text: /*
   * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <Kernel/Debug.h>
  #include <Kernel/FileSystem/OpenFileDescription.h>
  #include <Kernel/Process.h>
  
  namespace Kernel {
  
  using BlockFlags = Thread::FileBlocker::BlockFlags;
  
  static ErrorOr<NonnullRefPtr<OpenFileDescription>> open_readable_file_description(auto& fds, int fd)
  {
      auto description = TRY(fds.with_shared([&](auto& fds) { return fds.open_file_description(fd); }));
      if (!description->is_readable())
          return EBADF;
      if (description->is_directory())
          return EISDIR;
      return description;
  }
  
  static ErrorOr<void> check_blocked_read(OpenFileDescription* description)
  {
      if (description->is_blocking()) {
          if (!description->can_read()) {
              auto unblock_flags = BlockFlags::None;
              if (Thread::current()->block<Thread::ReadBlocker>({}, *description, unblock_flags).was_interrupted())
                  return EINTR;
              if (!has_flag(unblock_flags, BlockFlags::Read))
                  return EAGAIN;
              // TODO: handle exceptions in unblock_flags
          }
      }
      return {};
  }
  
  ErrorOr<FlatPtr> Process::sys$readv(int fd, Userspace<const struct iovec*> iov, int iov_count)
  {
      VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
      TRY(require_promise(Pledge::stdio));
      if (iov_count < 0)
          return EINVAL;
  
      // Arbitrary pain threshold.
      if (iov_count > (int)MiB)
          return EFAULT;
  
      u64 total_length = 0;
      Vector<iovec, 32> vecs;
      TRY(vecs.try_resize(iov_count));
      TRY(copy_n_from_user(vecs.data(), iov, iov_count));
      for (auto& vec : vecs) {
          total_length += vec.iov_len;
          if (total_length > NumericLimits<i32>::max())
              return EINVAL;
      }
  
      auto description = TRY(open_readable_file_description(fds(), fd));
  
      int nread = 0;
      for (auto& vec : vecs) {
          TRY(check_blocked_read(description));
          auto buffer = TRY(UserOrKernelBuffer::for_user_buffer((u8*)vec.iov_base, vec.iov_len));
          auto nread_here = TRY(description->read(buffer, vec.iov_len));
          nread += nread_here;
      }
  
      return nread;
  }
  
  ErrorOr<FlatPtr> Process::sys$read(int fd, Userspace<u8*> buffer, size_t size)
  {
      VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
      TRY(require_promise(Pledge::stdio));
      if (size == 0)
          return 0;
      if (size > NumericLimits<ssize_t>::max())
          return EINVAL;
      dbgln_if(IO_DEBUG, "sys$read({}, {}, {})", fd, buffer.ptr(), size);
      auto description = TRY(open_readable_file_description(fds(), fd));
      TRY(check_blocked_read(description));
      auto user_buffer = TRY(UserOrKernelBuffer::for_user_buffer(buffer, size));
      return TRY(description->read(user_buffer, size));
  }
  
  // NOTE: The offset is passed by pointer because off_t is 64bit,
  // hence it can't be passed by register on 32bit platforms.
  ErrorOr<FlatPtr> Process::sys$pread(int fd, Userspace<u8*> buffer, size_t size, Userspace<off_t const*> userspace_offset)
  {
      VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
      TRY(require_promise(Pledge::stdio));
      if (size == 0)
          return 0;
      if (size > NumericLimits<ssize_t>::max())
          return EINVAL;
      auto offset = TRY(copy_typed_from_user(userspace_offset));
      if (offset < 0)
          return EINVAL;
      dbgln_if(IO_DEBUG, "sys$pread({}, {}, {}, {})", fd, buffer.ptr(), size, offset);
      auto description = TRY(open_readable_file_description(fds(), fd));
      if (!description->file().is_seekable())
          return EINVAL;
      TRY(check_blocked_read(description));
      auto user_buffer = TRY(UserOrKernelBuffer::for_user_buffer(buffer, size));
      return TRY(description->read(user_buffer, offset, size));
  }
  
  }
  