<html lang="en">
<head>
<title>Host I/O Packets - Debugging with GDB</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="Debugging with GDB">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="Remote-Protocol.html#Remote-Protocol" title="Remote Protocol">
<link rel="prev" href="Tracepoint-Packets.html#Tracepoint-Packets" title="Tracepoint Packets">
<link rel="next" href="Interrupts.html#Interrupts" title="Interrupts">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 1988-2019 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``Free Software'' and ``Free Software Needs
Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
and with the Back-Cover Texts as in (a) below.

(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom.''
-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
  pre.display { font-family:inherit }
  pre.format  { font-family:inherit }
  pre.smalldisplay { font-family:inherit; font-size:smaller }
  pre.smallformat  { font-family:inherit; font-size:smaller }
  pre.smallexample { font-size:smaller }
  pre.smalllisp    { font-size:smaller }
  span.sc    { font-variant:small-caps }
  span.roman { font-family:serif; font-weight:normal; } 
  span.sansserif { font-family:sans-serif; font-weight:normal; } 
--></style>
</head>
<body>
<div class="node">
<a name="Host-I%2fO-Packets"></a>
<a name="Host-I_002fO-Packets"></a>
<p>
Next:&nbsp;<a rel="next" accesskey="n" href="Interrupts.html#Interrupts">Interrupts</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="Tracepoint-Packets.html#Tracepoint-Packets">Tracepoint Packets</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="Remote-Protocol.html#Remote-Protocol">Remote Protocol</a>
<hr>
</div>

<h3 class="section">E.7 Host I/O Packets</h3>

<p><a name="index-Host-I_002fO_002c-remote-protocol-3587"></a><a name="index-file-transfer_002c-remote-protocol-3588"></a>
The <dfn>Host I/O</dfn> packets allow <span class="sc">gdb</span> to perform I/O
operations on the far side of a remote link.  For example, Host I/O is
used to upload and download files to a remote target with its own
filesystem.  Host I/O uses the same constant values and data structure
layout as the target-initiated File-I/O protocol.  However, the
Host I/O packets are structured differently.  The target-initiated
protocol relies on target memory to store parameters and buffers. 
Host I/O requests are initiated by <span class="sc">gdb</span>, and the
target's memory is not involved.  See <a href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension">File-I/O Remote Protocol Extension</a>, for more details on the target-initiated protocol.

   <p>The Host I/O request packets all encode a single operation along with
its arguments.  They have this format:

     <dl>
<dt>&lsquo;<samp><span class="samp">vFile:</span><var>operation</var><span class="samp">: </span><var>parameter</var><span class="samp">...</span></samp>&rsquo;<dd><var>operation</var> is the name of the particular request; the target
should compare the entire packet name up to the second colon when checking
for a supported operation.  The format of <var>parameter</var> depends on
the operation.  Numbers are always passed in hexadecimal.  Negative
numbers have an explicit minus sign (i.e. two's complement is not
used).  Strings (e.g. filenames) are encoded as a series of
hexadecimal bytes.  The last argument to a system call may be a
buffer of escaped binary data (see <a href="Binary-Data.html#Binary-Data">Binary Data</a>).

   </dl>

   <p>The valid responses to Host I/O packets are:

     <dl>
<dt>&lsquo;<samp><span class="samp">F </span><var>result</var><span class="samp"> [, </span><var>errno</var><span class="samp">] [; </span><var>attachment</var><span class="samp">]</span></samp>&rsquo;<dd><var>result</var> is the integer value returned by this operation, usually
non-negative for success and -1 for errors.  If an error has occured,
<var>errno</var> will be included in the result specifying a
value defined by the File-I/O protocol (see <a href="Errno-Values.html#Errno-Values">Errno Values</a>).  For
operations which return data, <var>attachment</var> supplies the data as a
binary buffer.  Binary buffers in response packets are escaped in the
normal way (see <a href="Binary-Data.html#Binary-Data">Binary Data</a>).  See the individual packet
documentation for the interpretation of <var>result</var> and
<var>attachment</var>.

     <br><dt>&lsquo;<samp><span class="samp"><!-- /@w --></span></samp>&rsquo;<dd>An empty response indicates that this operation is not recognized.

