diff --git a/bindings/wasm/lib.rs b/bindings/wasm/lib.rs
index 28970b057..c7007a9a2 100644
--- a/bindings/wasm/lib.rs
+++ b/bindings/wasm/lib.rs
@@ -19,7 +19,7 @@ impl Database {
 pub struct IO {}
 
 impl limbo_core::StorageIO for IO {
-    fn get(&self, _page_idx: usize, _buf: &mut limbo_core::Buffer) -> Result<()> {
+    fn get(&self, _page_idx: usize, _c: &mut limbo_core::Completion) -> Result<()> {
         todo!();
     }
 }
diff --git a/core/io/darwin.rs b/core/io/darwin.rs
index 64ecc1369..eac13e84d 100644
--- a/core/io/darwin.rs
+++ b/core/io/darwin.rs
@@ -1,4 +1,4 @@
-use super::Buffer;
+use super::Completion;
 use anyhow::{Ok, Result};
 use std::cell::RefCell;
 use std::io::{Read, Seek};
@@ -27,10 +27,10 @@ pub struct File {
 }
 
 impl File {
-    pub fn pread(&self, pos: usize, buf: &mut Buffer) -> Result<()> {
+    pub fn pread(&self, pos: usize, c: &mut Completion) -> Result<()> {
         let mut file = self.file.borrow_mut();
         file.seek(std::io::SeekFrom::Start(pos as u64))?;
-        file.read_exact(buf.as_mut_slice())?;
+        file.read_exact(c.buf.as_mut_slice())?;
         Ok(())
     }
 }
\ No newline at end of file
diff --git a/core/io/linux.rs b/core/io/linux.rs
index 91677be8c..55e1c8af0 100644
--- a/core/io/linux.rs
+++ b/core/io/linux.rs
@@ -1,4 +1,4 @@
-use super::Buffer;
+use super::Completion;
 use anyhow::Result;
 use std::cell::RefCell;
 use std::os::unix::io::AsRawFd;
@@ -38,9 +38,9 @@ pub struct File {
 }
 
 impl File {
-    pub fn pread(&self, pos: usize, buf: &mut Buffer) -> Result<()> {
+    pub fn pread(&self, pos: usize, c: &mut Completion) -> Result<()> {
         let fd = io_uring::types::Fd(self.file.as_raw_fd());
-        let read_e = io_uring::opcode::Read::new(fd, buf.as_mut_ptr(), buf.len() as u32 )
+        let read_e = io_uring::opcode::Read::new(fd, c.buf.as_mut_ptr(), buf.len() as u32 )
             .offset(pos as u64)
             .build();
         let mut ring = self.ring.borrow_mut();
diff --git a/core/io/mod.rs b/core/io/mod.rs
index aaa0ea65b..78f988049 100644
--- a/core/io/mod.rs
+++ b/core/io/mod.rs
@@ -1,6 +1,10 @@
 use cfg_block::cfg_block;
 use std::pin::Pin;
 
+pub struct Completion<'a> {
+    pub buf: &'a mut Buffer,
+}
+
 pub struct Buffer {
     data: Pin<Vec<u8>>,
 }
diff --git a/core/lib.rs b/core/lib.rs
index cbd8ea37c..0e9b8f6e0 100644
--- a/core/lib.rs
+++ b/core/lib.rs
@@ -20,9 +20,9 @@ use schema::Schema;
 use sqlite3_parser::{ast::Cmd, lexer::sql::Parser};
 use std::sync::Arc;
 
-pub use io::{Buffer};
 #[cfg(feature = "fs")]
 pub use io::IO;
+pub use io::{Buffer, Completion};
 pub use storage::{Storage, StorageIO};
 pub use types::Value;
 
diff --git a/core/sqlite3_ondisk.rs b/core/sqlite3_ondisk.rs
index 0e933aa76..e62b1a501 100644
--- a/core/sqlite3_ondisk.rs
+++ b/core/sqlite3_ondisk.rs
@@ -24,6 +24,7 @@
 ///
 /// For more information, see: https://www.sqlite.org/fileformat.html
 use crate::buffer_pool::BufferPool;
+use crate::io::{Buffer, Completion};
 use crate::types::{Record, Value};
 use crate::Storage;
 use anyhow::{anyhow, Result};
@@ -60,8 +61,11 @@ pub struct DatabaseHeader {
 }
 
 pub fn read_database_header(storage: &Storage) -> Result<DatabaseHeader> {
-    let mut buf = crate::Buffer::allocate(512);
-    storage.get(1, &mut buf)?;
+    let mut buf = Buffer::allocate(512);
+    let mut c = Completion {
+        buf: buf.borrow_mut(),
+    };
+    storage.get(1, &mut c)?;
     let buf = buf.as_slice();
     let mut header = DatabaseHeader::default();
     header.magic.copy_from_slice(&buf[0..16]);
@@ -136,7 +140,8 @@ pub fn read_btree_page(
 ) -> Result<BTreePage> {
     let mut buf = buffer_pool.get();
     let page = buf.borrow_mut().data_mut();
-    storage.get(page_idx, page)?;
+    let mut c = Completion { buf: page };
+    storage.get(page_idx, &mut c)?;
     let mut pos = if page_idx == 1 {
         DATABASE_HEADER_SIZE
     } else {
diff --git a/core/storage.rs b/core/storage.rs
index 635391f7b..7f49e2201 100644
--- a/core/storage.rs
+++ b/core/storage.rs
@@ -1,4 +1,4 @@
-use crate::io::{Buffer};
+use crate::io::Completion;
 use anyhow::Result;
 use std::sync::Arc;
 
@@ -18,13 +18,13 @@ impl Storage {
         }
     }
 
-    pub fn get(&self, page_idx: usize, buf: &mut Buffer) -> Result<()> {
-        self.io.get(page_idx, buf)
+    pub fn get(&self, page_idx: usize, c: &mut Completion) -> Result<()> {
+        self.io.get(page_idx, c)
     }
 }
 
 pub trait StorageIO {
-    fn get(&self, page_idx: usize, buf: &mut Buffer) -> Result<()>;
+    fn get(&self, page_idx: usize, c: &mut Completion) -> Result<()>;
 }
 
 #[cfg(feature = "fs")]
@@ -34,14 +34,14 @@ struct FileStorage {
 
 #[cfg(feature = "fs")]
 impl StorageIO for FileStorage {
-    fn get(&self, page_idx: usize, buf: &mut Buffer) -> Result<()> {
-        let page_size = buf.len();
+    fn get(&self, page_idx: usize, c: &mut Completion) -> Result<()> {
+        let page_size = c.buf.len();
         assert!(page_idx > 0);
         assert!(page_size >= 512);
         assert!(page_size <= 65536);
         assert!((page_size & (page_size - 1)) == 0);
         let pos = (page_idx - 1) * page_size;
-        self.file.pread(pos, buf)?;
+        self.file.pread(pos, c)?;
         Ok(())
     }
 }