block: Implement synchronous I/O engine for Flat VMDK

Implements synchronous I/O engine for flat VMDK backend.
It uses an extent aware worker to map each request
to one or more backing extents. The implementation supports extents
opened with O_DIRECT using AlignedFile.

Async backends of io_uring and AIO are unimplemented because
requests spanning extents cannot be submitted with one fd + offset.

Signed-off-by: Sumedh Alok Sharma <sumsharma@microsoft.com>

block/src/formats/vmdk/engine_sync.rs

@@ -0,0 +1,293 @@
+// Copyright © 2026, Microsoft Corporation
+//
+// SPDX-License-Identifier: Apache-2.0
+
+use std::os::unix::fs::FileExt;
+use std::sync::Arc;
+use std::{cmp, io};
+
+use vmm_sys_util::eventfd::EventFd;
+
+use crate::AlignedFile;
+use crate::async_io::{
+    AsyncIo, AsyncIoCompletion, AsyncIoError, AsyncIoOperation, AsyncIoResult, CompletionCommon,
+};
+use crate::formats::vmdk::flat::{ExtentAccess, VmdkExtent};
+
+/// Synchronous, extent-aware I/O worker for flat VMDK images.
+///
+/// Maps each guest I/O request to one or more backing extents.
+///
+/// Async backends (io_uring/AIO) are not supported.
+pub(crate) struct FlatVmdkSync {
+    extents: Arc<Vec<VmdkExtent>>,
+    size: u64,
+    completions: CompletionCommon,
+}
+
+impl FlatVmdkSync {
+    pub fn new(extents: Arc<Vec<VmdkExtent>>, size: u64) -> Self {
+        FlatVmdkSync {
+            extents,
+            size,
+            completions: CompletionCommon::new(),
+        }
+    }
+
+    // Returns the extent containing virtual `offset`, or `None` if out of range.
+    fn extent_at(&self, offset: u64) -> Option<&VmdkExtent> {
+        self.extents
+            .iter()
+            .find(|e| offset >= e.virtual_start && offset < e.virtual_start + e.length)
+    }
+
+    fn check_access(&self, start: u64, total: u64, is_read: bool) -> io::Result<()> {
+        let end = start + total;
+        let mut cur = start;
+        while cur < end {
+            let extent = self.extent_at(cur).ok_or_else(|| {
+                io::Error::new(io::ErrorKind::InvalidData, "offset outside any VMDK extent")
+            })?;
+            match extent.access {
+                ExtentAccess::NoAccess => {
+                    return Err(io::Error::new(
+                        io::ErrorKind::PermissionDenied,
+                        format!("VMDK extent at offset {cur} is NOACCESS; request rejected"),
+                    ));
+                }
+                ExtentAccess::ReadOnly if !is_read => {
+                    return Err(io::Error::new(
+                        io::ErrorKind::PermissionDenied,
+                        format!("write to read-only VMDK extent at offset {cur} rejected"),
+                    ));
+                }
+                _ => {}
+            }
+            cur = extent.virtual_start + extent.length;
+        }
+        Ok(())
+    }
+
+    // Reads or writes a single contiguous segment of one extent through the
+    // extent's `AlignedFile`.
+    fn segment_io(
+        file: &AlignedFile,
+        file_offset: u64,
+        op: &mut AsyncIoOperation,
+        buf_start: usize,
+        seg_len: usize,
+        is_read: bool,
+    ) -> io::Result<usize> {
+        // O_DIRECT unaligned
+        if file.alignment() != 0 {
+            return if is_read {
+                file.read_unaligned(file_offset, seg_len, |data| {
+                    op.write_bytes_at(buf_start, data)
+                })
+            } else {
+                file.write_unaligned(file_offset, seg_len, |data| {
+                    op.read_bytes_at(buf_start, data)
+                })
+            };
+        }
+
+        // Aligned & Buffered
+        let mut buf = vec![0u8; seg_len];
+        let mut done = 0usize;
+        if is_read {
+            while done < seg_len {
+                match file.read_at(&mut buf[done..], file_offset + done as u64) {
+                    Ok(0) => break, // EOF: nothing more to read
+                    Ok(n) => done += n,
+                    Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
+                    Err(e) => return Err(e),
+                }
+            }
+            op.write_bytes_at(buf_start, &buf[..done])?;
+            Ok(done)
+        } else {
+            op.read_bytes_at(buf_start, &mut buf)?;
+            while done < seg_len {
+                match file.write_at(&buf[done..], file_offset + done as u64) {
+                    Ok(0) => break, // no progress: avoid spinning forever
+                    Ok(n) => done += n,
+                    Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
+                    Err(e) => return Err(e),
+                }
+            }
+            Ok(done)
+        }
+    }
+
+    // Single-extent path: the whole request lives in `extent`.
+    //
+    // The guest iovecs are handed to `AlignedFile::{read,write}_vectored_at`
+    fn single_extent_io(
+        &self,
+        extent: &VmdkExtent,
+        op: &mut AsyncIoOperation,
+    ) -> io::Result<usize> {
+        let file = extent.file.as_ref().ok_or_else(|| {
+            io::Error::new(
+                io::ErrorKind::PermissionDenied,
+                "VMDK extent is not accessible",
+            )
+        })?;
+        let file_offset = extent.file_base_offset + (op.offset() as u64 - extent.virtual_start);
+        let iovecs = op.iovecs();
+
+        // SAFETY: the iovec buffers are owned by `op` and remain valid for the
+        // duration of this call.
