From 493f50c697b17049b820e65664af9f4a7c9c0c2c Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Tue, 18 Aug 2026 00:25:29 +0200
Subject: kapi: implement seek support

---
 kapi/kapi/filesystem.hpp                          |  8 ++--
 kapi/kapi/filesystem/seek.hpp                     | 30 +++++++++++++++
 kapi/kapi/filesystem/seek_origin.hpp              | 22 -----------
 kernel/kapi/filesystem.cpp                        |  8 ++++
 kernel/kapi/filesystem.tests.cpp                  | 19 ++++++++++
 kernel/kernel/filesystem/open_file_descriptor.cpp | 46 +++++++++++++++++++++++
 kernel/kernel/filesystem/open_file_descriptor.hpp | 11 ++++++
 7 files changed, 119 insertions(+), 25 deletions(-)
 create mode 100644 kapi/kapi/filesystem/seek.hpp
 delete mode 100644 kapi/kapi/filesystem/seek_origin.hpp

diff --git a/kapi/kapi/filesystem.hpp b/kapi/kapi/filesystem.hpp
index 8972f9d3..be754748 100644
--- a/kapi/kapi/filesystem.hpp
+++ b/kapi/kapi/filesystem.hpp
@@ -7,7 +7,7 @@
 #include <kapi/filesystem/device_number.hpp>           // IWYU pragma: export
 #include <kapi/filesystem/file_status.hpp>             // IWYU pragma: export
 #include <kapi/filesystem/file_type.hpp>               // IWYU pragma: export
-#include <kapi/filesystem/seek_origin.hpp>             // IWYU pragma: export
+#include <kapi/filesystem/seek.hpp>                    // IWYU pragma: export
 
 #include <kstd/result.hpp>
 #include <kstd/system_error.hpp>
@@ -70,10 +70,12 @@ namespace kapi::filesystem
   //! Adjust the current position in the file.
   //!
   //! @param file_descriptor The file descriptor to seek.
-  //! @param offset The offset to seek to, relative to @p origin.
+  //! @param offset The offset to seek to, relative to the origin.
+  //! @param direction The direction to seek towards, relative to the origin.
   //! @param origin The origing to seek relatively to.
   //! @return The new position in the file on success, an error code otherwise.
-  auto seek(size_t file_descriptor, kstd::units::bytes offset, seek_origin origin) -> kstd::result<kstd::units::bytes>;
+  auto seek(size_t file_descriptor, kstd::units::bytes offset, seek_direction direction, seek_origin origin)
+      -> kstd::result<kstd::units::bytes>;
 
   //! Create a new directory at the specified path.
   //!
diff --git a/kapi/kapi/filesystem/seek.hpp b/kapi/kapi/filesystem/seek.hpp
new file mode 100644
index 00000000..f1006f31
--- /dev/null
+++ b/kapi/kapi/filesystem/seek.hpp
@@ -0,0 +1,30 @@
+#ifndef TEACHOS_KAPI_FILESYSTEM_SEEK_HPP
+#define TEACHOS_KAPI_FILESYSTEM_SEEK_HPP
+
+// IWYU pragma: private, include <kapi/filesystem.hpp>
+
+namespace kapi::filesystem
+{
+
+  //! The origin for a seek operation.
+  enum struct seek_origin
+  {
+    //! Seek from the beginning of the file.
+    beginning,
+    //! Seek from the current position.
+    current_position,
+    //! Seek from the end of the file.
+    end,
+  };
+
+  enum struct seek_direction
+  {
+    //! seek forward from the origin.
+    forward,
+    //! seek backward from the origin.
+    backward,
+  };
+
+}  // namespace kapi::filesystem
+
+#endif
\ No newline at end of file
diff --git a/kapi/kapi/filesystem/seek_origin.hpp b/kapi/kapi/filesystem/seek_origin.hpp
deleted file mode 100644
index 4307f451..00000000
--- a/kapi/kapi/filesystem/seek_origin.hpp
+++ /dev/null
@@ -1,22 +0,0 @@
-#ifndef TEACHOS_KAPI_FILESYSTEM_SEEK_ORIGIN_HPP
-#define TEACHOS_KAPI_FILESYSTEM_SEEK_ORIGIN_HPP
-
-// IWYU pragma: private, include <kapi/filesystem.hpp>
-
-namespace kapi::filesystem
-{
-
-  //! The origin for a seek operation.
-  enum class seek_origin
-  {
-    //! Seek from the beginning of the file.
-    beginning,
-    //! Seek from the current position.
-    current_position,
-    //! Seek from the end of the file.
-    end,
-  };
-
-}  // namespace kapi::filesystem
-
-#endif
\ No newline at end of file
diff --git a/kernel/kapi/filesystem.cpp b/kernel/kapi/filesystem.cpp
index 5280b4fa..d37a4cf7 100644
--- a/kernel/kapi/filesystem.cpp
+++ b/kernel/kapi/filesystem.cpp
@@ -57,6 +57,14 @@ namespace kapi::filesystem
     });
   }
 
