Fix temp dir on Android 10 or below (#1250)

Co-authored-by: Ylarod <me@ylarod.cn>

userspace/ksud/src/cli.rs

@@ -48,6 +48,9 @@ enum Commands {
         command: Profile,
     },
 
+    /// Print KernelSU tmpfs path
+    Path,
+
     /// For developers
     Debug {
         #[command(subcommand)]
@@ -228,6 +231,10 @@ pub fn run() -> Result<()> {
             Profile::DeleteTemplate { id } => crate::profile::delete_template(id),
             Profile::ListTemplates => crate::profile::list_templates(),
         },
+        Commands::Path => {
+            println!("{}", utils::get_tmp_path());
+            Ok(())
+        }
 
         Commands::Debug { command } => match command {
             Debug::SetManager { apk } => debug::set_manager(&apk),

userspace/ksud/src/defs.rs

@@ -25,7 +25,8 @@ pub const MODULE_UPDATE_TMP_IMG: &str = concatcp!(WORKING_DIR, "update_tmp.img")
 // warning: this directory should not change, or you need to change the code in module_installer.sh!!!
 pub const MODULE_UPDATE_TMP_DIR: &str = concatcp!(ADB_DIR, "modules_update/");
 
-pub const TEMP_DIR: &str = "/debug_ramdisk/";
+pub const TEMP_DIR: &str = "/debug_ramdisk";
+pub const TEMP_DIR_LEGACY: &str = "/sbin";
 
 pub const DISABLE_FILE_NAME: &str = "disable";
 pub const UPDATE_FILE_NAME: &str = "update";

userspace/ksud/src/event.rs

@@ -179,7 +179,7 @@ pub fn on_post_data_fs() -> Result<()> {
     }
 
     // mount temp dir
-    if let Err(e) = mount::mount_tmpfs(defs::TEMP_DIR) {
+    if let Err(e) = mount::mount_tmpfs(utils::get_tmp_path()) {
         warn!("do temp dir mount failed: {}", e);
     }
 

userspace/ksud/src/utils.rs

@@ -5,6 +5,8 @@ use std::{
     path::Path,
 };
 
+use crate::defs;
+use std::fs::metadata;
 #[allow(unused_imports)]
 use std::fs::{set_permissions, Permissions};
 #[cfg(unix)]
@@ -163,3 +165,13 @@ pub fn umask(_mask: u32) {
 pub fn has_magisk() -> bool {
     which::which("magisk").is_ok()
 }
+
+pub fn get_tmp_path() -> &'static str {
+    if metadata(defs::TEMP_DIR_LEGACY).is_ok() {
+        return defs::TEMP_DIR_LEGACY;
+    }
+    if metadata(defs::TEMP_DIR).is_ok() {
+        return defs::TEMP_DIR;
+    }
+    ""
+}