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| <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>‘<samp><span class="samp">vFile:</span><var>operation</var><span class="samp">: </span><var>parameter</var><span class="samp">...</span></samp>’<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>‘<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>’<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>‘<samp><span class="samp"><!-- /@w --></span></samp>’<dd>An empty response indicates that this operation is not recognized. |
| |
| </dl> |
| |
| <p>These are the supported Host I/O operations: |
| |
| <dl> |
| <dt>‘<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>’<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>‘<samp><span class="samp">vFile:close: </span><var>fd</var></samp>’<dd>Close the open file corresponding to <var>fd</var> and return 0, or |
| -1 if an error occurs. |
| |
| <br><dt>‘<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>’<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>‘<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>’<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. ‘<samp><span class="samp">vFile:write</span></samp>’ 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>‘<samp><span class="samp">vFile:fstat: </span><var>fd</var></samp>’<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>‘<samp><span class="samp">vFile:unlink: </span><var>filename</var></samp>’<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>‘<samp><span class="samp">vFile:readlink: </span><var>filename</var></samp>’<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>‘<samp><span class="samp">vFile:setfs: </span><var>pid</var></samp>’<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> |
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