[Closes #371] Use const Default trait in arena.

kernel-rs/Cargo.toml

@@ -26,7 +26,7 @@ scopeguard = { version = "1.1.0", default-features = false }
 arrayvec = { version = "0.5.2", default-features = false }
 cstr_core = { version = "0.2.2", default-features = false }
 spin = { version = "0.7.1", default-features = false }
-array-macro = "2.0.0"
+array-macro = "2.1.0"
 static_assertions = "1.1.0"
 itertools = { version = "0.10.0", default-features = false }
 pin-project = "1"

kernel-rs/src/arena.rs

@@ -3,6 +3,7 @@ use core::mem::{self, ManuallyDrop};
 use core::ops::Deref;
 use core::pin::Pin;
 
+use array_macro::array;
 use pin_project::pin_project;
 
 use crate::list::*;
@@ -124,9 +125,21 @@ pub struct Rc<A: Arena> {
 unsafe impl<T: Sync, A: Arena<Data = T>> Send for Rc<A> {}
 
 impl<T, const CAPACITY: usize> ArrayArena<T, CAPACITY> {
-    // TODO(https://github.com/kaist-cp/rv6/issues/371): unsafe...
-    pub const fn new(entries: [RcCell<T>; CAPACITY]) -> Self {
-        Self { entries }
+    /// Returns an `ArrayArena` of size `CAPACITY` that is filled with `D`'s const default value.
+    /// Note that `D` must `impl const Default`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// let arr_arena = ArrayArena::<D, 100>::new();
+    /// ```
+    // Note: We cannot use the generic `T` in the following function, since we need to only allow
+    // types that `impl const Default`, not just `impl Default`.
+    #[allow(clippy::new_ret_no_self)]
+    pub const fn new<D: Default>() -> ArrayArena<D, CAPACITY> {
+        ArrayArena {
+            entries: array![_ => RcCell::new(Default::default()); CAPACITY],
+        }
     }
 }
 
@@ -246,10 +259,20 @@ unsafe impl<T> ListNode for MruEntry<T> {
 }
 
 impl<T, const CAPACITY: usize> MruArena<T, CAPACITY> {
-    // TODO(https://github.com/kaist-cp/rv6/issues/371): unsafe...
-    pub const fn new(entries: [MruEntry<T>; CAPACITY]) -> Self {
-        Self {
-            entries,
+    /// Returns an `MruArena` of size `CAPACITY` that is filled with `D`'s const default value.
+    /// Note that `D` must `impl const Default`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// let mru_arena = MruArena::<D, 100>::new();
+    /// ```
+    // Note: We cannot use the generic `T` in the following function, since we need to only allow
+    // types that `impl const Default`, not just `impl Default`.
+    #[allow(clippy::new_ret_no_self)]
+    pub const fn new<D: Default>() -> MruArena<D, CAPACITY> {
+        MruArena {
+            entries: array![_ => MruEntry::new(Default::default()); CAPACITY],
             list: unsafe { List::new() },
         }
     }

kernel-rs/src/bio.rs

@@ -14,10 +14,8 @@
 use core::mem::{self, ManuallyDrop};
 use core::ops::{Deref, DerefMut};
 
-use array_macro::array;
-
 use crate::{
-    arena::{Arena, ArenaObject, MruArena, MruEntry, Rc},
+    arena::{Arena, ArenaObject, MruArena, Rc},
     lock::{Sleeplock, Spinlock},
     param::{BSIZE, NBUF},
     proc::WaitChannel,
@@ -44,6 +42,13 @@ impl BufEntry {
     }
 }
 
