From 15e62510104bc0e2b9180b66e5845d985cac03cc Mon Sep 17 00:00:00 2001
From: Benji Dial <benji@benjidial.net>
Date: Wed, 10 Jan 2024 00:17:29 -0500
Subject: partial (largely untested) memory block device and tar file system
 support

---
 include/mercury/kernel/storage.hpp | 130 +++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 include/mercury/kernel/storage.hpp

(limited to 'include/mercury/kernel/storage.hpp')

diff --git a/include/mercury/kernel/storage.hpp b/include/mercury/kernel/storage.hpp
new file mode 100644
index 0000000..1374766
--- /dev/null
+++ b/include/mercury/kernel/storage.hpp
@@ -0,0 +1,130 @@
+#ifndef MERCURY_KERNEL_STORAGE_HPP
+#define MERCURY_KERNEL_STORAGE_HPP
+
+#include <mercury/kernel/utility.hpp>
+#include <cstdint>
+
+namespace mercury::kernel::storage {
+
+  typedef uint64_t node_id_t;
+  typedef uint64_t directory_iter_t;
+
+  enum file_type {
+    regular_file,
+    directory,
+    symlink
+  };
+
+  enum io_result {
+    success,
+    mount_point_already_used,
+    not_a_directory,
+    not_supported,
+    out_of_bounds,
+    device_error,
+    fs_corrupt,
+    not_found,
+    bad_path,
+  };
+
+  class file_system_instance {
+
+  public:
+    virtual ~file_system_instance() {}
+
+    virtual io_result get_root_node(node_id_t &out) = 0;
+
+    //get_first_child sets iter_out to a "directory iterator" representing the
+    //first child of this node. get_next_child gets the child after the child
+    //represented by the value of iter passed in, and changes iter to represent
+    //that next child. for an empty directory node, get_first_child returns
+    //io_result::out_of_bounds. when iter represents the last child of a node,
+    //get_next_child also returns io_result::out_of_bounds.
+    virtual io_result get_first_child(node_id_t node, node_id_t &out, directory_iter_t &iter_out) = 0;
+    virtual io_result get_next_child(node_id_t node, node_id_t &out, directory_iter_t &iter) = 0;
+    virtual io_result get_child(node_id_t node, node_id_t &out, const char *name, size_t name_len) = 0;
+
+    virtual io_result get_name_length(node_id_t node, size_t &length_out) = 0;
+    //buffer is assumed to be long enough - call get_name_length first.
+    virtual io_result get_name(node_id_t node, char *buffer, size_t &length_out) = 0;
+
+    virtual io_result get_file_length(node_id_t node, uint64_t &length_out) = 0;
+
+    virtual io_result get_file_type(node_id_t node, file_type &out) = 0;
+  };
+
+  class block_device {
+
+  private:
+    uint8_t *block_cache;
+    uint64_t block_cache_i;
+    bool block_cache_dirty;
+
+    io_result load_cache_block(uint64_t i);
+
+  protected:
+    //implemented in driver, bounds not checked
+    virtual io_result read_blocks_no_cache(uint64_t start, uint64_t count, void *into) = 0;
+    virtual io_result write_blocks_no_cache(uint64_t start, uint64_t count, const void *from) = 0;
+
+    //it is assumed that this is only called once, by the driver, after
+    //block_size and block_count have been set, and before read_bytes or
+    //write_bytes can be called (e.g. in the derived class's constructor)
+    void allocate_block_cache();
+
+  public:
+    //set by storage component
+    file_system_instance *mounted_as;
+    utility::uuid id;
+
+    //set by driver
+    uint64_t block_size;
+    uint64_t block_count;
+
+    virtual ~block_device() {
+      if (block_cache)
+        delete block_cache;
+    }
+
+    io_result read_bytes(uint64_t start, uint64_t count, void *into);
+    io_result write_bytes(uint64_t start, uint64_t count, const void *from);
+
+  };
+
+  typedef io_result (*file_system_mounter)(block_device *bd, file_system_instance *&fs_out);
+
+  extern utility::list<block_device *> *block_devices;
+
+  void init_storage();
+
+  //a canon path contains no . or empty directory names, and
+  //contains no .. except for at the start of a relative path.
+  struct canon_path {
+
+    bool absolute;
+    unsigned parent_count;
+    utility::vector<utility::string> segments;
+
+    void parent();
+    void rel(const canon_path &r);
+
+    utility::string to_string(bool trailing_slash) const;
+
+  };
+
+  void canonize_path(const char *str, size_t len, canon_path &out);
+
+  //path must be absolute.
+  io_result mount_device(block_device *bd, const canon_path &path, file_system_mounter mounter);
+
+  //path must be absolute. symlinks are always resolved on nodes other than the
+  //final one. they are resolved on the final node if and only if resolve final
+  //node is set to true. mount points are always traversed, including on the
+  //final node. this assumes that the path is under some mount point, and the
+  //same for any symlinks traversed (e.g. / is mounted).
+  io_result look_up_absolute_path(const canon_path &path, block_device *&bd_out,
+    node_id_t &node_out, bool resolve_final_node, canon_path &path_without_symlinks_out);
+
+}
+
+#endif
-- 
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