virtio-devices: Port devices over to new read_config_from_slice() helper

Using this helper removes lots of duplicated code across the devices.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

virtio-devices/src/pmem.rs

@@ -15,10 +15,9 @@ use crate::{VirtioInterrupt, VirtioInterruptType};
 use anyhow::anyhow;
 use libc::EFD_NONBLOCK;
 use serde::ser::{Serialize, SerializeStruct, Serializer};
-use std::cmp;
 use std::fmt::{self, Display};
 use std::fs::File;
-use std::io::{self, Write};
+use std::io;
 use std::mem::size_of;
 use std::os::unix::io::{AsRawFd, FromRawFd};
 use std::result;
@@ -463,19 +462,8 @@ impl VirtioDevice for Pmem {
         self.acked_features |= v;
     }
 
-    fn read_config(&self, offset: u64, mut data: &mut [u8]) {
-        let config_slice = self.config.as_slice();
-        let config_len = config_slice.len() as u64;
-        if offset >= config_len {
-            error!("Failed to read config space");
-            return;
-        }
-
-        if let Some(end) = offset.checked_add(data.len() as u64) {
-            // This write can't fail, offset and end are checked against config_len.
-            data.write_all(&config_slice[offset as usize..cmp::min(end, config_len) as usize])
-                .unwrap();
-        }
+    fn read_config(&self, offset: u64, data: &mut [u8]) {
+        self.read_config_from_slice(self.config.as_slice(), offset, data);
     }
 
     fn activate(