config: remount rw/ro during configuration saving process

Until there's decent OverlayFS support for configuration, just remount.
Without it, the whole configuration web server is basically useless.

Author: manio

src/config.rs

@@ -2,12 +2,18 @@ use bluer::Address;
 use serde::de::{self, Deserializer, Error as DeError, Visitor};
 use serde::{Deserialize, Serialize};
 use simplelog::*;
-use std::fmt::{self, Display};
-use std::fs;
-use std::path::PathBuf;
-use std::str::FromStr;
+use std::{
+    fmt::{self, Display},
+    fs, io,
+    path::PathBuf,
+    process::{Command, Stdio},
+    str::FromStr,
+};
 use toml_edit::{value, DocumentMut};
 
+// module name for logging engine
+const NAME: &str = "<i><bright-black> config: </>";
+
 #[derive(
     clap::ValueEnum, Default, Debug, PartialEq, PartialOrd, Clone, Copy, Deserialize, Serialize,
 )]
@@ -170,6 +176,34 @@ impl Default for AppConfig {
     }
 }
 
+/// Remount `/` as readonly (`lock = true`) or read-write (`lock = false`)
+fn remount_root(lock: bool) -> io::Result<()> {
+    let mode = if lock { "remount,ro" } else { "remount,rw" };
+
+    let status = Command::new("mount")
+        .args(&["-o", mode, "/"])
+        .stdout(Stdio::null())
+        .stderr(Stdio::null())
+        .status()?;
+
+    if status.success() {
+        info!(
+            "{} Remount as {} successful",
+            NAME,
+            if lock { "read-only" } else { "read-write" }
+        );
+    } else {
+        error!(
+            "{} Remount as {} failed: {:?}",
+            NAME,
+            if lock { "read-only" } else { "read-write" },
+            status
+        );
+    }
+
+    Ok(())
+}
+
 impl AppConfig {
     pub fn load(config_file: PathBuf) -> Result<Self, Box<dyn std::error::Error>> {
         use ::config::File;
@@ -235,6 +269,13 @@ impl AppConfig {
         doc["ev_battery_capacity"] = value(self.ev_battery_capacity as i64);
         doc["ev_factor"] = value(self.ev_factor as f64);
 
+        let _ = remount_root(false);
+        info!(
+            "{} Saving new configuration to file: {}",
+            NAME,
+            config_file.display()
+        );
         let _ = fs::write(config_file, doc.to_string());
+        let _ = remount_root(true);
     }
 }