kernel/vfs: prepare fs type registration support

5 files changed, 98 insertions, 0 deletions

diff --git a/arch/x86_64/scripts/kernel.ld b/arch/x86_64/scripts/kernel.ld
index a429570..388c46e 100644
--- a/arch/x86_64/scripts/kernel.ld
+++ b/arch/x86_64/scripts/kernel.ld
@@ -72,6 +72,11 @@ SECTIONS
   .kernel_rodata ALIGN(4K) : AT (ADDR (.kernel_rodata) - TEACHOS_VMA)
   {
     *(.rodata*)
+
+    . = ALIGN(8);
+    PROVIDE(__vfs_type_descriptors_begin = .);
+    KEEP(*(.vfs_type_descriptors*));
+    PROVIDE(__vfs_type_descriptors_end = .);
   } :kernel_rodata
 
   .kernel_data ALIGN(4K) : AT (ADDR (.kernel_data) - TEACHOS_VMA)
diff --git a/kernel/include/kernel/filesystem/type.hpp b/kernel/include/kernel/filesystem/type.hpp
new file mode 100644
index 0000000..87e466b
--- /dev/null
+++ b/kernel/include/kernel/filesystem/type.hpp
@@ -0,0 +1,33 @@
+#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;
+  };
+
+}  // namespace kernel::filesystem
+
+#endif
diff --git a/kernel/src/filesystem/devfs/filesystem.cpp b/kernel/src/filesystem/devfs/filesystem.cpp
index f0d8bf7..c61a3d0 100644
--- a/kernel/src/filesystem/devfs/filesystem.cpp
+++ b/kernel/src/filesystem/devfs/filesystem.cpp
@@ -5,6 +5,7 @@
 #include <kernel/filesystem/devfs/inode.hpp>
 #include <kernel/filesystem/device_inode.hpp>
 #include <kernel/filesystem/inode.hpp>
+#include <kernel/filesystem/type.hpp>
 
 #include <kapi/devices/device.hpp>
 
@@ -15,6 +16,27 @@
 
 namespace kernel::filesystem::devfs
 {
+  struct type final : kernel::filesystem::type
+  {
+    [[nodiscard]] auto name() const noexcept -> std::string_view override
+    {
+      return "devfs";
+    }
+
+    [[nodiscard]] auto requires_device() const noexcept -> bool override
+    {
+      return false;
+    }
+
+    [[nodiscard]] auto make_instance() const -> kstd::shared_ptr<kernel::filesystem::filesystem> override
+    {
+      return kstd::make_shared<filesystem>();
+    }
+  } const constinit type_instance{};
+
+  [[gnu::section(".vfs_type_descriptors"), gnu::used]]
+  auto const * const type_descriptor_pointer = static_cast<kernel::filesystem::type const *>(&type_instance);
+
   auto filesystem::mount(kstd::shared_ptr<kernel::filesystem::inode> const &) -> operation_result
   {
     m_root_inode = kstd::make_shared<inode>();
diff --git a/kernel/src/filesystem/ext2/filesystem.cpp b/kernel/src/filesystem/ext2/filesystem.cpp
index 12aeaaa..6959653 100644
--- a/kernel/src/filesystem/ext2/filesystem.cpp
+++ b/kernel/src/filesystem/ext2/filesystem.cpp
@@ -6,6 +6,7 @@
 #include <kernel/filesystem/ext2/superblock.hpp>
 #include <kernel/filesystem/filesystem.hpp>
 #include <kernel/filesystem/inode.hpp>
+#include <kernel/filesystem/type.hpp>
 
 #include <kstd/memory>
 #include <kstd/unikstd.h>
@@ -18,6 +19,28 @@
 
 namespace kernel::filesystem::ext2
 {
+
+  struct type final : kernel::filesystem::type
+  {
+    [[nodiscard]] auto name() const noexcept -> std::string_view override
+    {
+      return "ext2";
+    }
+
+    [[nodiscard]] auto requires_device() const noexcept -> bool override
+    {
+      return true;
+    }
+
+    [[nodiscard]] auto make_instance() const -> kstd::shared_ptr<kernel::filesystem::filesystem> override
+    {
+      return kstd::make_shared<filesystem>();
+    }
+  } const constinit type_instance{};
+
+  [[gnu::section(".vfs_type_descriptors"), gnu::used]]
+  auto const * const type_descriptor_pointer = static_cast<kernel::filesystem::type const *>(&type_instance);
+
   auto filesystem::mount(kstd::shared_ptr<kernel::filesystem::inode> const & backing_inode) -> operation_result
   {
     kernel::filesystem::filesystem::mount(backing_inode);
diff --git a/kernel/src/filesystem/vfs.cpp b/kernel/src/filesystem/vfs.cpp
index ae85291..d22c74b 100644
--- a/kernel/src/filesystem/vfs.cpp
+++ b/kernel/src/filesystem/vfs.cpp
@@ -8,10 +8,12 @@
 #include <kernel/filesystem/mount_table.hpp>
 #include <kernel/filesystem/path.hpp>
 #include <kernel/filesystem/rootfs/filesystem.hpp>
+#include <kernel/filesystem/type.hpp>
 
 #include <kapi/system.hpp>
 
 #include <kstd/memory>
+#include <kstd/print>
 #include <kstd/string>
 #include <kstd/vector>
 
@@ -19,9 +21,16 @@
 #include <cstdint>
 #include <optional>
 #include <ranges>
+#include <span>
 #include <string_view>
 #include <utility>
 
+extern "C"
+{
+  extern kernel::filesystem::type const * const __vfs_type_descriptors_begin;
+  extern kernel::filesystem::type const * const __vfs_type_descriptors_end;
+}
+
 namespace
 {
   constinit auto static active_vfs = std::optional<kernel::filesystem::vfs>{};
@@ -42,6 +51,12 @@ namespace kernel::filesystem
 
   auto vfs::init_internal() -> void
   {
+    auto type_descriptors = std::span{&__vfs_type_descriptors_begin, &__vfs_type_descriptors_end} |
+                            std::views::filter([](auto p) { return p != nullptr; });
+    std::ranges::for_each(type_descriptors, [](auto descriptor) {
+      kstd::println("[OS] registering filesystem '{}'", descriptor->name());
+    });
+
     // mount rootfs at /
     auto root_fs = kstd::make_shared<rootfs::filesystem>();
     root_fs->mount(nullptr);