refactor: Stop using AsFd hack in MaybeBounce

We put the bounds as AsFd to work around limitations in vm-memory about
not implementing Read/WriteVolatile for &File and &mut File, but it
ended up just causing even more workarounds being required elsewhere
(vsock unittests, where AsFd cannot meaningfully be implemented for
mocks). So just bite the bullet and clone some files until vm-memory
gets some more impls.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

src/vmm/src/builder.rs

@@ -5,6 +5,7 @@
 
 use std::fmt::Debug;
 use std::io::{self};
+use std::os::fd::AsFd;
 use std::os::unix::fs::MetadataExt;
 #[cfg(feature = "gdb")]
 use std::sync::mpsc;
@@ -274,7 +275,7 @@ pub fn build_microvm_for_boot(
     }
 
     let entry_point = load_kernel(
-        MaybeBounce::new(&boot_config.kernel_file, secret_free),
+        MaybeBounce::new(boot_config.kernel_file.try_clone().unwrap(), secret_free),
         vmm.vm.guest_memory(),
     )?;
     let initrd = match &boot_config.initrd_file {
@@ -286,7 +287,7 @@ pub fn build_microvm_for_boot(
 
             Some(InitrdConfig::from_reader(
                 vmm.vm.guest_memory(),
-                MaybeBounce::new(initrd_file, secret_free),
+                MaybeBounce::new(initrd_file.as_fd(), secret_free),
                 u64_to_usize(size),
             )?)
         }

src/vmm/src/vstate/memory.rs

@@ -8,7 +8,7 @@
 use std::fs::File;
 use std::io::{Read, Seek, SeekFrom, Write};
 use std::mem::ManuallyDrop;
-use std::os::fd::{AsFd, AsRawFd};
+use std::os::fd::AsRawFd;
 use std::ptr::null_mut;
 use std::sync::Arc;
 
@@ -106,7 +106,7 @@ impl<T, const N: usize> MaybeBounce<T, N> {
 }
 
 // FIXME: replace AsFd with ReadVolatile once &File: ReadVolatile in vm-memory.
-impl<T: Read + AsFd, const N: usize> ReadVolatile for MaybeBounce<T, N> {
+impl<T: ReadVolatile, const N: usize> ReadVolatile for MaybeBounce<T, N> {
     fn read_volatile<B: BitmapSlice>(
         &mut self,
         buf: &mut VolatileSlice<B>,
@@ -121,8 +121,7 @@ impl<T: Read + AsFd, const N: usize> ReadVolatile for MaybeBounce<T, N> {
                 let how_much = buf.len().min(bbuf.len());
                 let n = self
                     .target
-                    .read(&mut bbuf[..how_much])
-                    .map_err(VolatileMemoryError::IOError)?;
+                    .read_volatile(&mut VolatileSlice::from(&mut bbuf[..how_much]))?;
                 buf.copy_from(&bbuf[..n]);
 
                 buf = buf.offset(n)?;
@@ -135,12 +134,12 @@ impl<T: Read + AsFd, const N: usize> ReadVolatile for MaybeBounce<T, N> {
 
             Ok(total)
         } else {
-            self.target.as_fd().read_volatile(buf)
+            self.target.read_volatile(buf)
         }
     }
 }
 
-impl<T: Write + AsFd, const N: usize> WriteVolatile for MaybeBounce<T, N> {
+impl<T: WriteVolatile, const N: usize> WriteVolatile for MaybeBounce<T, N> {
     fn write_volatile<B: BitmapSlice>(
         &mut self,
         buf: &VolatileSlice<B>,
@@ -155,8 +154,7 @@ impl<T: Write + AsFd, const N: usize> WriteVolatile for MaybeBounce<T, N> {
                 let how_much = buf.copy_to(bbuf);
                 let n = self
                     .target
-                    .write(&bbuf[..how_much])
-                    .map_err(VolatileMemoryError::IOError)?;
+                    .write_volatile(&VolatileSlice::from(&mut bbuf[..how_much]))?;
                 buf = buf.offset(n)?;
                 total += n;
 
@@ -167,7 +165,7 @@ impl<T: Write + AsFd, const N: usize> WriteVolatile for MaybeBounce<T, N> {
 
             Ok(total)
         } else {
-            self.target.as_fd().write_volatile(buf)
+            self.target.write_volatile(buf)
         }
     }
 }
@@ -652,6 +650,7 @@ mod tests {
 
     use std::collections::HashMap;
     use std::io::{Read, Seek};
+    use std::os::fd::AsFd;
 
     use itertools::Itertools;
     use vmm_sys_util::tempfile::TempFile;
@@ -1030,13 +1029,13 @@ mod tests {
 
         let mut data = (0..=255).collect_vec();
 
-        MaybeBounce::new(file_direct.as_file(), false)
+        MaybeBounce::new(file_direct.as_file().as_fd(), false)
             .write_all_volatile(&VolatileSlice::from(data.as_mut_slice()))
             .unwrap();
-        MaybeBounce::new(file_bounced.as_file(), true)
+        MaybeBounce::new(file_bounced.as_file().as_fd(), true)
             .write_all_volatile(&VolatileSlice::from(data.as_mut_slice()))
             .unwrap();
-        MaybeBounce::<_, 7>::new_persistent(file_persistent_bounced.as_file(), true)
+        MaybeBounce::<_, 7>::new_persistent(file_persistent_bounced.as_file().as_fd(), true)
             .write_all_volatile(&VolatileSlice::from(data.as_mut_slice()))
             .unwrap();
 
@@ -1051,13 +1050,13 @@ mod tests {
             .seek(SeekFrom::Start(0))
             .unwrap();
 
-        MaybeBounce::new(file_direct.as_file(), false)
+        MaybeBounce::new(file_direct.as_file().as_fd(), false)
             .read_exact_volatile(&mut VolatileSlice::from(data_direct.as_mut_slice()))
             .unwrap();
-        MaybeBounce::new(file_bounced.as_file(), true)
+        MaybeBounce::new(file_bounced.as_file().as_fd(), true)
             .read_exact_volatile(&mut VolatileSlice::from(data_bounced.as_mut_slice()))
             .unwrap();
-        MaybeBounce::<_, 7>::new_persistent(file_persistent_bounced.as_file(), true)
+        MaybeBounce::<_, 7>::new_persistent(file_persistent_bounced.as_file().as_fd(), true)
             .read_exact_volatile(&mut VolatileSlice::from(
                 data_persistent_bounced.as_mut_slice(),
             ))

src/vmm/src/vstate/vm.rs

@@ -8,7 +8,7 @@
 use std::collections::HashMap;
 use std::fs::{File, OpenOptions};
 use std::io::Write;
-use std::os::fd::FromRawFd;
+use std::os::fd::{AsFd, FromRawFd};
 use std::path::Path;
 use std::sync::Arc;
 
@@ -465,9 +465,10 @@ impl Vm {
                     .guest_memory()
                     .iter()
                     .any(|r| r.inner().guest_memfd != 0);
+                let mut maybe_bounce = MaybeBounce::new(file.as_fd(), secret_hidden);
                 self.guest_memory()
-                    .dump(&mut MaybeBounce::new(&file, secret_hidden))
-                    .and_then(|_| self.swiotlb_regions().dump(&mut file))?;
+                    .dump(&mut maybe_bounce)
+                    .and_then(|_| self.swiotlb_regions().dump(&mut maybe_bounce))?;
                 self.reset_dirty_bitmap();
                 self.guest_memory().reset_dirty();
             }