fix: ignore unsafe preconditions on debug

Latest rust from_raw_parts now ensures the ptr is valid.
This causes issues on write_zeroes where the iovec is actually
not valid and not used.
For now let's simply ignore this precondition check since the
iovec is not used but probably we ought to use fix this for
release as well, just in case.

Signed-off-by: Tiago Castro <tiagolobocastro@gmail.com>

src/bdev_io.rs

@@ -4,6 +4,7 @@ use std::{
     fmt::{Debug, Formatter},
     marker::PhantomData,
     os::raw::c_void,
+    ptr,
     ptr::NonNull,
     slice::{from_raw_parts, from_raw_parts_mut},
 };
@@ -40,7 +41,6 @@ pub trait AsIoVecs {
 /// # Generic Arguments
 ///
 /// * `BdevData`: TODO
-#[derive(Copy)]
 pub struct BdevIo<BdevData>
 where
     BdevData: BdevOps,
@@ -49,6 +49,8 @@ where
     inner: NonNull<spdk_bdev_io>,
     /// TODO
     _data: PhantomData<BdevData>,
+    #[cfg(debug_assertions)]
+    _no_iov: Vec<IoVec>,
 }
 
 impl<BdevData> BdevIo<BdevData>
@@ -114,10 +116,11 @@ where
     pub fn iovs(&self) -> &[IoVec] {
         unsafe {
             let bdev = self.as_ref().u.bdev;
-            std::slice::from_raw_parts(
-                bdev.iovs as *const IoVec,
-                bdev.iovcnt as usize,
-            )
+            #[cfg(debug_assertions)]
+            if bdev.iovs.is_null() {
+                return &self._no_iov;
+            }
+            from_raw_parts(bdev.iovs as *const IoVec, bdev.iovcnt as usize)
         }
     }
 
@@ -126,10 +129,7 @@ where
     pub fn iovs_mut(&self) -> &mut [IoVec] {
         unsafe {
             let bdev = self.as_ref().u.bdev;
-            std::slice::from_raw_parts_mut(
-                bdev.iovs as *mut IoVec,
-                bdev.iovcnt as usize,
-            )
+            from_raw_parts_mut(bdev.iovs as *mut IoVec, bdev.iovcnt as usize)
         }
     }
 
@@ -254,6 +254,8 @@ where
         BdevIo {
             inner: NonNull::new(bio).unwrap(),
             _data: Default::default(),
+            #[cfg(debug_assertions)]
+            _no_iov: vec![],
         }
     }
 
@@ -321,6 +323,8 @@ where
         Self {
             inner: self.inner,
             _data: Default::default(),
+            #[cfg(debug_assertions)]
+            _no_iov: vec![],
         }
     }
 }