Require kfpath implementation, add to acpi scheme

src/scheme/acpi.rs

@@ -290,6 +290,10 @@ impl KernelScheme for AcpiScheme {
         }
         Ok(buf.finalize())
     }
+    fn kfpath(&self, id: usize, buf: UserSliceWo, token: &mut CleanLockToken) -> Result<usize> {
+        //TODO: construct useful path?
+        buf.copy_common_bytes_from_slice("/scheme/kernel.acpi/".as_bytes())
+    }
     fn kfstat(&self, id: usize, buf: UserSliceWo, token: &mut CleanLockToken) -> Result<()> {
         let handles = HANDLES.read(token.token());
         let handle = handles.get(&id).ok_or(Error::new(EBADF))?;

src/scheme/mod.rs

@@ -481,9 +481,7 @@ pub trait KernelScheme: Send + Sync + 'static {
     ) -> Result<usize> {
         Err(Error::new(EBADF))
     }
-    fn kfpath(&self, id: usize, buf: UserSliceWo, token: &mut CleanLockToken) -> Result<usize> {
-        Err(Error::new(EBADF))
-    }
+    fn kfpath(&self, id: usize, buf: UserSliceWo, token: &mut CleanLockToken) -> Result<usize>;
     fn kfutimens(&self, id: usize, buf: UserSliceRo, token: &mut CleanLockToken) -> Result<usize> {
         Err(Error::new(EBADF))
     }