glib/docs/reference/gio/overview.xml

<part>
  <title>GIO Overview</title>

  <para>
    GIO is striving to provide a modern, easy-to-use VFS api that sits
    at the right level in the library stack. The goal is to overcome the
    shortcomings of gnome-vfs and provide an api that is so good that
    developers prefer it over raw POSIX calls. Among other things
    that means using GObject. It also means not cloning the POSIX 
    api, but providing a higher-level, document-centric interfaces.
  </para>

  <para>
    The abstract file system model of GIO consists of a number of
    interfaces and base classes for I/O and files:
    <variablelist>
       <varlistentry>
         <term>GFile</term>
         <listitem><para>reference to a file</para></listitem>
       </varlistentry>
       <varlistentry>
         <term>GFileInfo</term>
         <listitem><para>information about a file or filesystem</para></listitem>
       </varlistentry>
       <varlistentry>
         <term>GFileEnumerator</term>
         <listitem><para>list files in directories</para></listitem>
       </varlistentry>
       <varlistentry>
         <term>GDrive</term>
         <listitem><para>represents a drive</para></listitem>
       </varlistentry>
       <varlistentry>
         <term>GVolume</term>
         <listitem><para>represents a file system in an abstract way</para></listitem>
       </varlistentry>
       <varlistentry>
         <term>GMount</term>
         <listitem><para>represents a mounted file system</para></listitem>
       </varlistentry>
    </variablelist>
    Then there is a number of stream classes, similar to the input and
    output stream hierarchies that can be found in frameworks like Java:
    <variablelist>
       <varlistentry>
         <term>GInputStream</term>
         <listitem><para>read data</para></listitem>
       </varlistentry>
       <varlistentry>
         <term>GOutputStream</term>
         <listitem><para>write data</para></listitem>
       </varlistentry>
       <varlistentry>
         <term>GSeekable</term>
         <listitem><para>seek in data</para></listitem>
       </varlistentry>
    </variablelist>
    There are interfaces related to applications and the types
    of files they handle:
    <variablelist>
       <varlistentry>
          <term>GAppInfo</term>
          <listitem><para>information about an installed application</para></listitem>
       </varlistentry>
       <varlistentry>
          <term>GIcon</term>
          <listitem><para>abstract type for file and application icons</para></listitem>
       </varlistentry>
    </variablelist>
    Beyond these, GIO provides facilities for file monitoring,
    asynchronous I/O and filename completion.  In addition to the 
    interfaces, GIO provides implementations for the local case. 
    Implementations for various network file systems are provided 
    by the GVFS package as loadable modules.
  </para>

  <para>
    Other design choices which consciously break with the gnome-vfs
    design are to move backends out-of-process, which minimizes the
    dependency bloat and makes the whole system more robust. The backends
    are not included in GIO, but in the separate GVFS package. GVFS 
    also contains the GVFS daemon, which spawn further mount daemons 
    for each individual connection.
  </para>

  <para>
    <figure id="mainloop-states">
      <title>GIO in the GTK+ library stack</title>
      <graphic fileref="gvfs-overview.png" format="PNG"></graphic>
    </figure>
  </para>

  <para>
    The GIO model of I/O is stateful: if an application establishes e.g. 
    a sftp connection to a server, it becomes available to all applications 
    in the session; the user does not have to enter his password over 
    and over again.
  </para>
  <para>
    One of the big advantages of putting the VFS in the GLib layer 
    is that GTK+ can directly use it, e.g. in the filechooser.
  </para>

</part>