+        unsafe {
+            if op.is_read() {
+                file.read_vectored_at(iovecs, file_offset)
+            } else {
+                file.write_vectored_at(iovecs, file_offset)
+            }
+        }
+    }
+
+    // Slow path: the request straddles >= 2 extents.
+    //
+    // A single guest request here maps onto several different backing files,
+    // Every segment goes through `segment_io` regardless of
+    // alignment.
+    fn spanning_io(&self, op: &mut AsyncIoOperation) -> io::Result<usize> {
+        let start = op.offset() as u64;
+        let total = op.total_len() as u64;
+        let is_read = op.is_read();
+
+        let mut done: u64 = 0;
+        while done < total {
+            let cur = start + done;
+            let extent = self.extent_at(cur).ok_or_else(|| {
+                io::Error::new(io::ErrorKind::InvalidData, "offset outside any VMDK extent")
+            })?;
+            let extent_end = extent.virtual_start + extent.length;
+            // Bytes handled in this extent before reaching its boundary.
+            let seg_len = cmp::min(total - done, extent_end - cur) as usize;
+            let file = extent.file.as_ref().ok_or_else(|| {
+                io::Error::new(
+                    io::ErrorKind::PermissionDenied,
+                    "VMDK extent is not accessible",
+                )
+            })?;
+            let file_offset = extent.file_base_offset + (cur - extent.virtual_start);
+
+            let n = Self::segment_io(file, file_offset, op, done as usize, seg_len, is_read)?;
+            done += n as u64;
+            if n < seg_len {
+                break; // short read/write
+            }
+        }
+
+        Ok(done as usize)
+    }
+}
+
+impl AsyncIo for FlatVmdkSync {
+    fn notifier(&self) -> &EventFd {
+        self.completions.notifier()
+    }
+
+    fn submit_data_operation(&mut self, mut op: AsyncIoOperation) -> AsyncIoResult<()> {
+        let start = op.offset() as u64;
+        let total = op.total_len() as u64;
+        let is_read = op.is_read();
+
+        // Bounds check against the virtual disk size (overflow-safe: `start`
+        // is checked before subtracting it from `size`).
+        if start > self.size || total > self.size - start {
+            let error = io::Error::new(
+                io::ErrorKind::InvalidData,
+                format!(
+                    "VMDK request [{start}, {}) exceeds virtual size {}",
+                    start + total,
+                    self.size
+                ),
+            );
+            return Err(if is_read {
+                AsyncIoError::ReadVectored(error)
+            } else {
+                AsyncIoError::WriteVectored(error)
+            });
+        }
+
+        // Reject the request up front if any extent it touches forbids it:
+        // NOACCESS extents reject all I/O.
+        if total != 0
+            && let Err(error) = self.check_access(start, total, is_read)
+        {
+            return Err(if is_read {
+                AsyncIoError::ReadVectored(error)
+            } else {
+                AsyncIoError::WriteVectored(error)
+            });
+        }
+
+        let result = if total == 0 {
+            Ok(0)
+        } else if let Some(extent) = self.extent_at(start) {
+            if start + total <= extent.virtual_start + extent.length {
+                // Entire request fits in one extent
+                self.single_extent_io(extent, &mut op)
+            } else {
+                // Request crosses an extent boundary
+                self.spanning_io(&mut op)
+            }
+        } else {
+            Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "offset outside any VMDK extent",
+            ))
+        };
+
+        let bytes = result.map_err(|e| {
+            if is_read {
+                AsyncIoError::ReadVectored(e)
+            } else {
+                AsyncIoError::WriteVectored(e)
+            }
+        })?;
+
+        self.completions
+            .complete(AsyncIoCompletion::from_operation(op, bytes as i32));
+        Ok(())
+    }
+
+    fn fsync(&mut self, user_data: Option<u64>) -> AsyncIoResult<()> {
+        // Flush every extent: a single guest flush must durably persist data
+        // that may have been written across multiple extent files.
+        for extent in self.extents.iter() {
+            // Skip NoAccess extents, which have no open file.
+            if let Some(file) = extent.file.as_ref() {
+                file.sync_all().map_err(AsyncIoError::Fsync)?;
+            }
+        }
+
+        if let Some(user_data) = user_data {
+            self.completions
+                .complete(AsyncIoCompletion::new(user_data, 0, None));
+        }
+
+        Ok(())
+    }
+
+    fn next_completed_request(&mut self) -> Option<AsyncIoCompletion> {
+        self.completions.next_completed()
+    }
+
+    fn punch_hole(&mut self, _offset: u64, _length: u64, _user_data: u64) -> AsyncIoResult<()> {
+        // Flat VMDK is not sparse-capable (see `SparseCapable` impl), so this
+        // should never be negotiated by the guest.
+        Err(AsyncIoError::PunchHole(io::Error::other(
+            "punch_hole not supported for flat VMDK",
+        )))
+    }
+
+    fn write_zeroes(&mut self, _offset: u64, _length: u64, _user_data: u64) -> AsyncIoResult<()> {
+        Err(AsyncIoError::WriteZeroes(io::Error::other(
+            "write_zeroes not supported for flat VMDK",
+        )))
+    }
+}