+#[rustfmt::skip] // Need this if lower than rustfmt 1.4.34
+impl const Default for BufEntry {
+    fn default() -> Self {
+        Self::zero()
+    }
+}
+
 impl ArenaObject for BufEntry {
     fn finalize<'s, A: Arena>(&'s mut self, _guard: &'s mut A::Guard<'_>) {
         // The buffer contents should have been written. Does nothing.
@@ -149,12 +154,7 @@ impl Bcache {
     ///
     /// The caller should make sure that `Bcache` never gets moved.
     pub const unsafe fn zero() -> Self {
-        unsafe {
-            Spinlock::new(
-                "BCACHE",
-                MruArena::new(array![_ => MruEntry::new(BufEntry::zero()); NBUF]),
-            )
-        }
+        Spinlock::new("BCACHE", MruArena::<BufEntry, NBUF>::new())
     }
 
     /// Return a unlocked buf with the contents of the indicated block.

kernel-rs/src/file.rs

@@ -2,8 +2,6 @@
 
 use core::{cell::UnsafeCell, cmp, mem, ops::Deref, ops::DerefMut};
 
-use array_macro::array;
-
 use crate::{
     arena::{Arena, ArenaObject, ArrayArena, Rc},
     fs::{FileSystem, InodeGuard, RcInode},
@@ -12,7 +10,6 @@ use crate::{
     param::{BSIZE, MAXOPBLOCKS, NFILE},
     pipe::AllocatedPipe,
     proc::CurrentProc,
-    rc_cell::RcCell,
     vm::UVAddr,
 };
 
@@ -201,6 +198,13 @@ impl File {
     }
 }
 
+#[rustfmt::skip] // Need this if lower than rustfmt 1.4.34
+impl const Default for File {
+    fn default() -> Self {
+        Self::zero()
+    }
+}
+
 impl ArenaObject for File {
     fn finalize<'s, A: Arena>(&'s mut self, guard: &'s mut A::Guard<'_>) {
         // SAFETY: `FileTable` does not use `Arena::find_or_alloc`.
@@ -235,10 +239,7 @@ impl ArenaObject for File {
 
 impl FileTable {
     pub const fn zero() -> Self {
-        Spinlock::new(
-            "FTABLE",
-            ArrayArena::new(array![_ => RcCell::new(File::zero()); NFILE]),
-        )
+        Spinlock::new("FTABLE", ArrayArena::<File, NFILE>::new())
     }
 
     /// Allocate a file structure.

kernel-rs/src/fs/inode.rs

@@ -74,7 +74,6 @@ use core::{
     ptr,
 };
 
-use array_macro::array;
 use static_assertions::const_assert;
 
 use super::{FileName, IPB, MAXFILE, NDIRECT, NINDIRECT};
@@ -87,7 +86,6 @@ use crate::{
     param::ROOTDEV,
     param::{BSIZE, NINODE},
     proc::CurrentProc,
-    rc_cell::RcCell,
     stat::Stat,
     vm::UVAddr,
 };
@@ -675,6 +673,13 @@ impl InodeGuard<'_> {
     }
 }
 
+#[rustfmt::skip] // Need this if lower than rustfmt 1.4.34
+impl const Default for Inode {
+    fn default() -> Self {
+        Self::zero()
+    }
+}
+
 impl ArenaObject for Inode {
     /// Drop a reference to an in-memory inode.
     /// If that was the last reference, the inode table entry can
@@ -810,10 +815,7 @@ impl Inode {
 
 impl Itable {
     pub const fn zero() -> Self {
-        Spinlock::new(
-            "ITABLE",
-            ArrayArena::new(array![_ => RcCell::new(Inode::zero()); NINODE]),
-        )
+        Spinlock::new("ITABLE", ArrayArena::<Inode, NINODE>::new())
     }
 
     /// Find the inode with number inum on device dev

kernel-rs/src/lib.rs

@@ -49,6 +49,8 @@
 #![feature(array_value_iter)]
 #![feature(const_fn)]
 #![feature(const_fn_union)]
+#![feature(const_trait_impl)]
+#![feature(const_precise_live_drops)]
 #![feature(maybe_uninit_extra)]
 #![feature(generic_associated_types)]
 #![feature(unsafe_block_in_unsafe_fn)]