feat(fd): add fd table and register/destroy function

k/fd.c

@@ -0,0 +1,37 @@
+#include "fd.h"
+
+static struct file_entry fd_table[MAX_FD] = { 0 };
+
+static int find_next_fd(void)
+{
+    for (int fd = 0; fd < MAX_FD; ++fd)
+    {
+        if (!fd_table[fd].open)
+            return fd;
+    }
+
+    return -1;
+}
+
+int register_fd(u32 lba)
+{
+    int free_fd = find_next_fd();
+    if (free_fd < 0)
+        return -1;
+
+    struct file_entry f = { .open = 1, .lba = lba, .file_offset = 0 };
+    fd_table[free_fd] = f;
+    return free_fd;
+}
+
+int destroy_fd(int fd)
+{
+    if (fd > MAX_FD || !fd_table[fd].open)
+        return -1;
+
+    fd_table[fd].open = 0;
+    fd_table[fd].lba = 0;
+    fd_table[fd].file_offset = 0;
+
+    return 0;
+}

k/fd.h

@@ -0,0 +1,18 @@
+#ifndef FD_H
+#define FD_H
+
+#include <k/types.h>
+
+#define MAX_FD 65535
+
+struct file_entry
+{
+    u8 open;
+    u32 lba;
+    u64 file_offset;
+};
+
+int register_fd(u32 lba);
+int destroy_fd(int fd);
+
+#endif /* !FD_H */