GuestMemory: Add lifetimes to try_access()

With virtual memory, seemingly consecutive I/O virtual memory regions
may actually be fragmented across multiple pages in our userspace
mapping.  Existing `descriptor_utils::Reader::new()` (and `Writer`)
implementations (e.g. in virtiofsd or vm-virtio/virtio-queue) use
`GuestMemory::get_slice()` to turn guest memory address ranges into
valid slices in our address space; but with this fragmentation, it is
easily possible that a range no longer corresponds to a single slice.

To fix this, we can instead use `try_access()` to collect all slices,
but to do so, its region argument needs to have the correct lifetime so
we can collect the slices into a `Vec<_>` outside of the closure.

Signed-off-by: Hanna Czenczek <[email protected]>

Author: XanClic

src/guest_memory.rs

@@ -501,9 +501,9 @@ pub trait GuestMemory {
     /// - the error code returned by the callback 'f'
     /// - the size of the already handled data when encountering the first hole
     /// - the size of the already handled data when the whole range has been handled
-    fn try_access<F>(&self, count: usize, addr: GuestAddress, mut f: F) -> Result<usize>
+    fn try_access<'a, F>(&'a self, count: usize, addr: GuestAddress, mut f: F) -> Result<usize>
     where
-        F: FnMut(usize, usize, MemoryRegionAddress, &Self::R) -> Result<usize>,
+        F: FnMut(usize, usize, MemoryRegionAddress, &'a Self::R) -> Result<usize>,
     {
         let mut cur = addr;
         let mut total = 0;