fix: Remove 4096B chunk restriction of read/write_volatile

Fixes a bug where GuestMemory::read_volatile_from and
GuestMemory::write_volatile_into would only copy data in chunks of at
most 4096 bytes from/into the underlying stream. The check removed in
this commit was errorneously copied from the read_from/write_into
functions, which use a temporary buffer to transfer data (and this
temporary buffer was capped to 4096 bytes).

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

CHANGELOG.md

@@ -5,6 +5,9 @@
 ### Added
 ### Changed
 ### Fixed
+- [[#279](https://github.com/rust-vmm/vm-memory/pull/279)] Remove restriction from `read_volatile_from` and `write_volatile_into`
+ that made it copy data it chunks of 4096.
+
 ### Removed
 ### Deprecated
 

src/guest_memory.rs

@@ -724,8 +724,6 @@ pub trait GuestMemory {
  // Check if something bad happened before doing unsafe things.
  assert!(offset <= count);
 
- let len = std::cmp::min(len, MAX_ACCESS_CHUNK);
-
  let mut vslice = region.get_slice(caddr, len)?;
 
  src.read_volatile(&mut vslice)
@@ -749,7 +747,6 @@ pub trait GuestMemory {
  // Check if something bad happened before doing unsafe things.
  assert!(offset <= count);
 
- let len = std::cmp::min(len, MAX_ACCESS_CHUNK);
  let vslice = region.get_slice(caddr, len)?;
 
  // For a non-RAM region, reading could have side effects, so we