virtio-devices: Add support for adding a single memory region

Assuming vhost-user devices support CONFIGURE_MEM_SLOTS protocol
feature, we introduce a new method to the VirtioDevice trait in order to
update one single memory at a time.

In case CONFIGURE_MEM_SLOTS is not supported by the backend (feature not
acked), we fallback onto the current way of updating the memory
mappings, that is with SET_MEM_TABLE.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/vhost_user/vu_common_ctrl.rs

@@ -11,7 +11,9 @@ use std::sync::Arc;
 use std::vec::Vec;
 use vhost::vhost_user::{Master, VhostUserMaster};
 use vhost::{VhostBackend, VhostUserMemoryRegionInfo, VringConfigData};
-use vm_memory::{Address, Error as MmapError, GuestMemory, GuestMemoryMmap, GuestMemoryRegion};
+use vm_memory::{
+    Address, Error as MmapError, GuestMemory, GuestMemoryMmap, GuestMemoryRegion, GuestRegionMmap,
+};
 use vmm_sys_util::eventfd::EventFd;
 
 #[derive(Debug, Clone)]
@@ -49,6 +51,24 @@ pub fn update_mem_table(vu: &mut Master, mem: &GuestMemoryMmap) -> Result<()> {
     Ok(())
 }
 
+pub fn add_memory_region(vu: &mut Master, region: &Arc<GuestRegionMmap>) -> Result<()> {
+    let (mmap_handle, mmap_offset) = match region.file_offset() {
+        Some(file_offset) => (file_offset.file().as_raw_fd(), file_offset.start()),
+        None => return Err(Error::MissingRegionFd),
+    };
+
+    let region = VhostUserMemoryRegionInfo {
+        guest_phys_addr: region.start_addr().raw_value(),
+        memory_size: region.len() as u64,
+        userspace_addr: region.as_ptr() as u64,
+        mmap_offset,
+        mmap_handle,
+    };
+
+    vu.add_mem_region(&region)
+        .map_err(Error::VhostUserAddMemReg)
+}
+
 pub fn setup_vhost_user_vring(
     vu: &mut Master,
     mem: &GuestMemoryMmap,