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<a name="File_002dI_002fO-Overview"></a>
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Next: <a href="Protocol-Basics.html#Protocol-Basics" accesskey="n" rel="next">Protocol Basics</a>, Up: <a href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension" accesskey="u" rel="up">File-I/O Remote Protocol Extension</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<a name="File_002dI_002fO-Overview-1"></a>
<h4 class="subsection">E.13.1 File-I/O Overview</h4>
<a name="index-file_002di_002fo-overview"></a>

<p>The <em>File I/O remote protocol extension</em> (short: File-I/O) allows the
target to use the host&rsquo;s file system and console I/O to perform various
system calls.  System calls on the target system are translated into a
remote protocol packet to the host system, which then performs the needed
actions and returns a response packet to the target system.
This simulates file system operations even on targets that lack file systems.
</p>
<p>The protocol is defined to be independent of both the host and target systems.
It uses its own internal representation of datatypes and values.  Both
<small>GDB</small> and the target&rsquo;s <small>GDB</small> stub are responsible for
translating the system-dependent value representations into the internal
protocol representations when data is transmitted.
</p>
<p>The communication is synchronous.  A system call is possible only when 
<small>GDB</small> is waiting for a response from the &lsquo;<samp>C</samp>&rsquo;, &lsquo;<samp>c</samp>&rsquo;, &lsquo;<samp>S</samp>&rsquo; 
or &lsquo;<samp>s</samp>&rsquo; packets.  While <small>GDB</small> handles the request for a system call,
the target is stopped to allow deterministic access to the target&rsquo;s
memory.  Therefore File-I/O is not interruptible by target signals.  On
the other hand, it is possible to interrupt File-I/O by a user interrupt 
(&lsquo;<samp>Ctrl-C</samp>&rsquo;) within <small>GDB</small>.
</p>
<p>The target&rsquo;s request to perform a host system call does not finish
the latest &lsquo;<samp>C</samp>&rsquo;, &lsquo;<samp>c</samp>&rsquo;, &lsquo;<samp>S</samp>&rsquo; or &lsquo;<samp>s</samp>&rsquo; action.  That means,
after finishing the system call, the target returns to continuing the
previous activity (continue, step).  No additional continue or step
request from <small>GDB</small> is required.
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) continue
  &lt;- target requests 'system call X'
  target is stopped, GDB executes system call
  -&gt; GDB returns result
  ... target continues, GDB returns to wait for the target
  &lt;- target hits breakpoint and sends a Txx packet
</pre></div>

<p>The protocol only supports I/O on the console and to regular files on 
the host file system.  Character or block special devices, pipes,
named pipes, sockets or any other communication method on the host
system are not supported by this protocol.
</p>
<p>File I/O is not supported in non-stop mode.
</p>
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Next: <a href="Protocol-Basics.html#Protocol-Basics" accesskey="n" rel="next">Protocol Basics</a>, Up: <a href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension" accesskey="u" rel="up">File-I/O Remote Protocol Extension</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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