feat: add error message to creating memfd

src/allocator.rs

@@ -110,6 +110,11 @@ 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 +1,14 @@
 #![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

@@ -1,46 +1,58 @@
 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<const N: usize>(*mut u8);
 
-impl SharedPtr<'_> {
-    pub fn new(size: usize) -> Option<Self> {
+unsafe impl<const N: usize> Send for SharedPtr<N> {}
+unsafe impl<const N: usize> Sync for SharedPtr<N> {}
+
+impl<const N: usize> SharedPtr<N> {
+    pub fn new() -> Option<Self> {
         let mut allocator = ALLOCATOR.lock().unwrap();
 
-        let buf = unsafe {
-            let buf = allocator.allocate(size)?;
-            slice::from_raw_parts_mut(buf, size)
-        };
+        let buf = unsafe { allocator.allocate(N)? };
 
         Some(SharedPtr(buf))
     }
+
+    pub fn get_offset(&self) -> usize {
+        let allocator = ALLOCATOR.lock().unwrap();
+
+        unsafe { allocator.get_offset(self.as_ptr()) }
+    }
 }
 
-impl<'a> Deref for SharedPtr<'a> {
-    type Target = &'a mut [u8];
+impl<const N: usize> Deref for SharedPtr<N> {
+    type Target = [u8; N];
 
     fn deref(&self) -> &Self::Target {
-        &self.0
+        unsafe {
+            slice::from_raw_parts(self.0, N)
+                .try_into()
+                .expect("This should never fail")
+        }
     }
 }
 
-impl<'a> DerefMut for SharedPtr<'a> {
+impl<const N: usize> DerefMut for SharedPtr<N> {
     fn deref_mut(&mut self) -> &mut Self::Target {
-        &mut self.0
+        unsafe {
+            slice::from_raw_parts_mut(self.0, N)
+                .try_into()
+                .expect("This should never fail")
+        }
     }
 }
 
-impl Drop for SharedPtr<'_> {
+impl<const N: usize> Drop for SharedPtr<N> {
     fn drop(&mut self) {
         let mut allocator = ALLOCATOR.lock().unwrap();
 
         unsafe {
-            allocator.deallocate(self.0.as_mut_ptr());
+            allocator.deallocate(self.0);
         }
     }
 }
@@ -51,9 +63,17 @@ mod tests {
 
     #[test]
     fn test() {
-        let mut x = SharedPtr::new(10).unwrap();
+        let mut x = SharedPtr::<10>::new().unwrap();
         x[0] = 1;
         assert_eq!(x[0], 1);
         drop(x);
     }
+
+    #[test]
+    fn slice() {
+        let mut x = SharedPtr::<10>::new().unwrap();
+        x[0] = 1;
+        x[1] = 2;
+        assert_eq!(x[0..=1], [1, 2]);
+    }
 }