block/src/formats/vmdk/flat.rs

@@ -5,8 +5,6 @@
 //! Flat VMDK extent layout: opens the data extents referenced by the
 //! descriptor and maps the virtual disk onto them.
 
-#![allow(dead_code)]
-
 use std::ffi::{CString, OsStr};
 use std::fs::{File, OpenOptions};
 use std::io;
@@ -19,7 +17,7 @@ use std::sync::Arc;
 use log::warn;
 
 use crate::formats::vmdk::descriptor::VmdkDescriptor;
-use crate::{AlignedFile, DiskTopology};
+use crate::{AlignedFile, DiskTopology, query_device_size};
 
 const VMDK_SECTOR_SIZE: u64 = 512;
 
@@ -346,18 +344,16 @@ impl FlatVmdk {
         Arc::clone(&self.extents)
     }
 
-    /// Host allocation size: the sum of every opened extent file's size.
-    /// `NoAccess` extents contribute 0 to the total.
+    /// Host allocation size: the sum of every opened extent's actually
+    /// allocated storage (`st_blocks * 512` for regular files, device size for
+    /// block devices), so sparse extents are reported correctly. `NoAccess`
+    /// extents (no open file) contribute 0, as does any extent whose size
+    /// cannot be queried.
     pub fn physical_block_size(&self) -> u64 {
         self.extents
             .iter()
-            .map(|extent| {
-                extent
-                    .file
-                    .as_ref()
-                    .and_then(|f| f.metadata().ok())
-                    .map_or(0, |m| m.len())
-            })
+            .filter_map(|extent| extent.file.as_ref())
+            .map(|f| query_device_size(f.file()).map_or(0, |(_, physical)| physical))
             .sum()
     }
 

block/src/formats/vmdk/mod.rs

@@ -1,4 +1,4 @@
-// Copyright 2026 The Cloud Hypervisor Authors. All rights reserved.
+// Copyright © 2026, Microsoft Corporation
 //
 // SPDX-License-Identifier: Apache-2.0
 
@@ -8,6 +8,377 @@
 //! synchronous, extent-aware I/O.
 
 mod descriptor;
+mod engine_sync;
 mod flat;
 
