Struct RequestBuffers 

pub struct RequestBuffers<'a> { /* private fields */ }

An accessor for guest memory associated with a storage IO request.

Wraps a single [PagedRange] — a contiguous byte range scattered across guest pages — together with a GuestMemory reference and a read/write direction flag.

One range per RequestBuffers

Because PagedRange requires interior pages to be fully covered, a RequestBuffers can only describe memory regions where every page boundary between the first and last page is fully spanned. Two guest memory regions with arbitrary starting GPAs generally cannot be combined into one RequestBuffers.

When a device has multiple disjoint memory regions for a single IO (e.g., a virtio descriptor chain whose descriptors don’t align to page boundaries), options include:

• Issue separate IOs per region (only valid if each region is sector-aligned)
• Use a BounceBuffer to coalesce into one contiguous buffer
• Use multiple RequestBuffers with a multi-range disk backend API (not currently available)

Implementations

impl<'a> RequestBuffers<'a>

pub fn new( guest_memory: &'a GuestMemory, range: PagedRange<'a>, is_write: bool, ) -> Self

Creates a new request buffer from the given memory ranges.

pub fn is_empty(&self) -> bool

Returns true if the buffer is empty.

pub fn len(&self) -> usize

Return the total length of the buffers in bytes.

pub fn guest_memory(&self) -> &GuestMemory

Returns the guest memory accessor.

pub fn range(&self) -> PagedRange<'_>

Return the internal paged range.

pub fn is_aligned(&self, alignment: usize) -> bool

Returns whether the buffer is aligned to at least alignment bytes.

Checks three things (all must be multiples of alignment):

1. The byte offset into the first page (range.offset())
2. The total byte length (range.len())
3. The page size (4096) — always true for alignment ≤ 4096

When this returns false, disk backends that require aligned buffers (e.g., those using O_DIRECT or io_uring) must use a BounceBuffer to perform the IO.

Panics

Panics if alignment is not a power of two.

pub fn writer(&self) -> impl MemoryWrite + '_

Gets a memory writer for the buffers.

Returns an empty writer if the buffers are only available for read access.

pub fn reader(&self) -> impl MemoryRead + '_

Gets a memory reader for the buffers.

pub fn lock(&self, for_write: bool) -> Result<LockedIoBuffers, AccessError>

Locks the guest memory ranges described by this buffer and returns an object containing IoBuffers, suitable for executing asynchronous I/O operations.

pub fn subrange(&self, offset: usize, len: usize) -> Self

Returns a subrange of this set of buffers.

Panics if offset + len > self.len().

Trait Implementations

impl<'a> Clone for RequestBuffers<'a>

fn clone(&self) -> RequestBuffers<'a>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a> Debug for RequestBuffers<'a>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.