fix: replace risky dma_buffer_as_vec implementations (#16829)

* dma_buffer_to_bytes

Signed-off-by: coldWater <forsaken628@gmail.com>

* fix

Signed-off-by: coldWater <forsaken628@gmail.com>

* Memory fitting

Signed-off-by: coldWater <forsaken628@gmail.com>

---------

Signed-off-by: coldWater <forsaken628@gmail.com>

Author: forsaken628

Cargo.lock

@@ -26,6 +26,7 @@ databend-common-exception = { workspace = true }
 async-backtrace = { workspace = true }
 async-trait = { workspace = true }
 borsh = { workspace = true }
+bytes = { workspace = true }
 bytesize = { workspace = true }
 chrono = { workspace = true }
 ctrlc = { workspace = true }

src/common/base/Cargo.toml

@@ -28,6 +28,7 @@ use std::path::Path;
 use std::ptr;
 use std::ptr::NonNull;
 
+use bytes::Bytes;
 use rustix::fs::OFlags;
 use tokio::fs::File;
 use tokio::io::AsyncSeekExt;
@@ -116,10 +117,6 @@ impl DmaAllocator {
             Layout::from_size_align(layout.size(), self.0.as_usize()).unwrap()
         }
     }
-
-    fn real_cap(&self, cap: usize) -> usize {
-        self.0.align_up(cap)
-    }
 }
 
 unsafe impl Allocator for DmaAllocator {
@@ -131,6 +128,10 @@ unsafe impl Allocator for DmaAllocator {
         Global {}.allocate_zeroed(self.real_layout(layout))
     }
 
+    unsafe fn deallocate(&self, ptr: std::ptr::NonNull<u8>, layout: Layout) {
+        Global {}.deallocate(ptr, self.real_layout(layout))
+    }
+
     unsafe fn grow(
         &self,
         ptr: NonNull<u8>,
@@ -157,20 +158,38 @@ unsafe impl Allocator for DmaAllocator {
         )
     }
 
-    unsafe fn deallocate(&self, ptr: std::ptr::NonNull<u8>, layout: Layout) {
-        Global {}.deallocate(ptr, self.real_layout(layout))
+    unsafe fn shrink(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        Global {}.shrink(
+            ptr,
+            self.real_layout(old_layout),
+            self.real_layout(new_layout),
+        )
     }
 }
 
 type DmaBuffer = Vec<u8, DmaAllocator>;
 
-pub fn dma_buffer_as_vec(mut buf: DmaBuffer) -> Vec<u8> {
-    let ptr = buf.as_mut_ptr();
-    let len = buf.len();
-    let cap = buf.allocator().real_cap(buf.capacity());
-    std::mem::forget(buf);
-
-    unsafe { Vec::from_raw_parts(ptr, len, cap) }
+pub fn dma_buffer_to_bytes(buf: DmaBuffer) -> Bytes {
+    if buf.is_empty() {
+        return Bytes::new();
+    }
+    let (ptr, len, cap, alloc) = buf.into_raw_parts_with_alloc();
+    // Memory fitting
+    let old_layout = Layout::from_size_align(cap, alloc.0.as_usize()).unwrap();
+    let new_layout = Layout::from_size_align(len, std::mem::align_of::<u8>()).unwrap();
+    let data = unsafe {
+        let p = Global {}
+            .shrink(NonNull::new(ptr).unwrap(), old_layout, new_layout)
+            .unwrap();
+        let cap = p.len();
+        Vec::from_raw_parts(p.cast().as_mut(), len, cap)
+    };
+    Bytes::from(data)
 }
 
 /// A `DmaFile` is similar to a `File`, but it is opened with the `O_DIRECT` file in order to
@@ -697,4 +716,28 @@ mod tests {
 
         let _ = std::fs::remove_file(filename);
     }
+
+    #[test]
+    fn test_dma_buffer_to_bytes() {
+        let want = (0..10_u8).collect::<Vec<_>>();
+        let alloc = DmaAllocator::new(Alignment::new(4096).unwrap());
+        let mut buf = DmaBuffer::with_capacity_in(3000, alloc);
+        buf.extend_from_slice(&want);
+
+        println!("{:?} {}", buf.as_ptr(), buf.capacity());
+        buf.shrink_to_fit();
+        println!("{:?} {}", buf.as_ptr(), buf.capacity());
+        buf.reserve(3000 - buf.capacity());
+        println!("{:?} {}", buf.as_ptr(), buf.capacity());
+
+        // let slice = buf.into_boxed_slice();
+        // println!("{:?}", slice.as_ptr());
+
+        let got = dma_buffer_to_bytes(buf);
+        println!("{:?}", got.as_ptr());
+        assert_eq!(&want, &got);
+
+        let buf = got.to_vec();
+        println!("{:?} {}", buf.as_ptr(), buf.capacity());
+    }
 }

src/common/base/src/base/dma.rs

@@ -28,7 +28,7 @@ mod take_mut;
 mod uniq_id;
 mod watch_notify;
 
-pub use dma::dma_buffer_as_vec;
+pub use dma::dma_buffer_to_bytes;
 pub use dma::dma_read_file;
 pub use dma::dma_read_file_range;
 pub use dma::dma_write_file_vectored;

src/common/base/src/base/mod.rs

@@ -25,6 +25,7 @@
 #![feature(slice_swap_unchecked)]
 #![feature(variant_count)]
 #![feature(ptr_alignment_type)]
+#![feature(vec_into_raw_parts)]
 
 pub mod base;
 pub mod containers;

src/common/base/src/lib.rs

@@ -20,8 +20,7 @@ use std::ops::Range;
 use std::sync::Arc;
 use std::time::Instant;
 
-use bytes::Bytes;
-use databend_common_base::base::dma_buffer_as_vec;
+use databend_common_base::base::dma_buffer_to_bytes;
 use databend_common_base::base::dma_read_file_range;
 use databend_common_base::base::Alignment;
 use databend_common_base::base::DmaWriteBuf;
@@ -277,7 +276,7 @@ impl Spiller {
                     None => {
                         let file_size = path.size();
                         let (buf, range) = dma_read_file_range(path, 0..file_size as u64).await?;
-                        Buffer::from(dma_buffer_as_vec(buf)).slice(range)
+                        Buffer::from(dma_buffer_to_bytes(buf)).slice(range)
                     }
                 }
             }
@@ -330,7 +329,7 @@ impl Spiller {
                 );
 
                 let (buf, range) = dma_read_file_range(path, 0..file_size as u64).await?;
-                Buffer::from(dma_buffer_as_vec(buf)).slice(range)
+                Buffer::from(dma_buffer_to_bytes(buf)).slice(range)
             }
             (Location::Local(path), Some(ref local)) => {
                 local
@@ -371,7 +370,7 @@ impl Spiller {
                 }
                 None => {
                     let (buf, range) = dma_read_file_range(path, data_range).await?;
-                    Buffer::from(dma_buffer_as_vec(buf)).slice(range)
+                    Buffer::from(dma_buffer_to_bytes(buf)).slice(range)
                 }
             },
             Location::Remote(loc) => self.operator.read_with(loc).range(data_range).await?,
@@ -410,7 +409,7 @@ impl Spiller {
         let buf = buf
             .into_data()
             .into_iter()
-            .map(|x| Bytes::from(dma_buffer_as_vec(x)))
+            .map(dma_buffer_to_bytes)
             .collect::<Buffer>();
         let written = buf.len();
         writer.write(buf).await?;