Pin buffer into memory

Make sure the buffer is pinned into memory for I/O.

core/buffer_pool.rs

@@ -19,7 +19,7 @@ impl BufferPool {
         if let Some(buffer) = free_buffers.pop() {
             Buffer::new(self, buffer)
         } else {
-            let raw_buffer = vec![0; self.page_size];
+            let raw_buffer = IoBuffer::allocate(self.page_size);
             Buffer::new(self, raw_buffer)
         }
     }

core/io/darwin.rs

@@ -30,7 +30,7 @@ impl File {
     pub fn pread(&self, pos: usize, buf: &mut Buffer) -> Result<()> {
         let mut file = self.file.borrow_mut();
         file.seek(std::io::SeekFrom::Start(pos as u64))?;
-        file.read_exact(buf)?;
+        file.read_exact(buf.as_mut_slice())?;
         Ok(())
     }
 }

core/io/mod.rs

@@ -1,6 +1,37 @@
 use cfg_block::cfg_block;
+use std::pin::Pin;
 
-pub type Buffer = Vec<u8>;
+pub struct Buffer {
+    data: Pin<Vec<u8>>,
+}
+
+impl Buffer {
+    pub fn allocate(size: usize) -> Self {
+        Self {
+            data: Pin::new(vec![0; size]),
+        }
+    }
+
+    pub fn len(&self) -> usize {
+        self.data.len()
+    }
+
+    pub fn as_slice(&self) -> &[u8] {
+        &self.data
+    }
+
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        &mut self.data
+    }
+
+    pub fn as_ptr(&self) -> *const u8 {
+        self.data.as_ptr()
+    }
+
+    pub fn as_mut_ptr(&mut self) -> *mut u8 {
+        self.data.as_mut_ptr()
+    }
+}
 
 cfg_block! {
     #[cfg(target_os = "linux")] {

core/sqlite3_ondisk.rs

@@ -60,8 +60,9 @@ pub struct DatabaseHeader {
 }
 
 pub fn read_database_header(storage: &Storage) -> Result<DatabaseHeader> {
-    let mut buf = vec![0; 512];
+    let mut buf = crate::Buffer::allocate(512);
     storage.get(1, &mut buf)?;
+    let buf = buf.as_slice();
     let mut header = DatabaseHeader::default();
     header.magic.copy_from_slice(&buf[0..16]);
     header.page_size = u16::from_be_bytes([buf[16], buf[17]]);
@@ -141,6 +142,7 @@ pub fn read_btree_page(
     } else {
         0
     };
+    let page = page.as_slice();
     let mut header = BTreePageHeader {
         page_type: page[pos].try_into()?,
         _first_freeblock_offset: u16::from_be_bytes([page[pos + 1], page[pos + 2]]),