From cefeea7b50427da70cf802c84fdf0cd92e283264 Mon Sep 17 00:00:00 2001
From: Ruihan Li <lrh2000@pku.edu.cn>
Date: Sat, 24 Aug 2024 12:56:08 +0800
Subject: [PATCH] Revise `IoMem::resize` into `IoMem::slice`

---
 .../comps/virtio/src/transport/mmio/device.rs |  5 +--
 .../comps/virtio/src/transport/pci/device.rs  | 17 +++------
 ostd/src/io_mem.rs                            | 35 +++++++------------
 3 files changed, 19 insertions(+), 38 deletions(-)

diff --git a/kernel/comps/virtio/src/transport/mmio/device.rs b/kernel/comps/virtio/src/transport/mmio/device.rs
index a9db5b07a..97584537b 100644
--- a/kernel/comps/virtio/src/transport/mmio/device.rs
+++ b/kernel/comps/virtio/src/transport/mmio/device.rs
@@ -198,10 +198,7 @@ impl VirtioTransport for VirtioMmioTransport {
 
     fn device_config_memory(&self) -> IoMem {
         // offset: 0x100~0x200
-        let mut io_mem = self.common_device.io_mem().clone();
-        let paddr = io_mem.paddr();
-        io_mem.resize((paddr + 0x100)..(paddr + 0x200)).unwrap();
-        io_mem
+        self.common_device.io_mem().slice(0x100..0x200)
     }
 
     fn device_features(&self) -> u64 {
diff --git a/kernel/comps/virtio/src/transport/pci/device.rs b/kernel/comps/virtio/src/transport/pci/device.rs
index 6d90e09ad..02f0c0066 100644
--- a/kernel/comps/virtio/src/transport/pci/device.rs
+++ b/kernel/comps/virtio/src/transport/pci/device.rs
@@ -125,18 +125,11 @@ impl VirtioTransport for VirtioPciTransport {
     }
 
     fn device_config_memory(&self) -> IoMem {
-        let mut memory = self
-            .device_cfg
-            .memory_bar()
-            .as_ref()
-            .unwrap()
-            .io_mem()
-            .clone();
-        let new_paddr = memory.paddr() + self.device_cfg.offset() as usize;
-        memory
-            .resize(new_paddr..(self.device_cfg.length() as usize + new_paddr))
-            .unwrap();
-        memory
+        let memory = self.device_cfg.memory_bar().as_ref().unwrap().io_mem();
+
+        let offset = self.device_cfg.offset() as usize;
+        let length = self.device_cfg.length() as usize;
+        memory.slice(offset..offset + length)
     }
 
     fn device_features(&self) -> u64 {
diff --git a/ostd/src/io_mem.rs b/ostd/src/io_mem.rs
index 1e2f58c6e..a0a6597f3 100644
--- a/ostd/src/io_mem.rs
+++ b/ostd/src/io_mem.rs
@@ -34,8 +34,8 @@ impl IoMem {
     /// - The given physical address range must be in the I/O memory region.
     /// - Reading from or writing to I/O memory regions may have side effects. Those side effects
     ///   must not cause soundness problems (e.g., they must not corrupt the kernel memory).
-    pub(crate) unsafe fn new(range: Range<Paddr>) -> IoMem {
-        IoMem {
+    pub(crate) unsafe fn new(range: Range<Paddr>) -> Self {
+        Self {
             virtual_address: paddr_to_vaddr(range.start),
             limit: range.len(),
         }
@@ -51,29 +51,20 @@ impl IoMem {
         self.limit
     }
 
-    /// Resizes the I/O memory region to the new `range`.
+    /// Slices the `IoMem`, returning another `IoMem` representing the subslice.
     ///
-    /// # Errors
+    /// # Panics
     ///
-    /// Returns an error if the new `range` is not within the current range.
-    pub fn resize(&mut self, range: Range<Paddr>) -> Result<()> {
-        let start_vaddr = paddr_to_vaddr(range.start);
-        let virtual_end = self
-            .virtual_address
-            .checked_add(self.limit)
-            .ok_or(Error::Overflow)?;
-        if start_vaddr < self.virtual_address || start_vaddr >= virtual_end {
-            return Err(Error::InvalidArgs);
+    /// This method will panic if the range is empty or out of bounds.
+    pub fn slice(&self, range: Range<usize>) -> Self {
+        // This ensures `range.start < range.end` and `range.end <= limit`.
+        assert!(!range.is_empty() && range.end <= self.limit);
+
+        // We've checked the range is in bounds, so we can construct the new `IoMem` safely.
+        Self {
+            virtual_address: self.virtual_address + range.start,
+            limit: range.end - range.start,
         }
-        let end_vaddr = start_vaddr
-            .checked_add(range.len())
-            .ok_or(Error::Overflow)?;
-        if end_vaddr <= self.virtual_address || end_vaddr > virtual_end {
-            return Err(Error::InvalidArgs);
-        }
-        self.virtual_address = start_vaddr;
-        self.limit = range.len();
-        Ok(())
     }
 }