kernel: Start working on a VFS implementation using OOP and SharedPtr

kernel/CMakeLists.txt

@@ -27,6 +27,8 @@ set(SOURCES
     src/sys/clock_gettime.cpp
     src/sys/allocate_memory.cpp
     src/sys/usleep.cpp
+    src/fs/VFS.cpp
+    src/fs/tmpfs/FileSystem.cpp
     src/InitRD.cpp
     src/ELF.cpp
 )

kernel/src/fs/VFS.cpp

@@ -0,0 +1,6 @@
+#include "fs/VFS.h"
+
+namespace VFS
+{
+    SharedPtr<FileSystem> root_fs;
+}

kernel/src/fs/VFS.h

@@ -0,0 +1,37 @@
+#pragma once
+#include <luna/SharedPtr.h>
+
+namespace VFS
+{
+    enum class InodeType
+    {
+        RegularFile,
+        Directory
+    };
+
+    class FileSystem;
+
+    class Inode
+    {
+      public:
+        virtual Result<Inode*> find(const char* name) const = 0;
+
+        virtual FileSystem& fs() const = 0;
+
+        virtual ~Inode() = default;
+
+        InodeType type;
+    };
+
+    class FileSystem
+    {
+      public:
+        virtual Inode& root() const = 0;
+
+        virtual ~FileSystem() = default;
+    };
+
+    extern SharedPtr<FileSystem> root_fs;
+
+    Result<Inode*> resolve_path(const char* path);
+}

kernel/src/fs/tmpfs/FileSystem.cpp

@@ -0,0 +1,33 @@
+#include "fs/tmpfs/FileSystem.h"
+#include <luna/Alloc.h>
+
+namespace TmpFS
+{
+    Result<SharedPtr<VFS::FileSystem>> FileSystem::create()
+    {
+        SharedPtr<Inode> root = TRY(make_shared<Inode>());
+        SharedPtr<FileSystem> fs = TRY(adopt_shared(new (std::nothrow) FileSystem()));
+        root->set_fs(*fs, {});
+        TRY(fs->set_root(root));
+        return (SharedPtr<VFS::FileSystem>)fs;
+    }
+
+    FileSystem::FileSystem()
+    {
+    }
+
+    Result<void> FileSystem::set_root(SharedPtr<VFS::Inode> root)
+    {
+        m_root_inode = root;
+        return m_inodes.try_append(root);
+    }
+
+    Inode::Inode()
+    {
+    }
+
+    void Inode::set_fs(FileSystem& fs, Badge<FileSystem>)
+    {
+        m_fs = &fs;
+    }
+}

kernel/src/fs/tmpfs/FileSystem.h

@@ -0,0 +1,51 @@
+#pragma once
+#include "fs/VFS.h"
+#include <luna/Badge.h>
+#include <luna/Vector.h>
+
+namespace TmpFS
+{
+    class FileSystem : public VFS::FileSystem
+    {
+      public:
+        VFS::Inode& root() const override
+        {
+            return *m_root_inode;
+        }
+
+        static Result<SharedPtr<VFS::FileSystem>> create();
+
+        virtual ~FileSystem() = default;
+
+      private:
+        FileSystem();
+
+        Result<void> set_root(SharedPtr<VFS::Inode> root);
+
+        SharedPtr<VFS::Inode> m_root_inode;
+        Vector<SharedPtr<VFS::Inode>> m_inodes;
+    };
+
+    class Inode : public VFS::Inode
+    {
+      public:
+        Inode();
+
+        void set_fs(FileSystem& fs, Badge<FileSystem>);
+
+        Result<VFS::Inode*> find(const char*) const override
+        {
+            return err(ENOTSUP);
+        }
+
+        VFS::FileSystem& fs() const override
+        {
+            return *m_fs;
+        }
+
+        virtual ~Inode() = default;
+
+      private:
+        VFS::FileSystem* m_fs;
+    };
+}

kernel/src/main.cpp

@@ -7,6 +7,7 @@
 #include "arch/Timer.h"
 #include "boot/Init.h"
 #include "config.h"
+#include "fs/tmpfs/FileSystem.h"
 #include "memory/Heap.h"
 #include "memory/KernelVM.h"
 #include "memory/MemoryManager.h"
@@ -55,6 +56,8 @@ Result<void> init()
     Thread::init();
     Scheduler::init();
 
+    VFS::root_fs = TRY(TmpFS::FileSystem::create());
+
     TarStream::Entry entry;
     while (TRY(g_initrd.read_next_entry(entry)))
     {

luna/include/luna/SharedPtr.h

@@ -117,12 +117,17 @@ template <typename T, class... Args> Result<SharedPtr<T>> make_shared(Args... ar
     return SharedPtr<T> { ptr, ref_count };
 }
 
+// NOTE: ptr is deleted if any of the adopt_shared* functions fail to construct a SharedPtr.
 template <typename T> Result<SharedPtr<T>> adopt_shared(T* ptr)
 {
     using RefCount = __detail::RefCount;
 
+    auto guard = make_scope_guard([ptr] { delete ptr; });
+
     RefCount* const ref_count = TRY(make<RefCount>());
 
+    guard.deactivate();
+
     return SharedPtr<T> { ptr, ref_count };
 }
 
@@ -138,13 +143,7 @@ template <typename T> Result<SharedPtr<T>> adopt_shared_from_owned(OwnedPtr<T>&&
     T* ptr = other.m_ptr;
     other.m_ptr = nullptr;
 
-    // FIXME: Should the pointee magically vanish on failure? Or go back into the OwnedPtr, even though it's been
-    // moved...
-    auto guard = make_scope_guard([&] { delete ptr; });
-
     const SharedPtr<T> shared_ptr = TRY(adopt_shared(ptr));
 
-    guard.deactivate();
-
     return shared_ptr;
 }