feat(tty): 为TTY设备添加page_cache方法并处理无页面缓存的情况 (#1428)

- 在TTY设备中实现page_cache方法，返回None以表明字符设备不需要页面缓存
- 在页面错误处理中增加对无页面缓存情况的处理，避免panic并返回VM_FAULT_SIGBUS

Signed-off-by: longjin <longjin@DragonOS.org>

kernel/src/driver/tty/tty_device.rs

@@ -408,6 +408,11 @@ impl IndexNode for TtyDevice {
         Ok(())
     }
 
+    fn page_cache(&self) -> Option<Arc<crate::filesystem::page_cache::PageCache>> {
+        // TTY设备是字符设备，不需要页面缓存
+        None
+    }
+
     fn close(&self, data: SpinLockGuard<FilePrivateData>) -> Result<(), SystemError> {
         let (tty, _flags) = if let FilePrivateData::Tty(tty_priv) = &*data {
             (tty_priv.tty(), tty_priv.flags)

kernel/src/mm/fault.rs

@@ -609,7 +609,17 @@ impl PageFaultHandler {
         let vma = pfm.vma();
         let vma_guard = vma.lock_irqsave();
         let file = vma_guard.vm_file().expect("no vm_file in vma");
-        let page_cache = file.inode().page_cache().unwrap();
+        let page_cache = match file.inode().page_cache() {
+            Some(cache) => cache,
+            None => {
+                // 文件没有页面缓存，可能是不支持内存映射的设备文件
+                log::warn!(
+                    "filemap_map_pages: file has no page cache, inode type: {}",
+                    crate::libs::name::get_type_name(&file.inode())
+                );
+                return VmFaultReason::VM_FAULT_SIGBUS;
+            }
+        };
         let mapper = &mut pfm.mapper;
 
         // 起始页地址
@@ -650,7 +660,17 @@ impl PageFaultHandler {
         let vma = pfm.vma();
         let vma_guard = vma.lock_irqsave();
         let file = vma_guard.vm_file().expect("no vm_file in vma");
-        let page_cache = file.inode().page_cache().unwrap();
+        let page_cache = match file.inode().page_cache() {
+            Some(cache) => cache,
+            None => {
+                // 文件没有页面缓存，可能是不支持内存映射的设备文件
+                log::warn!(
+                    "filemap_fault: file has no page cache, inode type: {}",
+                    crate::libs::name::get_type_name(&file.inode())
+                );
+                return VmFaultReason::VM_FAULT_SIGBUS;
+            }
+        };
         let file_pgoff = pfm.file_pgoff.expect("no file_pgoff");
         let mut ret = VmFaultReason::empty();