+  auto seek(size_t file_descriptor, kstd::units::bytes offset, seek_direction direction, seek_origin origin)
+      -> kstd::result<kstd::units::bytes>
+  {
+    return kernel::filesystem::open_file_table::get().file(file_descriptor).and_then([=](auto file) {
+      return file->seek(offset, direction, origin);
+    });
+  }
+
   auto mkdir(std::string_view path) -> kstd::result<void>
   {
     return kernel::filesystem::vfs::get().mkdir(path);
diff --git a/kernel/kapi/filesystem.tests.cpp b/kernel/kapi/filesystem.tests.cpp
index 80fc7d3f..2f975bf8 100644
--- a/kernel/kapi/filesystem.tests.cpp
+++ b/kernel/kapi/filesystem.tests.cpp
@@ -3,6 +3,7 @@
 #include <kernel/test_support/filesystem/storage_boot_module_vfs_fixture.hpp>
 
 #include <kstd/system_error.hpp>
+#include <kstd/units.hpp>
 
 #include <catch2/catch_test_macros.hpp>
 
@@ -142,6 +143,24 @@ SCENARIO_METHOD(kernel::tests::filesystem::storage_boot_module_vfs_fixture, "Kap
       REQUIRE(kapi::filesystem::umount("/information"));
     }
 
+    AND_GIVEN("an open file")
+    {
+      auto file = kapi::filesystem::open("/closed.txt");
+      REQUIRE(file);
+
+      THEN("seeking forward from the beginning succeeds")
+      {
+        REQUIRE(kapi::filesystem::seek(*file, 100_B, kapi::filesystem::seek_direction::forward,
+                                       kapi::filesystem::seek_origin::beginning) == 100_B);
+      }
+
+      THEN("seeking backward from the beginning fails")
+      {
+        REQUIRE_FALSE(kapi::filesystem::seek(*file, 100_B, kapi::filesystem::seek_direction::backward,
+                                             kapi::filesystem::seek_origin::beginning));
+      }
+    }
+
     THEN("device can be opened as file and read from")
     {
       auto fd = kapi::filesystem::open("/dev/ram0").value();
diff --git a/kernel/kernel/filesystem/open_file_descriptor.cpp b/kernel/kernel/filesystem/open_file_descriptor.cpp
index 71dd172b..379b0708 100644
--- a/kernel/kernel/filesystem/open_file_descriptor.cpp
+++ b/kernel/kernel/filesystem/open_file_descriptor.cpp
@@ -1,6 +1,9 @@
 #include <kernel/filesystem/open_file_descriptor.hpp>
 
 #include <kernel/filesystem/dentry.hpp>
+#include <kernel/filesystem/error.hpp>
+
+#include <kapi/filesystem.hpp>
 
 #include <kstd/memory.hpp>
 #include <kstd/os/error.hpp>
@@ -50,6 +53,49 @@ namespace kernel::filesystem
     }
   }
 
+  auto open_file_descriptor::seek(kstd::units::bytes offset, kapi::filesystem::seek_direction direction,
+                                  kapi::filesystem::seek_origin origin) -> kstd::result<kstd::units::bytes>
+  {
+    switch (origin)
+    {
+      case kapi::filesystem::seek_origin::beginning:
+      {
+        if (direction == kapi::filesystem::seek_direction::backward)
+        {
+          return kstd::failure(vfs_errc::invalid_argument);
+        }
+        return m_offset = offset;
+      }
+      case kapi::filesystem::seek_origin::current_position:
+      {
+        if (direction == kapi::filesystem::seek_direction::backward)
+        {
+          if (offset > m_offset)
+          {
+            return kstd::failure(vfs_errc::invalid_argument);
+          }
+          return m_offset -= offset;
+        }
+        return m_offset += offset;
+      }
+      case kapi::filesystem::seek_origin::end:
+      {
+        auto base = m_dentry->get_inode()->status()->size;
+        if (direction == kapi::filesystem::seek_direction::backward)
+        {
+          if (offset > base)
+          {
+            return kstd::failure(vfs_errc::invalid_argument);
+          }
+          return m_offset = base - offset;
+        }
+        return m_offset = base + offset;
+      }
+    }
+
+    return kstd::failure(vfs_errc::invalid_argument);
+  }
+
   auto open_file_descriptor::offset() const -> kstd::units::bytes
   {
     return m_offset;
diff --git a/kernel/kernel/filesystem/open_file_descriptor.hpp b/kernel/kernel/filesystem/open_file_descriptor.hpp
index 247108c1..f0b55d72 100644
--- a/kernel/kernel/filesystem/open_file_descriptor.hpp
+++ b/kernel/kernel/filesystem/open_file_descriptor.hpp
@@ -3,6 +3,8 @@
 
 #include <kernel/filesystem/dentry.hpp>
 
+#include <kapi/filesystem.hpp>
+
 #include <kstd/memory.hpp>
 #include <kstd/result.hpp>
 #include <kstd/units.hpp>
@@ -47,6 +49,15 @@ namespace kernel::filesystem
     */
     auto write(std::span<std::byte const> buffer) -> kstd::result<kstd::units::bytes>;
 
+    //! Move the read/write offset of the file.
+    //!
+    //! @param offset The offset to apply relative to the given origin.
+    //! @param offset The direction to seek in, relative to the given origin.
+    //! @param origin The origin of the offset.
+    //! @return the new offset on success, an error otherwise.
+    auto seek(kstd::units::bytes offset, kapi::filesystem::seek_direction direction,
+              kapi::filesystem::seek_origin origin) -> kstd::result<kstd::units::bytes>;
+
     /**
     @brief Returns the current file offset for this open file descriptor.
     @return The current file offset in bytes.
-- 
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