+use std::fs::File;
+use std::io;
+use std::os::unix::io::AsRawFd;
+use std::path::Path;
+
 pub use descriptor::{has_descriptor_header, is_flat_vmdk};
+
+use self::engine_sync::FlatVmdkSync;
+use self::flat::FlatVmdk;
+use crate::async_io::{AsyncIo, BorrowedDiskFd, DiskFileError};
+use crate::error::{BlockError, BlockErrorKind, BlockResult, ErrorOp};
+use crate::{DiskTopology, disk_file};
+
+#[derive(Debug)]
+pub struct VmdkDisk {
+    inner: FlatVmdk,
+}
+
+impl VmdkDisk {
+    /// Builds a Flat VMDK disk backend.
+    pub fn new(file: File, path: &Path, direct: bool) -> Result<Self, BlockError> {
+        let inner = FlatVmdk::new(file, path, direct)?;
+        Ok(VmdkDisk { inner })
+    }
+}
+
+impl disk_file::DiskSize for VmdkDisk {
+    fn logical_size(&self) -> BlockResult<u64> {
+        Ok(self.inner.virtual_block_size())
+    }
+}
+
+impl disk_file::PhysicalSize for VmdkDisk {
+    fn physical_size(&self) -> BlockResult<u64> {
+        Ok(self.inner.physical_block_size())
+    }
+}
+
+// Expose the descriptor file's fd for advisory image locking.
+impl disk_file::DiskFd for VmdkDisk {
+    fn fd(&self) -> BorrowedDiskFd<'_> {
+        BorrowedDiskFd::new(self.inner.as_raw_fd())
+    }
+}
+
+impl disk_file::Geometry for VmdkDisk {
+    fn topology(&self) -> DiskTopology {
+        self.inner.topology()
+    }
+}
+
+impl disk_file::SparseCapable for VmdkDisk {}
+
+// Flat VMDK keeps no in-memory format metadata, so no-op.
+impl disk_file::MetadataSync for VmdkDisk {}
+
+impl disk_file::Resizable for VmdkDisk {
+    fn resize(&mut self, _size: u64) -> BlockResult<()> {
+        Err(BlockError::new(
+            BlockErrorKind::UnsupportedFeature,
+            DiskFileError::ResizeError(io::Error::other("resize not supported for flat VMDK")),
+        )
+        .with_op(ErrorOp::Resize))
+    }
+}
+
+impl disk_file::DiskFile for VmdkDisk {}
+
+impl disk_file::AsyncDiskFile for VmdkDisk {
+    fn try_clone(&self) -> BlockResult<Box<dyn disk_file::AsyncDiskFile>> {
+        Ok(Box::new(VmdkDisk {
+            inner: self.inner.clone(),
+        }))
+    }
+
+    fn create_async_io(&self, ring_depth: u32) -> BlockResult<Box<dyn AsyncIo>> {
+        // VMDK provides a synchronous, extent-aware worker, so the io_uring ring
+        // depth is unused here.
+        let _ = ring_depth;
+
+        Ok(Box::new(FlatVmdkSync::new(
+            self.inner.extents(),
+            self.inner.virtual_block_size(),
+        )))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io::Write;
+    use std::os::unix::io::AsRawFd;
+    use std::path::PathBuf;
+
+    use vmm_sys_util::tempdir::TempDir;
+
+    use super::*;
+    use crate::disk_file::{AsyncDiskFile, DiskFd, DiskSize, PhysicalSize, Resizable};
+
+    const SECTOR: u64 = 512;
+
+    // Builds a flat VMDK in `dir`: a descriptor plus one backing data file per
+    // extent. When `allocate` is true the extent files are filled with real
+    // blocks (fixed / pre-allocated layout used in practice), otherwise they
+    // are created sparse via `set_len` (declared length but no allocated
+    // blocks). `extents` entries are (filename, access, sectors). Returns the
+    // descriptor path.
+    fn build_flat_vmdk(
+        dir: &Path,
+        create_type: &str,
+        extents: &[(&str, &str, u64)],
+        allocate: bool,
+    ) -> PathBuf {
+        let mut desc = String::from("# Disk DescriptorFile\n");
