refactor: move umount to the common executable

src/main.rs

@@ -10,6 +10,7 @@ mod mount;
 mod nologin;
 mod ps;
 mod rmmod;
+mod umount;
 
 use std::env;
 use utils::error;
@@ -34,7 +35,7 @@ fn main() {
             todo!()
         }
         "mount" => mount::main(args),
-        "umount" => todo!(),
+        "umount" => umount::main(args),
         "nologin" => nologin::main(),
         "powerctl" => todo!(),
         "halt" => todo!(),

src/umount.rs

@@ -0,0 +1,68 @@
+//! The `mount` command allows to unmount a filesystem.
+
+use std::env::ArgsOs;
+use std::ffi::{CStr, CString};
+use std::fs;
+use std::io;
+use std::io::Error;
+use std::os::unix::ffi::OsStrExt;
+use std::path::PathBuf;
+use std::process::exit;
+use utils::error;
+
+/// Prints the command's usage.
+///
+/// `bin` is the name of the current binary.
+fn print_usage() {
+    eprintln!("Usage:");
+    eprintln!(" umount [-R] dir");
+    eprintln!();
+    eprintln!("Options:");
+    eprintln!(" -R:\tunmounts filesystems recursively");
+    eprintln!(" dir:\tthe mountpoint path");
+}
+
+/// Unmounts the filesystem at the given path `target`.
+pub fn unmount_fs(target: &CStr) -> io::Result<()> {
+    let ret = unsafe { libc::umount(target.as_ptr() as _) };
+    if ret < 0 {
+        return Err(Error::last_os_error());
+    }
+    Ok(())
+}
+
+pub fn main(args: ArgsOs) {
+    let args: Vec<_> = args.collect();
+    match &args[..] {
+        [opt, path] if opt == "-R" => {
+            // List active mount points
+            let content = fs::read_to_string("/etc/mtab").unwrap_or_else(|e| {
+                error("umount", format_args!("cannot list mount points: {e}"))
+            });
+            let mut mps: Vec<_> = content
+                .split('\n')
+                .filter_map(|entry| Some(entry.split(' ').nth(1)?.into()))
+                // Filter matching paths
+                .filter(|mp: &PathBuf| mp.starts_with(path))
+                .collect();
+            // Sort to unmount in the right order
+            mps.sort_unstable();
+            for mp in mps.into_iter().rev() {
+                let s = CString::new(mp.as_os_str().as_bytes()).unwrap();
+                unmount_fs(&s).unwrap_or_else(|e| {
+                    error("umount", format_args!("cannot unmount `{}`: {e}", path.display()));
+                });
+            }
+        }
+        [path] => {
+            let s = CString::new(args[1].as_bytes()).unwrap();
+            unmount_fs(&s).unwrap_or_else(|e| {
+                error("umount", format_args!("cannot unmount `{}`: {e}", path.display()));
+            });
+        }
+        _ => {
+            print_usage();
+            exit(1);
+        }
+    }
+}