From 26a34c3eae661235b8cfeb79ffc977f8379b57c4 Mon Sep 17 00:00:00 2001
From: Bruce Leidl <bruce@subgraph.com>
Date: Wed, 11 Sep 2019 11:29:24 -0400
Subject: [PATCH] A class which manages virtio device config area

---
 rust/src/virtio/device_config.rs | 97 ++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 rust/src/virtio/device_config.rs

diff --git a/rust/src/virtio/device_config.rs b/rust/src/virtio/device_config.rs
new file mode 100644
index 0000000..d2975fa
--- /dev/null
+++ b/rust/src/virtio/device_config.rs
@@ -0,0 +1,97 @@
+
+use byteorder::{ByteOrder,LittleEndian};
+use std::ops::Range;
+
+pub struct DeviceConfigArea {
+    buffer: Vec<u8>,
+    write_filter: DeviceConfigWriteFilter,
+}
+
+
+impl DeviceConfigArea {
+    pub fn new(size: usize) -> Self {
+        DeviceConfigArea{
+            buffer: vec![0u8; size],
+            write_filter: DeviceConfigWriteFilter::new(size),
+        }
+    }
+
+    pub fn read_config(&self, offset: usize, size: usize) -> u64 {
+        if offset + size > self.buffer.len() {
+            return 0;
+        }
+        match size {
+            1 => self.buffer[offset] as u64,
+            2 => LittleEndian::read_u16(&self.buffer[offset..]) as u64,
+            4 => LittleEndian::read_u32(&self.buffer[offset..]) as u64,
+            8 => LittleEndian::read_u64(&self.buffer[offset..]),
+            _ => 0,
+        }
+    }
+
+    pub fn write_config(&mut self, offset: usize, size: usize, val: u64) {
+        if self.write_filter.is_writeable(offset, size) {
+            match size {
+                1 => self.write_u8(offset, val as u8),
+                2 => self.write_u16(offset, val as u16),
+                4 => self.write_u32(offset, val as u32),
+                8 => self.write_u64(offset, val as u64),
+                _ => {},
+            }
+        }
+    }
+
+    pub fn set_writeable(&mut self, offset: usize, size: usize) {
+        self.write_filter.set_writable(offset, size)
+    }
+
+    pub fn write_u8(&mut self, offset: usize, val: u8) {
+        assert!(offset + 1 <= self.buffer.len());
+        self.buffer[offset] = val;
+    }
+
+    pub fn write_u16(&mut self, offset: usize, val: u16) {
+        assert!(offset + 2 <= self.buffer.len());
+        LittleEndian::write_u16(&mut self.buffer[offset..], val);
+    }
+
+    pub fn write_u32(&mut self, offset: usize, val: u32) {
+        assert!(offset + 4 <= self.buffer.len());
+        LittleEndian::write_u32(&mut self.buffer[offset..], val);
+    }
+
+    pub fn write_u64(&mut self, offset: usize, val: u64) {
+        assert!(offset + 8 <= self.buffer.len());
+        LittleEndian::write_u64(&mut self.buffer[offset..], val);
+    }
+
+    pub fn write_bytes(&mut self, offset: usize, bytes: &[u8]) {
+        assert!(offset + bytes.len() <= self.buffer.len());
+        self.buffer[offset..offset + bytes.len()].copy_from_slice(bytes);
+    }
+}
+
+struct DeviceConfigWriteFilter {
+    size: usize,
+    ranges: Vec<Range<usize>>,
+}
+
+impl DeviceConfigWriteFilter {
+    fn new(size: usize) -> Self {
+        DeviceConfigWriteFilter { size, ranges: Vec::new() }
+    }
+
+    fn set_writable(&mut self, offset: usize, size: usize) {
+        let end = offset + size;
+        self.ranges.push(offset..end);
+    }
+
+    fn is_writeable(&self, offset: usize, size: usize) -> bool {
+        if offset + size > self.size {
+            false
+        } else {
+            let last = offset + size - 1;
+            self.ranges.iter().any(|r| r.contains(&offset) && r.contains(&last))
+        }
+    }
+}
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