace = true }

rs/ic_os/dev_test_tools/setupos-disable-checks/Cargo.toml

@@ -1,10 +1,12 @@
-use anyhow::{Context, Error};
+use anyhow::{Context, Result};
 use clap::Parser;
+use linux_kernel_command_line::KernelCommandLine;
 use regex::Regex;
 use std::fs;
 use std::fs::Permissions;
 use std::os::unix::fs::PermissionsExt;
 use std::path::{Path, PathBuf};
+use std::str::FromStr;
 use tempfile::NamedTempFile;
 
 use partition_tools::{Partition, ext::ExtPartition};
@@ -22,7 +24,7 @@ struct Cli {
     compat: bool,
 }
 
-fn main() -> Result<(), Error> {
+fn main() -> Result<()> {
     let cli = Cli::parse();
     let boot_args_path = Path::new("/boot_args");
 
@@ -39,7 +41,7 @@ fn main() -> Result<(), Error> {
         process_cmdline(
             std::str::from_utf8(&bootfs.read_file(boot_args_path)?)?,
             cli.compat,
-        ),
+        )?,
     )
     .context("failed to write temporary boot args")?;
     fs::set_permissions(temp_boot_args.path(), Permissions::from_mode(0o755))?;
@@ -55,7 +57,7 @@ fn main() -> Result<(), Error> {
 }
 
 /// Disable checks from the kernel command line
-fn process_cmdline(input: &str, compat: bool) -> String {
+fn process_cmdline(input: &str, compat: bool) -> Result<String> {
     let boot_args_re = Regex::new(r"(^|\n)BOOT_ARGS=(.*)(\s+#|\n|$)").unwrap();
 
     let left;
@@ -82,33 +84,30 @@ fn process_cmdline(input: &str, compat: bool) -> String {
         }
     };
 
-    let requires_space = !boot_args.is_empty();
-    let mut boot_args = format!(
-        "{boot_args}{sep}ic.setupos.run_checks=0",
-        sep = if requires_space { " " } else { "" }
-    );
+    let mut cmdline = KernelCommandLine::from_str(boot_args)?;
+    cmdline.ensure_single_argument("ic.setupos.run_checks", Some("0"))?;
 
     // TODO: Remove with NODE-1791
     // Disable old flags for temporary backwards compatibility
     if compat {
-        boot_args = format!(
-            "{boot_args} ic.setupos.check_hardware=0 ic.setupos.check_network=0 ic.setupos.check_age=0",
-        );
+        cmdline.ensure_single_argument("ic.setupos.check_hardware", Some("0"))?;
+        cmdline.ensure_single_argument("ic.setupos.check_network", Some("0"))?;
+        cmdline.ensure_single_argument("ic.setupos.check_age", Some("0"))?;
     }
 
-    format!(
-        "# This file has been modified by setupos-disable-checks.\n{file_start}{indent}BOOT_ARGS=\"{boot_args}\"{tail}{file_end}",
+    Ok(format!(
+        "# This file has been modified by setupos-disable-checks.\n{file_start}{indent}BOOT_ARGS=\"{cmdline}\"{tail}{file_end}",
         file_start = &input[..left],
         file_end = &input[right..],
-    )
+    ))
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
     fn test(input: &str, expected: &str) {
-        let result = process_cmdline(input, false);
+        let result = process_cmdline(input, false).unwrap();
 
         assert_eq!(
             expected,

rs/ic_os/dev_test_tools/setupos-disable-checks/src/main.rs

@@ -0,0 +1,17 @@
+load("@rules_rust//rust:defs.bzl", "rust_library", "rust_test")
+
+package(default_visibility = ["//visibility:public"])
+
+rust_library(
+    name = "linux_kernel_command_line",
+    srcs = glob(["src/**"]),
+    deps = [
+        # Keep sorted.
+        "@crate_index//:regex",
+    ],
+)
+
+rust_test(
+    name = "unit_tests",
+    crate = ":linux_kernel_command_line",
+)

rs/ic_os/linux_kernel_command_line/BUILD.bazel

@@ -0,0 +1,11 @@
+[package]
+name = "linux_kernel_command_line"
+description = "Utilities to manipulate a kernel command line reliably."
+license = "Apache-2.0"
+version.workspace = true
+authors.workspace = true
+edition.workspace = true
+documentation.workspace = true
+
+[dependencies]
+regex = { workspace = true }