Add context and file structs

kernel/context/file.rs

@@ -0,0 +1,10 @@
+//! File struct
+
+/// A file
+#[derive(Copy, Clone, Debug)]
+pub struct File {
+    /// The scheme that this file refers to
+    pub scheme: usize,
+    /// The number the scheme uses to refer to this file
+    pub number: usize,
+}

kernel/context/mod.rs

@@ -0,0 +1,34 @@
+//! Context management
+
+/// File operations
+pub mod file;
+
+/// Context list
+pub static mut CONTEXT: Context = Context::new();
+
+/// A context, which identifies either a process or a thread
+#[derive(Copy, Clone, Debug)]
+pub struct Context {
+    /// The open files in the scheme
+    pub files: [Option<file::File>; 32]
+}
+
+impl Context {
+    pub const fn new() -> Context {
+        Context {
+            files: [None; 32]
+        }
+    }
+
+    /// Add a file to the lowest available slot.
+    /// Return the file descriptor number or None if no slot was found
+    pub fn add_file(&mut self, file: file::File) -> Option<usize> {
+        for (i, mut file_option) in self.files.iter_mut().enumerate() {
+            if file_option.is_none() {
+                *file_option = Some(file);
+                return Some(i);
+            }
+        }
+        None
+    }
+}