1 files changed, 254 insertions, 0 deletions
diff --git a/kernel/storage/fs/tarfs.cpp b/kernel/storage/fs/tarfs.cpp
new file mode 100644
index 0000000..4b752a2
--- /dev/null
+++ b/kernel/storage/fs/tarfs.cpp
@@ -0,0 +1,254 @@
+#include <mercury/kernel/storage/fs/tarfs.hpp>
+
+//in tarfs_instance, node_id_t and directory_iter_t refer to the number
+//of bytes into the block device that the info sector is located.
+
+namespace mercury::kernel::storage::fs {
+
+#define BD_TO_FS(expr) \
+  { \
+    bd_result _result = expr; \
+    if (_result == bd_result::out_of_bounds) \
+      return fs_result::fs_corrupt; \
+    if (_result == bd_result::device_error) \
+      return fs_result::device_error; \
+  }
+
+#define FS_TO_FS(expr) \
+  { \
+    fs_result _result = expr; \
+    if (_result != fs_result::success) \
+      return _result; \
+  }
+
+  tarfs_instance::tarfs_instance(block_device *bd) : bd(bd) {}
+
+  fs_result tarfs_instance::next_node(
+    node_id_t node, std::optional<node_id_t> &out
+  ) {
+
+    uint64_t bytes;
+    FS_TO_FS(read_num(node + 124, 12, bytes))
+    out = node + ((bytes - 1) / 512 + 2) * 512;
+
+    uint8_t sector[512];
+    BD_TO_FS(bd->read_bytes(node, 512, sector))
+    for (unsigned i = 0; i < 512; ++i)
+      if (sector[i] != 0)
+        return fs_result::success;
+
+    out = {};
+    return fs_result::success;
+
+  }
+
+  fs_result tarfs_instance::read_full_name(
+    node_id_t node, utility::string &out
+  ) {
+
+    out.count = 0;
+    out.verify_buffer_len(155);
+    BD_TO_FS(bd->read_bytes(node + 345, 155, out.buffer))
+
+    while (out.count < 155 && out.buffer[out.count] != '\0')
+      ++out.count;
+
+    unsigned new_max = out.count + 100;
+    out.verify_buffer_len(new_max);
+    BD_TO_FS(bd->read_bytes(node, 100, out.buffer + out.count))
+
+    while (out.count < 255 && out.buffer[out.count] != '\0')
+      ++out.count;
+
+    return fs_result::success;
+
+  }
+
+  //len <= 12.
+  fs_result tarfs_instance::read_num(
+    uint64_t offset, unsigned len, uint64_t &out
+  ) {
+
+    char buf[12];
+    BD_TO_FS(bd->read_bytes(offset, len, buf))
+
+    out = 0;
+    for (unsigned i = 0; i < len && buf[i] != '\0'; ++i) {
+      if (buf[i] < '0' || buf[i] > '7')
+        return fs_result::fs_corrupt;
+      out = out * 8 + buf[i] - '0';
+    }
+
+    return fs_result::success;
+
+  }
+
+  fs_result tarfs_instance::first_child_starting_at(
+    node_id_t parent, node_id_t start, std::optional<node_id_t> &out
+  ) {
+
+    utility::string parent_full_name;
+    FS_TO_FS(read_full_name(parent, parent_full_name))
+
+    utility::string child_full_name;
+    out = start;
+
+    do {
+
+      FS_TO_FS(read_full_name(*out, child_full_name))
+
+      if (child_full_name.count > parent_full_name.count &&
+          child_full_name.starts_with(parent_full_name)
+      ) {
+        if (child_full_name.buffer[child_full_name.count - 1] == '/')
+          --child_full_name.count;
+        for (unsigned i = parent_full_name.count;
+             i < child_full_name.count; ++i)
+          if (child_full_name.buffer[i] == '/')
+            goto next;
+        return fs_result::success;
+      }
+
+    next:
+      next_node(*out, out);
+
+    } while (out);
+
+    return fs_result::success;
+
+  }
+
