do not backdoor-enable backend-bitmap in unittests

The bitmap backend implementation in vm_memory::bitmap::backend is only
exported if the backend-bitmap feature is enabled. However, compiling
the crate in test mode (e.g. `cargo test`), also unconditionally enables
it. This is weird, and actually causes problems: The bitmap backend code
depends on the libc crate, and this weird "enable unconditionally for
tests" behavior means we have to go through more trouble in Cargo.toml
to get the code to compile in some feature combinations, as not only do
we need to add the libc crate as a dependency of the backend-bitmap
feature, we also have to add it as a dev-dependency.

Add a #[cfg(feature = "backend-bitmap")] to the test module in
src/bitmap/mod.rs, as otherwise some of the functions will be warned
about being unused in some feature configurations.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

src/bitmap/mod.rs

@@ -6,14 +6,14 @@
 //! `GuestMemoryRegion` object, and the resulting bitmaps can then be aggregated to build the
 //! global view for an entire `GuestMemory` object.
 
-#[cfg(any(test, feature = "backend-bitmap"))]
+#[cfg(feature = "backend-bitmap")]
 mod backend;
 
 use std::fmt::Debug;
 
 use crate::{GuestMemory, GuestMemoryRegion};
 
-#[cfg(any(test, feature = "backend-bitmap"))]
+#[cfg(feature = "backend-bitmap")]
 pub use backend::{ArcSlice, AtomicBitmap, RefSlice};
 
 /// Trait implemented by types that support creating `BitmapSlice` objects.
@@ -117,6 +117,7 @@ pub type BS<'a, B> = <B as WithBitmapSlice<'a>>::S;
 pub type MS<'a, M> = BS<'a, <<M as GuestMemory>::R as GuestMemoryRegion>::B>;
 
 #[cfg(test)]
+#[cfg(feature = "backend-bitmap")]
 pub(crate) mod tests {
     use super::*;
 

src/mmap/mod.rs

@@ -489,6 +489,7 @@ mod tests {
     use super::*;
 
     use crate::bitmap::tests::test_guest_memory_and_region;
+    #[cfg(feature = "backend-bitmap")]
     use crate::bitmap::AtomicBitmap;
     use crate::GuestAddressSpace;
 
@@ -1363,6 +1364,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "backend-bitmap")]
     fn test_dirty_tracking() {
         test_guest_memory_and_region(|| {
             crate::GuestMemoryMmap::<AtomicBitmap>::from_ranges(&[(GuestAddress(0), 0x1_0000)])

src/mmap/unix.rs

@@ -443,6 +443,7 @@ mod tests {
     use std::sync::Arc;
     use vmm_sys_util::tempfile::TempFile;
 
+    #[cfg(feature = "backend-bitmap")]
     use crate::bitmap::AtomicBitmap;
 
     type MmapRegion = super::MmapRegion<()>;
@@ -535,6 +536,7 @@ mod tests {
 
     #[test]
     #[cfg(not(miri))] // Miri cannot mmap files
+    #[cfg(feature = "backend-bitmap")]
     fn test_mmap_region_build() {
         let a = Arc::new(TempFile::new().unwrap().into_file());
 
@@ -648,6 +650,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "backend-bitmap")]
     fn test_dirty_tracking() {
         // Using the `crate` prefix because we aliased `MmapRegion` to `MmapRegion<()>` for
         // the rest of the unit tests above.

src/volatile_memory.rs

@@ -1447,6 +1447,7 @@ mod tests {
 
     #[cfg(feature = "rawfd")]
     use std::fs::File;
+    #[cfg(feature = "backend-bitmap")]
     use std::mem::size_of_val;
     #[cfg(feature = "rawfd")]
     use std::path::Path;
@@ -1459,9 +1460,11 @@ mod tests {
     #[cfg(feature = "rawfd")]
     use vmm_sys_util::tempfile::TempFile;
 
+    #[cfg(feature = "backend-bitmap")]
     use crate::bitmap::tests::{
         check_range, range_is_clean, range_is_dirty, test_bytes, test_volatile_memory,
     };
+    #[cfg(feature = "backend-bitmap")]
     use crate::bitmap::{AtomicBitmap, RefSlice};
 
     const DEFAULT_PAGE_SIZE: NonZeroUsize = unsafe { NonZeroUsize::new_unchecked(0x1000) };
@@ -2132,6 +2135,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "backend-bitmap")]
     fn test_volatile_slice_dirty_tracking() {
         let val = 123u64;
         let dirty_offset = 0x1000;
@@ -2222,6 +2226,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "backend-bitmap")]
     fn test_volatile_ref_dirty_tracking() {
         let val = 123u64;
         let mut buf = vec![val];
@@ -2236,6 +2241,7 @@ mod tests {
         assert!(range_is_dirty(vref.bitmap(), 0, vref.len()));
     }
 
+    #[cfg(feature = "backend-bitmap")]
     fn test_volatile_array_ref_copy_from_tracking<T>(
         buf: &mut [T],
         index: usize,
@@ -2262,6 +2268,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "backend-bitmap")]
     fn test_volatile_array_ref_dirty_tracking() {
         let val = 123u64;
         let dirty_len = size_of_val(&val);