Allow specifying default configuration through a configuration file

Muvm will first look in $XDG_CONFIG_DIR:-~/.config for a muvm/config.json
file. Failing this, it will try reading /etc/muvm/config.json.

Currently the configuration file only allows *prepending* execute_pre
option. Specifying --execute-pre will not overwrite what's already
in the config file.

Signed-off-by: Nikodem Rabuliński <[email protected]>

Author: nrabulinski

crates/muvm/src/bin/muvm.rs

@@ -15,6 +15,7 @@ use krun_sys::{
 };
 use log::debug;
 use muvm::cli_options::options;
+use muvm::config::Configuration;
 use muvm::cpu::{get_fallback_cores, get_performance_cores};
 use muvm::env::{find_muvm_exec, prepare_env_vars};
 use muvm::hidpipe_server::spawn_hidpipe_server;
@@ -73,6 +74,12 @@ fn main() -> Result<ExitCode> {
     }
 
     let options = options().fallback_to_usage().run();
+    let config = Configuration::parse_config_file()?;
+
+    let mut init_commands = options.init_commands;
+    if let Some(init_command) = config.execute_pre {
+        init_commands.insert(0, init_command);
+    }
 
     let (_lock_file, command, command_args, env) = match launch_or_lock(
         options.command,
@@ -397,7 +404,7 @@ fn main() -> Result<ExitCode> {
         merged_rootfs: options.merged_rootfs,
         emulator: options.emulator,
         cwd,
-        init_commands: options.init_commands,
+        init_commands,
     };
     let mut muvm_config_file = NamedTempFile::new()
         .context("Failed to create a temporary file to store the muvm guest config")?;

crates/muvm/src/config.rs

@@ -0,0 +1,59 @@
+use std::{
+    env::{self, VarError},
+    io,
+    path::{Path, PathBuf},
+};
+
+use anyhow::{Context, Result};
+use serde::{Deserialize, Serialize};
+
+#[derive(Deserialize, Serialize, Default)]
+pub struct Configuration {
+    pub execute_pre: Option<PathBuf>,
+}
+
+fn get_var_if_exists(name: &str) -> Option<Result<String>> {
+    match env::var(name) {
+        Ok(val) => Some(Ok(val)),
+        Err(VarError::NotPresent) => None,
+        Err(e) => Some(Err(e.into())),
+    }
+}
+
+fn get_user_config_path() -> Result<PathBuf> {
+    let mut path = get_var_if_exists("XDG_CONFIG_DIR").map_or_else(
+        || {
+            let base = env::var("HOME").context("Failed to get HOME")?;
+            let mut base = PathBuf::from(base);
+            base.push(".config");
+            Ok(base)
+        },
+        |p| p.map(PathBuf::from),
+    )?;
+    path.push("muvm");
+    path.push("config.json");
+    Ok(path)
+}
+
+fn get_system_config_path() -> PathBuf {
+    PathBuf::from("/etc/muvm/config.json")
+}
+
+fn read_to_string_if_exists(p: &Path) -> Option<io::Result<String>> {
+    match std::fs::read_to_string(p) {
+        Ok(content) => Some(Ok(content)),
+        Err(err) if err.kind() == io::ErrorKind::NotFound => None,
+        Err(e) => Some(Err(e)),
+    }
+}
+
+impl Configuration {
+    pub fn parse_config_file() -> Result<Self> {
+        let Some(content) = read_to_string_if_exists(&get_user_config_path()?)
+            .or_else(|| read_to_string_if_exists(&get_system_config_path()))
+        else {
+            return Ok(Default::default());
+        };
+        Ok(serde_json::from_str(&content?)?)
+    }
+}

crates/muvm/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod cli_options;
+pub mod config;
 pub mod cpu;
 pub mod env;
 pub mod hidpipe_common;