+        desc.push_str("version=1\n");
+        desc.push_str("CID=fffffffe\n");
+        desc.push_str("parentCID=ffffffff\n");
+        desc.push_str(&format!("createType={create_type}\n"));
+        desc.push_str("# Extent description\n");
+
+        for (filename, access, sectors) in extents {
+            let mut data = File::create(dir.join(filename)).unwrap();
+            if allocate {
+                data.write_all(&vec![0u8; (sectors * SECTOR) as usize])
+                    .unwrap();
+            } else {
+                data.set_len(sectors * SECTOR).unwrap();
+            }
+            data.sync_all().unwrap();
+            desc.push_str(&format!("{access} {sectors} FLAT \"{filename}\"\n"));
+        }
+
+        desc.push_str("# The Disk Data Base\n");
+        desc.push_str("ddb.adapterType = \"ide\"\n");
+
+        let desc_path = dir.join("disk.vmdk");
+        let mut df = File::create(&desc_path).unwrap();
+        df.write_all(desc.as_bytes()).unwrap();
+        df.sync_all().unwrap();
+        desc_path
+    }
+
+    // Sparse extents.
+    fn write_flat_vmdk(dir: &Path, create_type: &str, extents: &[(&str, &str, u64)]) -> PathBuf {
+        build_flat_vmdk(dir, create_type, extents, false)
+    }
+
+    // Fully pre-allocated extents.
+    fn write_flat_vmdk_allocated(
+        dir: &Path,
+        create_type: &str,
+        extents: &[(&str, &str, u64)],
+    ) -> PathBuf {
+        build_flat_vmdk(dir, create_type, extents, true)
+    }
+
+    fn open_descriptor(path: &Path) -> File {
+        File::open(path).unwrap()
+    }
+
+    // Writes a descriptor referencing `extent_lines` verbatim (no backing data
+    // files are created). Used to exercise `FlatVmdk::new`'s per-extent
+    // validation, whose zero-size/overflow checks all run before an extent file
+    // would be opened.
+    fn write_descriptor(dir: &Path, create_type: &str, extent_lines: &[&str]) -> PathBuf {
+        let mut desc = String::from("# Disk DescriptorFile\n");
+        desc.push_str("version=1\n");
+        desc.push_str("CID=fffffffe\n");
+        desc.push_str("parentCID=ffffffff\n");
+        desc.push_str(&format!("createType={create_type}\n"));
+        desc.push_str("# Extent description\n");
+        for line in extent_lines {
+            desc.push_str(line);
+            desc.push('\n');
+        }
+        desc.push_str("# The Disk Data Base\n");
+        desc.push_str("ddb.adapterType = \"ide\"\n");
+
+        let desc_path = dir.join("disk.vmdk");
+        let mut df = File::create(&desc_path).unwrap();
+        df.write_all(desc.as_bytes()).unwrap();
+        df.sync_all().unwrap();
+        desc_path
+    }
+
+    #[test]
+    fn logical_and_physical_size_single_extent() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-test").unwrap();
+        let path = write_flat_vmdk(
+            dir.as_path(),
+            "monolithicFlat",
+            &[("disk-flat.vmdk", "RW", 2048)],
+        );
+        let disk = VmdkDisk::new(open_descriptor(&path), &path, false).unwrap();
+
+        assert_eq!(disk.logical_size().unwrap(), 2048 * SECTOR);
+        // The extent is created sparse (`set_len`), so no blocks are allocated
+        // and the `st_blocks`-based physical size is 0.
+        assert_eq!(disk.physical_size().unwrap(), 0);
+    }
+
+    #[test]
