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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>struct usb_request</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="USB Gadget API for Linux" /><link rel="up" href="ch03s03.html" title="Core Objects and Methods" /><link rel="prev" href="ch03s03.html" title="Core Objects and Methods" /><link rel="next" href="re17.html" title="struct usb_ep" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span>struct usb_request</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch03s03.html">Prev</a> </td><th width="60%" align="center">Core Objects and Methods</th><td width="20%" align="right"> <a accesskey="n" href="re17.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="struct usb_request"><a id="API-struct-usb-request"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>struct usb_request —
describes one i/o request
</p></div><div class="refsynopsisdiv" title="Synopsis"><h2>Synopsis</h2><pre class="programlisting">
struct usb_request {
void * buf;
unsigned length;
dma_addr_t dma;
unsigned no_interrupt:1;
unsigned zero:1;
unsigned short_not_ok:1;
void (* complete) (struct usb_ep *ep,struct usb_request *req);
void * context;
struct list_head list;
int status;
unsigned actual;
}; </pre></div><div class="refsect1" title="Members"><a id="id2938945"></a><h2>Members</h2><div class="variablelist"><dl><dt><span class="term">buf</span></dt><dd><p>
Buffer used for data. Always provide this; some controllers
only use PIO, or don't use DMA for some endpoints.
</p></dd><dt><span class="term">length</span></dt><dd><p>
Length of that data
</p></dd><dt><span class="term">dma</span></dt><dd><p>
DMA address corresponding to 'buf'. If you don't set this
field, and the usb controller needs one, it is responsible
for mapping and unmapping the buffer.
</p></dd><dt><span class="term">no_interrupt</span></dt><dd><p>
If true, hints that no completion irq is needed.
Helpful sometimes with deep request queues that are handled
directly by DMA controllers.
</p></dd><dt><span class="term">zero</span></dt><dd><p>
If true, when writing data, makes the last packet be <span class="quote">“<span class="quote">short</span>”</span>
by adding a zero length packet as needed;
</p></dd><dt><span class="term">short_not_ok</span></dt><dd><p>
When reading data, makes short packets be
treated as errors (queue stops advancing till cleanup).
</p></dd><dt><span class="term">complete</span></dt><dd><p>
Function called when request completes, so this request and
its buffer may be re-used. The function will always be called with
interrupts disabled, and it must not sleep.
Reads terminate with a short packet, or when the buffer fills,
whichever comes first. When writes terminate, some data bytes
will usually still be in flight (often in a hardware fifo).
Errors (for reads or writes) stop the queue from advancing
until the completion function returns, so that any transfers
invalidated by the error may first be dequeued.
</p></dd><dt><span class="term">context</span></dt><dd><p>
For use by the completion callback
</p></dd><dt><span class="term">list</span></dt><dd><p>
For use by the gadget driver.
</p></dd><dt><span class="term">status</span></dt><dd><p>
Reports completion code, zero or a negative errno.
Normally, faults block the transfer queue from advancing until
the completion callback returns.
Code <span class="quote">“<span class="quote">-ESHUTDOWN</span>”</span> indicates completion caused by device disconnect,
or when the driver disabled the endpoint.
</p></dd><dt><span class="term">actual</span></dt><dd><p>
Reports bytes transferred to/from the buffer. For reads (OUT
transfers) this may be less than the requested length. If the
short_not_ok flag is set, short reads are treated as errors
even when status otherwise indicates successful completion.
Note that for writes (IN transfers) some data bytes may still
reside in a device-side FIFO when the request is reported as
complete.
</p></dd></dl></div></div><div class="refsect1" title="Description"><a id="id2939111"></a><h2>Description</h2><p>
These are allocated/freed through the endpoint they're used with. The
hardware's driver can add extra per-request data to the memory it returns,
which often avoids separate memory allocations (potential failures),
later when the request is queued.
</p><p>
Request flags affect request handling, such as whether a zero length
packet is written (the <span class="quote">“<span class="quote">zero</span>”</span> flag), whether a short read should be
treated as an error (blocking request queue advance, the <span class="quote">“<span class="quote">short_not_ok</span>”</span>
flag), or hinting that an interrupt is not required (the <span class="quote">“<span class="quote">no_interrupt</span>”</span>
flag, for use with deep request queues).
</p><p>
Bulk endpoints can use any size buffers, and can also be used for interrupt
transfers. interrupt-only endpoints can be much less functional.
</p></div><div class="refsect1" title="NOTE"><a id="id2939147"></a><h2>NOTE</h2><p>
this is analagous to 'struct urb' on the host side, except that
it's thinner and promotes more pre-allocation.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch03s03.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch03s03.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="re17.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Core Objects and Methods </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> <span>struct usb_ep</span></td></tr></table></div></body></html>
