remove unnecessary features

src/allocator.rs

@@ -11,7 +11,7 @@ const INITIAL_HEAP_SIZE: usize = MEMFD_INITIAL_SIZE;
 const METADATA_SIZE: usize = size_of::<Metadata>();
 
 pub(crate) static ALLOCATOR: LazyLock<Mutex<Allocator>> =
-    LazyLock::new(|| unsafe { Mutex::new(Allocator::new()) });
+    LazyLock::new(|| Mutex::new(Allocator::new()));
 
 struct Metadata {
     chunk: NonNull<Chunk>,
@@ -34,14 +34,14 @@ unsafe impl Send for Chunk {}
 unsafe impl Send for Allocator {}
 
 impl Allocator {
-    unsafe fn new() -> Self {
+    fn new() -> Self {
         let mut allocator = BUMP_ALLOCATOR.lock().unwrap();
 
-        let mem = allocator.alloc(INITIAL_HEAP_SIZE).unwrap();
+        let mem = unsafe { allocator.alloc(INITIAL_HEAP_SIZE).unwrap() };
 
         let head = Box::new(Chunk {
-            buffer: mem.byte_add(METADATA_SIZE),
-            size: INITIAL_HEAP_SIZE,
+            buffer: unsafe { mem.byte_add(METADATA_SIZE) },
+            size: INITIAL_HEAP_SIZE - METADATA_SIZE,
             in_use: false,
             next_chunk: None,
             prev_chunk: None,
@@ -49,27 +49,32 @@ impl Allocator {
         let head = NonNull::new(Box::leak(head)).unwrap();
 
         let mem = mem as *mut Metadata;
+        unsafe {
             *mem = Metadata { chunk: head };
+        }
 
         Allocator { head, tail: head }
     }
 
-    pub(crate) unsafe fn allocate(&mut self, size: usize) -> Option<*mut u8> {
+    pub(crate) fn allocate(&mut self, size: usize) -> Option<*mut u8> {
         let size = (size + ALIGNMENT - 1) / ALIGNMENT * ALIGNMENT;
 
         let mut head = Some(self.head);
 
         while head.is_some() {
-            let current_head = head.unwrap().as_mut();
+            // The heap uses a global Mutex. Only one thread can operate on it at a time.
+            let current_head = unsafe { head.unwrap().as_mut() };
 
             if !current_head.in_use && current_head.size >= size {
-                if current_head.size == size {
+                if current_head.size < (size + METADATA_SIZE + ALIGNMENT) {
                     current_head.in_use = true;
                     return Some(current_head.buffer);
                 }
 
                 let unused_space = Box::new(Chunk {
-                    buffer: current_head.buffer.byte_add(size + METADATA_SIZE),
+                    // We know that size of buffer is larger than size + METADATA_SIZE + ALIGNMENT.
+                    // Therefore size + METADATA_SIZE is still inside of the buffer
+                    buffer: unsafe { current_head.buffer.byte_add(size + METADATA_SIZE) },
                     size: current_head.size - size - METADATA_SIZE,
                     in_use: false,
                     next_chunk: current_head.next_chunk,
@@ -77,12 +82,21 @@ impl Allocator {
                 });
                 let ptr = NonNull::new(Box::leak(unused_space)).unwrap();
 
+                // buffer points to current_head + size + METADATA_SIZE.
+                // Therefore buffer - METADATA_SIZE points right after the buffer of current_head
+                // and right before the buffer of unused_space.
+                // This is where the pointer to the metadata chunk is expected
+                unsafe {
                     *(ptr.as_ref().buffer.byte_sub(METADATA_SIZE) as *mut Metadata) =
                         Metadata { chunk: ptr };
+                }
 
+                // We know that accessing ptr is safe since we just allocated it.
+                unsafe {
                     if ptr.as_ref().next_chunk.is_none() {
                         self.tail = ptr;
                     }
+                }
 
                 current_head.in_use = true;
                 current_head.size = size;
@@ -99,9 +113,9 @@ impl Allocator {
         None
     }
 
-    pub(crate) unsafe fn deallocate(&mut self, ptr: *mut u8) {
-        let metadata = ptr.byte_sub(METADATA_SIZE) as *mut Metadata;
-        let metadata = (*metadata).chunk.as_mut();
+    pub(crate) fn deallocate(&mut self, ptr: *mut u8) {
+        let metadata = unsafe { ptr.byte_sub(METADATA_SIZE) as *mut Metadata };
+        let metadata = unsafe { (*metadata).chunk.as_mut() };
 
         debug_assert_eq!(metadata.in_use, true);
         debug_assert_eq!(metadata.buffer, ptr);
@@ -110,6 +124,11 @@ impl Allocator {
 
         // TODO: Consolidate chunks
     }
+
+    pub(crate) unsafe fn get_offset(&self, ptr: *const u8) -> usize {
+        let allocator = BUMP_ALLOCATOR.lock().unwrap();
+        allocator.get_offset(ptr)
+    }
 }
 
 #[cfg(test)]

src/bump_allocator.rs

@@ -3,10 +3,10 @@ use std::{
     usize,
 };
 
-use libc::{c_char, c_void, ftruncate, memfd_create, mmap, MAP_SHARED, PROT_READ, PROT_WRITE};
+use libc::{c_char, c_void, ftruncate, mmap, perror, syscall, SYS_memfd_secret, MAP_FAILED, MAP_SHARED, PROT_READ, PROT_WRITE};
 
