Merge branch 'fmorgner/develop-BA-FS26/dynamic-fs' into 'develop-BA-FS26'

Add support infrastructure for automatic file system registration

See merge request teachos/kernel!46

3 files changed, 98 insertions, 4 deletions

diff --git a/kernel/include/kernel/filesystem/type.hpp b/kernel/include/kernel/filesystem/type.hpp
new file mode 100644
index 0000000..0948e54
--- /dev/null
+++ b/kernel/include/kernel/filesystem/type.hpp
@@ -0,0 +1,42 @@
+#ifndef TEACH_OS_KERNEL_FILESYSTEM_TYPE_HPP
+#define TEACH_OS_KERNEL_FILESYSTEM_TYPE_HPP
+
+#include <kernel/filesystem/filesystem.hpp>
+
+#include <kstd/memory>
+
+#include <string_view>
+
+namespace kernel::filesystem
+{
+
+  //! A type descriptor for a filesystem driver.
+  //!
+  //! Each filesystem must expose an instance of a class derived from this type in order to be registered with the vfs
+  //! filesystem registry.
+  struct type
+  {
+    virtual ~type() = default;
+
+    //! Get the name of the filesystem represented by this descriptor.
+    [[nodiscard]] virtual auto name() const noexcept -> std::string_view = 0;
+
+    //! Check if filesystems of this type require a device to back them.
+    [[nodiscard]] virtual auto requires_device() const noexcept -> bool = 0;
+
+    //! Create a new instance of the filesytem represented by this descriptor.
+    [[nodiscard]] virtual auto make_instance() const -> kstd::shared_ptr<filesystem> = 0;
+  };
+
+  template<typename Type>
+  struct type_registration
+  {
+    constexpr auto static instance = Type{};
+    [[using gnu: section("fs_types"), used, visibility("hidden")]] constexpr auto static pointer{
+      kstd::make_observer<type const>(&instance),
+    };
+  };
+
+}  // namespace kernel::filesystem
+
+#endif
diff --git a/kernel/include/kernel/filesystem/type_registry.hpp b/kernel/include/kernel/filesystem/type_registry.hpp
new file mode 100644
index 0000000..3be7295
--- /dev/null
+++ b/kernel/include/kernel/filesystem/type_registry.hpp
@@ -0,0 +1,53 @@
+#ifndef TEACH_OS_KERNEL_TYPE_REGISRY_HPP
+#define TEACH_OS_KERNEL_TYPE_REGISRY_HPP
+
+#include <kernel/filesystem/type.hpp>
+
+#include <kstd/flat_map>
+#include <kstd/memory>
+#include <kstd/string>
+
+#include <cstddef>
+#include <span>
+#include <string_view>
+
+namespace kernel::filesystem
+{
+
+  struct type_registry
+  {
+    using value_type = type;
+    using pointer = kstd::observer_ptr<value_type const>;
+
+    auto static init() -> void;
+    auto static get() -> type_registry &;
+
+    constexpr type_registry() noexcept = default;
+
+    //! Add a type descriptor to this registry.
+    //!
+    //! This function will register the given descriptor with this registry, given that no descriptor for a filesystem
+    //! with the same name exists in this registry already.
+    //!
+    //! @param descriptor The filesystem type descriptor to add to the registry.
+    //! @return @p true iff. the descriptor was successfully added, @p false if not.
+    auto add(pointer descriptor) -> bool;
+
+    //! Get all currently registered type descriptors.
+    //!
+    //! @return A span containing all currently registered filesystem type descriptors.
+    [[nodiscard]] auto all() const noexcept -> std::span<pointer const>;
+
+    //! Get the number of registered filesystem types.
+    //!
+    //! @return The number of filesystem descriptors currently registered with this registry.
+    [[nodiscard]] auto size() const noexcept -> std::size_t;
+
+  private:
+    //! A map from filesystem names (identifiers) to filesystem type descriptors.
+    kstd::flat_map<std::string_view, pointer> m_descriptors{};
+  };
+
+}  // namespace kernel::filesystem
+
+#endif
diff --git a/kernel/include/kernel/filesystem/vfs.hpp b/kernel/include/kernel/filesystem/vfs.hpp
index e6f2327..ddc9a9b 100644
--- a/kernel/include/kernel/filesystem/vfs.hpp
+++ b/kernel/include/kernel/filesystem/vfs.hpp
@@ -35,6 +35,8 @@ namespace kernel::filesystem
       invalid_filesystem = -5
     };
 
+    vfs();
+
     /**
     @brief Initialize the virtual filesystem.
     @warning Panics if the VFS has already been initialized.
@@ -83,9 +85,6 @@ namespace kernel::filesystem
     auto unmount(std::string_view path) -> operation_result;
 
   private:
-    vfs() = default;
-    auto init_internal() -> void;
-
     /**
      * Note: Resolving a dentry requires traversing mount points; since the
      * associated 'mount' object is discovered as a byproduct of this
@@ -107,7 +106,7 @@ namespace kernel::filesystem
 
     auto graft_persistent_device_fs(kstd::shared_ptr<devfs::filesystem> const & device_fs) -> void;
 
-    mount_table m_mount_table;
+    mount_table m_mount_table{};
   };
 }  // namespace kernel::filesystem