+    fn logical_size_sums_multiple_extents() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-test").unwrap();
+        let path = write_flat_vmdk(
+            dir.as_path(),
+            "twoGbMaxExtentFlat",
+            &[("s001.vmdk", "RW", 2048), ("s002.vmdk", "RW", 1024)],
+        );
+        let disk = VmdkDisk::new(open_descriptor(&path), &path, false).unwrap();
+
+        assert_eq!(disk.logical_size().unwrap(), (2048 + 1024) * SECTOR);
+        // Sparse extents: no blocks are allocated, so physical size is 0.
+        assert_eq!(disk.physical_size().unwrap(), 0);
+    }
+
+    #[test]
+    fn physical_size_matches_fully_allocated_extents() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-test").unwrap();
+        let path = write_flat_vmdk_allocated(
+            dir.as_path(),
+            "twoGbMaxExtentFlat",
+            &[("s001.vmdk", "RW", 2048), ("s002.vmdk", "RW", 1024)],
+        );
+        let disk = VmdkDisk::new(open_descriptor(&path), &path, false).unwrap();
+
+        // Fully pre-allocated extents: host allocation (st_blocks) equals the
+        // declared logical size.
+        assert_eq!(disk.logical_size().unwrap(), (2048 + 1024) * SECTOR);
+        assert_eq!(disk.physical_size().unwrap(), (2048 + 1024) * SECTOR);
+    }
+
+    #[test]
+    fn fd_exposes_descriptor_file() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-test").unwrap();
+        let path = write_flat_vmdk(
+            dir.as_path(),
+            "monolithicFlat",
+            &[("disk-flat.vmdk", "RW", 64)],
+        );
+        let file = open_descriptor(&path);
+        let expected = file.as_raw_fd();
+
+        let disk = VmdkDisk::new(file, &path, false).unwrap();
+
+        assert_eq!(disk.fd().as_raw_fd(), expected);
+    }
+
+    #[test]
+    fn resize_is_unsupported() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-test").unwrap();
+        let path = write_flat_vmdk(
+            dir.as_path(),
+            "monolithicFlat",
+            &[("disk-flat.vmdk", "RW", 64)],
+        );
+        let mut disk = VmdkDisk::new(open_descriptor(&path), &path, false).unwrap();
+
+        let err = disk.resize(4096).unwrap_err();
+        assert_eq!(err.kind(), BlockErrorKind::UnsupportedFeature);
+    }
+
+    #[test]
+    fn try_clone_preserves_size() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-test").unwrap();
+        let path = write_flat_vmdk(
+            dir.as_path(),
+            "monolithicFlat",
+            &[("disk-flat.vmdk", "RW", 2048)],
+        );
+        let disk = VmdkDisk::new(open_descriptor(&path), &path, false).unwrap();
+
+        let cloned = disk.try_clone().unwrap();
+        assert_eq!(cloned.logical_size().unwrap(), disk.logical_size().unwrap());
+    }
+
+    #[test]
+    fn create_async_io_builds_worker() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-test").unwrap();
+        let path = write_flat_vmdk(
+            dir.as_path(),
+            "monolithicFlat",
+            &[("disk-flat.vmdk", "RW", 2048)],
+        );
+        let disk = VmdkDisk::new(open_descriptor(&path), &path, false).unwrap();
+
+        // Ring depth is ignored by the synchronous VMDK worker.
+        disk.create_async_io(0).unwrap();
+    }
+
+    #[test]
+    fn create_async_io_supports_multi_extent() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-test").unwrap();
+        let path = write_flat_vmdk(
+            dir.as_path(),
