Add memory scheme, implement fstatvfs

kernel/scheme/memory.rs

@@ -0,0 +1,30 @@
+use arch::memory::{free_frames, used_frames};
+
+use syscall::data::StatVfs;
+use syscall::error::*;
+use syscall::scheme::Scheme;
+
+pub struct MemoryScheme;
+
+impl Scheme for MemoryScheme {
+    fn open(&self, _path: &[u8], _flags: usize, _uid: u32, _gid: u32) -> Result<usize> {
+        Ok(0)
+    }
+
+    fn fstatvfs(&self, _file: usize, stat: &mut StatVfs) -> Result<usize> {
+        let used = used_frames() as u64;
+        let free = free_frames() as u64;
+
+        stat.f_bsize = 4096;
+        stat.f_blocks = used + free;
+        stat.f_bfree = free;
+        stat.f_bavail = stat.f_bfree;
+
+        Ok(0)
+    }
+
+    /// Close the file `number`
+    fn close(&self, _file: usize) -> Result<usize> {
+        Ok(0)
+    }
+}