WeakDmaFile was accidentally missing from exports

Also missing were default and new constructor methods.

glommio/src/io/dma_file.rs

@@ -880,7 +880,31 @@ pub struct WeakDmaFile {
     pollable: PollableStatus,
 }
 
+impl Default for WeakDmaFile {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl WeakDmaFile {
+    /// Creates an empty reference that will never upgrade.
+    pub fn new() -> WeakDmaFile {
+        Self {
+            file: WeakGlommioFile::new(),
+            o_direct_alignment: 0,
+            max_sectors_size: 0,
+            max_segment_size: 0,
+            pollable: PollableStatus::Pollable,
+        }
+    }
+
+    /// The number of strong references that still remain on the file.
+    /// If created via [Self::new], this will return 0.
+    pub fn strong_count(&self) -> usize {
+        self.file.strong_count()
+    }
+
+    /// Returns an `Option` containing ownership over the file if the file hasn't been closed yet, otherwise None.
     pub fn upgrade(&self) -> Option<OwnedDmaFile> {
         self.file.upgrade().map(|file| OwnedDmaFile {
             file,

glommio/src/io/glommio_file.rs

@@ -437,7 +437,7 @@ impl From<GlommioFile> for OwnedGlommioFile {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Default, Debug, Clone)]
 pub(crate) struct WeakGlommioFile {
     pub(crate) fd: AWeak<RawFd>,
     pub(crate) path: Option<PathBuf>,
@@ -447,6 +447,14 @@ pub(crate) struct WeakGlommioFile {
 }
 
 impl WeakGlommioFile {
+    pub(crate) fn new() -> Self {
+        Self::default()
+    }
+
+    pub(crate) fn strong_count(&self) -> usize {
+        self.fd.strong_count()
+    }
+
     pub(crate) fn upgrade(&self) -> Option<OwnedGlommioFile> {
         self.fd.upgrade().map(|fd| OwnedGlommioFile {
             fd: Some(fd),

glommio/src/io/mod.rs

@@ -162,7 +162,7 @@ pub use self::{
     },
     bulk_io::{IoVec, MergedBufferLimit, ReadAmplificationLimit, ReadManyResult},
     directory::Directory,
-    dma_file::{CloseResult, DmaFile, OwnedDmaFile},
+    dma_file::{CloseResult, DmaFile, OwnedDmaFile, WeakDmaFile},
     dma_file_stream::{
         DmaStreamReader, DmaStreamReaderBuilder, DmaStreamWriter, DmaStreamWriterBuilder,
     },