+            "twoGbMaxExtentFlat",
+            &[("s001.vmdk", "RW", 2048), ("s002.vmdk", "RW", 2048)],
+        );
+        let disk = VmdkDisk::new(open_descriptor(&path), &path, false).unwrap();
+
+        disk.create_async_io(32).unwrap();
+    }
+
+    #[test]
+    fn new_rejects_zero_sector_extent() {
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-zero-test").unwrap();
+        let path = write_descriptor(
+            dir.as_path(),
+            "monolithicFlat",
+            &["RW 0 FLAT \"disk-flat.vmdk\""],
+        );
+
+        let err = FlatVmdk::new(open_descriptor(&path), &path, false).unwrap_err();
+        assert_eq!(err.kind(), io::ErrorKind::InvalidData);
+    }
+
+    #[test]
+    fn new_rejects_extent_size_overflow() {
+        // size_in_sectors * 512 must fit in a u64.
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-ovf-size-test").unwrap();
+        let line = format!("RW {} FLAT \"disk-flat.vmdk\"", u64::MAX);
+        let path = write_descriptor(dir.as_path(), "monolithicFlat", &[line.as_str()]);
+
+        let err = FlatVmdk::new(open_descriptor(&path), &path, false).unwrap_err();
+        assert_eq!(err.kind(), io::ErrorKind::InvalidData);
+    }
+
+    #[test]
+    fn new_rejects_extent_file_offset_overflow() {
+        // The offset * 512 must fit in a u64.
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-ovf-offset-test").unwrap();
+        let line = format!("RW 1 FLAT \"disk-flat.vmdk\" {}", u64::MAX);
+        let path = write_descriptor(dir.as_path(), "monolithicFlat", &[line.as_str()]);
+
+        let err = FlatVmdk::new(open_descriptor(&path), &path, false).unwrap_err();
+        assert_eq!(err.kind(), io::ErrorKind::InvalidData);
+    }
+
+    #[test]
+    fn new_rejects_extent_file_range_overflow() {
+        // Each of offset*512 and size*512 fits in a u64, but their sum (the last
+        // byte the extent addresses in its backing file) overflows.
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-ovf-range-test").unwrap();
+        // offset_in_sectors = floor(u64::MAX / 512) => offset bytes = u64::MAX -
+        // 511, size 1 sector (512 bytes) pushes the end one byte past u64::MAX.
+        let offset = u64::MAX / 512;
+        let line = format!("RW 1 FLAT \"disk-flat.vmdk\" {offset}");
+        let path = write_descriptor(dir.as_path(), "monolithicFlat", &[line.as_str()]);
+
+        let err = FlatVmdk::new(open_descriptor(&path), &path, false).unwrap_err();
+        assert_eq!(err.kind(), io::ErrorKind::InvalidData);
+    }
+
+    #[test]
+    fn new_rejects_total_virtual_size_overflow() {
+        // Two extents whose individual lengths fit in a u64 but whose running
+        // sum (the total virtual disk size) overflows. size = 2^55 - 1 =>
+        // length = 2^64 - 512, two of them overflow the total.
+        let dir = TempDir::new_with_prefix("/tmp/vmdk-ovf-total-test").unwrap();
+        let size = (1u64 << 55) - 1;
+        let l1 = format!("NOACCESS {size} FLAT \"s001.vmdk\"");
+        let l2 = format!("NOACCESS {size} FLAT \"s002.vmdk\"");
+        let path = write_descriptor(
+            dir.as_path(),
+            "twoGbMaxExtentFlat",
+            &[l1.as_str(), l2.as_str()],
+        );
+
+        let err = FlatVmdk::new(open_descriptor(&path), &path, false).unwrap_err();
+        assert_eq!(err.kind(), io::ErrorKind::InvalidData);
+    }
+}