   </dl>

   <p>These are the supported Host I/O operations:

     <dl>
<dt>&lsquo;<samp><span class="samp">vFile:open: </span><var>filename</var><span class="samp">, </span><var>flags</var><span class="samp">, </span><var>mode</var></samp>&rsquo;<dd>Open a file at <var>filename</var> and return a file descriptor for it, or
return -1 if an error occurs.  The <var>filename</var> is a string,
<var>flags</var> is an integer indicating a mask of open flags
(see <a href="Open-Flags.html#Open-Flags">Open Flags</a>), and <var>mode</var> is an integer indicating a mask
of mode bits to use if the file is created (see <a href="mode_005ft-Values.html#mode_005ft-Values">mode_t Values</a>). 
See <a href="open.html#open">open</a>, for details of the open flags and mode values.

     <br><dt>&lsquo;<samp><span class="samp">vFile:close: </span><var>fd</var></samp>&rsquo;<dd>Close the open file corresponding to <var>fd</var> and return 0, or
-1 if an error occurs.

     <br><dt>&lsquo;<samp><span class="samp">vFile:pread: </span><var>fd</var><span class="samp">, </span><var>count</var><span class="samp">, </span><var>offset</var></samp>&rsquo;<dd>Read data from the open file corresponding to <var>fd</var>.  Up to
<var>count</var> bytes will be read from the file, starting at <var>offset</var>
relative to the start of the file.  The target may read fewer bytes;
common reasons include packet size limits and an end-of-file
condition.  The number of bytes read is returned.  Zero should only be
returned for a successful read at the end of the file, or if
<var>count</var> was zero.

     <p>The data read should be returned as a binary attachment on success. 
If zero bytes were read, the response should include an empty binary
attachment (i.e. a trailing semicolon).  The return value is the
number of target bytes read; the binary attachment may be longer if
some characters were escaped.

     <br><dt>&lsquo;<samp><span class="samp">vFile:pwrite: </span><var>fd</var><span class="samp">, </span><var>offset</var><span class="samp">, </span><var>data</var></samp>&rsquo;<dd>Write <var>data</var> (a binary buffer) to the open file corresponding
to <var>fd</var>.  Start the write at <var>offset</var> from the start of the
file.  Unlike many <code>write</code> system calls, there is no
separate <var>count</var> argument; the length of <var>data</var> in the
packet is used.  &lsquo;<samp><span class="samp">vFile:write</span></samp>&rsquo; returns the number of bytes written,
which may be shorter than the length of <var>data</var>, or -1 if an
error occurred.

     <br><dt>&lsquo;<samp><span class="samp">vFile:fstat: </span><var>fd</var></samp>&rsquo;<dd>Get information about the open file corresponding to <var>fd</var>. 
On success the information is returned as a binary attachment
and the return value is the size of this attachment in bytes. 
If an error occurs the return value is -1.  The format of the
returned binary attachment is as described in <a href="struct-stat.html#struct-stat">struct stat</a>.

     <br><dt>&lsquo;<samp><span class="samp">vFile:unlink: </span><var>filename</var></samp>&rsquo;<dd>Delete the file at <var>filename</var> on the target.  Return 0,
or -1 if an error occurs.  The <var>filename</var> is a string.

     <br><dt>&lsquo;<samp><span class="samp">vFile:readlink: </span><var>filename</var></samp>&rsquo;<dd>Read value of symbolic link <var>filename</var> on the target.  Return
the number of bytes read, or -1 if an error occurs.

     <p>The data read should be returned as a binary attachment on success. 
If zero bytes were read, the response should include an empty binary
attachment (i.e. a trailing semicolon).  The return value is the
number of target bytes read; the binary attachment may be longer if
some characters were escaped.

     <br><dt>&lsquo;<samp><span class="samp">vFile:setfs: </span><var>pid</var></samp>&rsquo;<dd>Select the filesystem on which <code>vFile</code> operations with
<var>filename</var> arguments will operate.  This is required for
<span class="sc">gdb</span> to be able to access files on remote targets where
the remote stub does not share a common filesystem with the
inferior(s).

     <p>If <var>pid</var> is nonzero, select the filesystem as seen by process
<var>pid</var>.  If <var>pid</var> is zero, select the filesystem as seen by
the remote stub.  Return 0 on success, or -1 if an error occurs. 
If <code>vFile:setfs:</code> indicates success, the selected filesystem
remains selected until the next successful <code>vFile:setfs:</code>
operation.

   </dl>

   </body></html>