ALSA: Update the documentation for changes of proc files

]]>

        </programlisting>

      </informalexample>

      For the raw data, <structfield>size</structfield> field must be

      set properly.  This specifies the maximum size of the proc file access.

    </para>

    <para>

      The callback is much more complicated than the text-file

      version. You need to use a low-level I/O functions such as

      The read/write callbacks of raw mode are more direct than the text mode.

      You need to use a low-level I/O functions such as

      <function>copy_from/to_user()</function> to transfer the

      data.

      <informalexample>

        <programlisting>

<![CDATA[

  static long my_file_io_read(struct snd_info_entry *entry,

  static ssize_t my_file_io_read(struct snd_info_entry *entry,

                              void *file_private_data,

                              struct file *file,

                              char *buf,

                              unsigned long count,

                              unsigned long pos)

                              size_t count,

                              loff_t pos)

  {

          long size = count;

          if (pos + size > local_max_size)

                  size = local_max_size - pos;

          if (copy_to_user(buf, local_data + pos, size))

          if (copy_to_user(buf, local_data + pos, count))

                  return -EFAULT;

          return size;

          return count;

  }

]]>

        </programlisting>

      </informalexample>

      If the size of the info entry has been set up properly,

      <structfield>count</structfield> and <structfield>pos</structfield> are

      guaranteed to fit within 0 and the given size.

      You don't have to check the range in the callbacks unless any

      other condition is required.

    </para>

  </chapter>