-pub(crate) const MEMFD_INITIAL_SIZE: usize = 1024 * 1024 * 4;
-const MMAP_SIZE: usize = 1024 * 1024 * 1024;
+pub(crate) const MEMFD_INITIAL_SIZE: usize = 1024 * 1024;
+const MMAP_SIZE: usize = 1024 * 1024;
 
 pub(crate) static BUMP_ALLOCATOR: LazyLock<Mutex<BumpAllocator>> =
     LazyLock::new(|| unsafe { Mutex::new(BumpAllocator::new()) });
@@ -26,7 +26,10 @@ impl BumpAllocator {
     unsafe fn new() -> Self {
         assert!(MMAP_SIZE >= MEMFD_INITIAL_SIZE);
 
-        let data_fd = memfd_create("data\x00".as_ptr() as *const c_char, 0);
+        let data_fd = syscall(SYS_memfd_secret, 0) as i32;
+        if data_fd <= 0 {
+            perror("memfd secret\x00".as_ptr() as *const c_char);
+        }
 
         assert!(data_fd > 0);
 
@@ -41,7 +44,7 @@ impl BumpAllocator {
             0,
         ) as *mut u8;
 
-        assert_ne!(start_of_mem, 0 as *mut u8);
+        assert_ne!(start_of_mem, MAP_FAILED as *mut u8);
 
         let end_of_mem = start_of_mem.byte_add(MEMFD_INITIAL_SIZE);
 
@@ -55,7 +58,7 @@ impl BumpAllocator {
         }
     }
 
-    pub unsafe fn alloc(&mut self, size: usize) -> Option<*mut u8> {
+    pub(crate) unsafe fn alloc(&mut self, size: usize) -> Option<*mut u8> {
         let new_head = self.head.byte_add(size);
 
         if new_head > self.end_of_mem {
@@ -75,13 +78,26 @@ impl BumpAllocator {
         ret
     }
 
-    pub fn dealloc(&mut self) {
+    pub(crate) fn dealloc(&mut self) {
         self.number_of_allocated_chunks -= 1;
 
         if self.number_of_allocated_chunks == 0 {
             self.head = self.start_of_mem;
         }
     }
+
+    pub(crate) unsafe fn get_offset(&self, ptr: *const u8) -> usize {
+        let offset = ptr.byte_offset_from(self.start_of_mem);
+
+        debug_assert!(offset >= 0);
+        debug_assert!(offset < self.end_of_mem.byte_offset_from(self.start_of_mem));
+
+        offset as usize
+    }
+
+    pub(crate) fn get_fd(&self) -> i32 {
+        self.backing_fd
+    }
 }
 
 #[cfg(test)]

src/lib.rs

@@ -1,6 +1,11 @@
-#![feature(test)]
-#![feature(lazy_cell)]
+use bump_allocator::BUMP_ALLOCATOR;
 
 mod allocator;
 mod bump_allocator;
 pub mod sharedptr;
+
+pub fn get_shared_mem_fd() -> i32 {
+    let allocator = BUMP_ALLOCATOR.lock().unwrap();
+
+    allocator.get_fd()
+}

src/sharedptr.rs

@@ -1,47 +1,64 @@
 use core::slice;
-use std::{
-    ops::{Deref, DerefMut},
-    usize,
-};
+use std::ops::{Deref, DerefMut};
 
 use crate::allocator::ALLOCATOR;
 
-pub struct SharedPtr<'a>(&'a mut [u8]);
+#[derive(Debug)]
+pub struct SharedPtr {
+    ptr: *mut u8,
+    size: usize
+}
 
-impl SharedPtr<'_> {
+unsafe impl Send for SharedPtr {}
+unsafe impl Sync for SharedPtr {}
+
+impl SharedPtr {
     pub fn new(size: usize) -> Option<Self> {
         let mut allocator = ALLOCATOR.lock().unwrap();
 
-        let buf = unsafe {
         let buf = allocator.allocate(size)?;
-            slice::from_raw_parts_mut(buf, size)
-        };
 
-        Some(SharedPtr(buf))
+        Some(SharedPtr{ptr: buf, size})
+    }
+
+    pub fn get_offset(&self) -> usize {
+        let allocator = ALLOCATOR.lock().unwrap();
+
+        unsafe { allocator.get_offset(self.ptr) }
+    }
+
+    pub fn get_size(&self) -> usize {
+        self.size
     }
 }
 
-impl<'a> Deref for SharedPtr<'a> {
-    type Target = &'a mut [u8];
+impl Deref for SharedPtr {
+    type Target = [u8];
 
     fn deref(&self) -> &Self::Target {
-        &self.0
+        unsafe {
+            slice::from_raw_parts(self.ptr, self.size)
+                .try_into()
+                .expect("This should never fail")
+        }
     }
 }
 
-impl<'a> DerefMut for SharedPtr<'a> {
+impl DerefMut for SharedPtr {
     fn deref_mut(&mut self) -> &mut Self::Target {
-        &mut self.0
+        unsafe {
+            slice::from_raw_parts_mut(self.ptr, self.size)
+                .try_into()
+                .expect("This should never fail")
+        }
     }
 }
 
-impl Drop for SharedPtr<'_> {
+impl Drop for SharedPtr {
     fn drop(&mut self) {
         let mut allocator = ALLOCATOR.lock().unwrap();
 
-        unsafe {
-            allocator.deallocate(self.0.as_mut_ptr());
-        }
+        allocator.deallocate(self.ptr);
     }
 }
 
@@ -56,4 +73,12 @@ mod tests {
         assert_eq!(x[0], 1);
         drop(x);
     }
+
+    #[test]
+    fn slice() {
+        let mut x = SharedPtr::new(10).unwrap();
+        x[0] = 1;
+        x[1] = 2;
+        assert_eq!(x[0..=1], [1, 2]);
+    }
 }