+  fs_result tarfs_instance::get_dir_entry(node_id_t node, dir_entry &entry) {
+
+    utility::string full_name;
+    read_full_name(node, full_name);
+
+    if (full_name.count == 2)
+      entry.name.count = 0;
+
+    else {
+
+      if (full_name.buffer[full_name.count - 1] == '/')
+        --full_name.count;
+
+      unsigned last_slash =
+        utility::find_last(full_name.buffer, full_name.count, '/');
+      entry.name.count = full_name.count - last_slash - 1;
+      entry.name.verify_buffer_len(entry.name.count);
+
+      for (unsigned i = 0; i < entry.name.count; ++i)
+        entry.name.buffer[i] = full_name.buffer[last_slash + 1 + i];
+
+    }
+
+    entry.node = node;
+
+    char ch;
+    BD_TO_FS(bd->read_bytes(node + 156, 1, &ch));
+    switch (ch) {
+      case '0':
+        entry.type = file_type::regular_file;
+        break;
+      case '2':
+        entry.type = file_type::symlink;
+        break;
+      case '5':
+        entry.type = file_type::directory;
+        break;
+      default:
+        return fs_result::fs_corrupt;
+    }
+
+    if (entry.type == file_type::regular_file) {
+      uint64_t length;
+      FS_TO_FS(read_num(node + 124, 12, length))
+      entry.length = length;
+    }
+
+    else if (entry.type == file_type::symlink) {
+      utility::string target;
+      target.verify_buffer_len(100);
+      BD_TO_FS(bd->read_bytes(node + 157, 100, target.buffer))
+      while (target.count < 100 && target.buffer[target.count] != '\0')
+        ++target.count;
+      entry.target = std::move(target);
+    }
+
+    return fs_result::success;
+
+  }
+
+  fs_result tarfs_instance::get_root_node(node_id_t &out) {
+
+    utility::string full_name;
+    std::optional<node_id_t> on = 0;
+
+    do {
+
+      FS_TO_FS(read_full_name(*on, full_name))
+      if (full_name.count == 2) {
+        out = *on;
+        return fs_result::success;
+      }
+      next_node(*on, on);
+
+    } while (on);
+
+    return fs_result::fs_corrupt;
+
+  }
+
+  fs_result tarfs_instance::get_first_child(
+    node_id_t node, std::optional<dir_entry> &out, directory_iter_t &iter_out
+  ) {
+
+    std::optional<node_id_t> child;
+    FS_TO_FS(first_child_starting_at(node, 0, child))
+    if (!child) {
+      out = {};
+      return fs_result::success;
+    }
+
+    dir_entry entry;
+    FS_TO_FS(get_dir_entry(*child, entry))
+    out = std::move(entry);
+    iter_out = (directory_iter_t)*child;
+    return fs_result::success;
+
+  }
+
+  fs_result tarfs_instance::get_next_child(
+    node_id_t node, std::optional<dir_entry> &out, directory_iter_t &iter
+  ) {
+
+    std::optional<node_id_t> start;
+    FS_TO_FS(next_node((node_id_t)iter, start))
+    if (!start) {
+      out = {};
+      return fs_result::success;
+    }
+
+    std::optional<node_id_t> child;
+    FS_TO_FS(first_child_starting_at(node, *start, child))
+    if (!child) {
+      out = {};
+      return fs_result::success;
+    }
+
+    dir_entry entry;
+    FS_TO_FS(get_dir_entry(*child, entry))
+    out = std::move(entry);
+    iter = (directory_iter_t)*child;
+    return fs_result::success;
+
+  }
+
+  fs_result tarfs_instance::read_bytes_from_file(
+    node_id_t node, uint64_t start, uint64_t count, void *into
+  ) {
+    BD_TO_FS(bd->read_bytes(node + 512 + start, count, into))
+    return fs_result::success;
+  }
+
+
+}