ksud: refine su and make it compitable with MagiskSU

Supported features:

1.  --mount-master, -M, -mm which would make the command run in global mount namespace.
2. - user to switch a specific user's shell.
3. -v, -V to print version code and name.

fix #330 #306 #305 #32

userspace/ksud/src/utils.rs

@@ -1,7 +1,7 @@
 use anyhow::{bail, Context, Error, Ok, Result};
 use std::{
-    fs::{create_dir_all, write, File},
-    io::ErrorKind::AlreadyExists,
+    fs::{create_dir_all, write, File, OpenOptions},
+    io::{ErrorKind::AlreadyExists, Write},
     path::Path,
 };
 
@@ -116,6 +116,32 @@ pub fn unshare_mnt_ns() -> Result<()> {
     Ok(())
 }
 
+fn switch_cgroup(grp: &str, pid: u32) {
+    let path = Path::new(grp).join("cgroup.procs");
+    if !path.exists() {
+        return;
+    }
+
+    let fp = OpenOptions::new().append(true).open(path);
+    if let std::result::Result::Ok(mut fp) = fp {
+        let _ = writeln!(fp, "{pid}");
+    }
+}
+
+pub fn switch_cgroups() {
+    let pid = std::process::id();
+    switch_cgroup("/acct", pid);
+    switch_cgroup("/dev/cg2_bpf", pid);
+    switch_cgroup("/sys/fs/cgroup", pid);
+
+    if getprop("ro.config.per_app_memcg")
+        .filter(|prop| prop == "false")
+        .is_none()
+    {
+        switch_cgroup("/dev/memcg/apps", pid);
+    }
+}
+
 #[cfg(any(target_os = "linux", target_os = "android"))]
 pub fn umask(mask: u32) {
     unsafe { libc::umask(mask) };