1<html><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 V1.78.1"><link rel="home" href="index.html" title="USB Gadget API for Linux"><link rel="up" href="core.html" title="Core Objects and Methods"><link rel="prev" href="core.html" title="Core Objects and Methods"><link rel="next" href="API-struct-usb-ep.html" title="struct usb_ep"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span class="phrase">struct usb_request</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="core.html">Prev</a> </td><th width="60%" align="center">Core Objects and Methods</th><td width="20%" align="right"> <a accesskey="n" href="API-struct-usb-ep.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="API-struct-usb-request"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>struct usb_request — 2 describes one i/o request 3 </p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="programlisting"> 4struct usb_request { 5 void * buf; 6 unsigned length; 7 dma_addr_t dma; 8 struct scatterlist * sg; 9 unsigned num_sgs; 10 unsigned num_mapped_sgs; 11 unsigned stream_id:16; 12 unsigned no_interrupt:1; 13 unsigned zero:1; 14 unsigned short_not_ok:1; 15 void (* complete) (struct usb_ep *ep,struct usb_request *req); 16 void * context; 17 struct list_head list; 18 int status; 19 unsigned actual; 20}; </pre></div><div class="refsect1"><a name="idp1121049580"></a><h2>Members</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term">buf</span></dt><dd><p> 21Buffer used for data. Always provide this; some controllers 22only use PIO, or don't use DMA for some endpoints. 23 </p></dd><dt><span class="term">length</span></dt><dd><p> 24Length of that data 25 </p></dd><dt><span class="term">dma</span></dt><dd><p> 26DMA address corresponding to 'buf'. If you don't set this 27field, and the usb controller needs one, it is responsible 28for mapping and unmapping the buffer. 29 </p></dd><dt><span class="term">sg</span></dt><dd><p> 30a scatterlist for SG-capable controllers. 31 </p></dd><dt><span class="term">num_sgs</span></dt><dd><p> 32number of SG entries 33 </p></dd><dt><span class="term">num_mapped_sgs</span></dt><dd><p> 34number of SG entries mapped to DMA (internal) 35 </p></dd><dt><span class="term">stream_id</span></dt><dd><p> 36The stream id, when USB3.0 bulk streams are being used 37 </p></dd><dt><span class="term">no_interrupt</span></dt><dd><p> 38If true, hints that no completion irq is needed. 39Helpful sometimes with deep request queues that are handled 40directly by DMA controllers. 41 </p></dd><dt><span class="term">zero</span></dt><dd><p> 42If true, when writing data, makes the last packet be <span class="quote">“<span class="quote">short</span>”</span> 43by adding a zero length packet as needed; 44 </p></dd><dt><span class="term">short_not_ok</span></dt><dd><p> 45When reading data, makes short packets be 46treated as errors (queue stops advancing till cleanup). 47 </p></dd><dt><span class="term">complete</span></dt><dd><p> 48Function called when request completes, so this request and 49its buffer may be re-used. The function will always be called with 50interrupts disabled, and it must not sleep. 51Reads terminate with a short packet, or when the buffer fills, 52whichever comes first. When writes terminate, some data bytes 53will usually still be in flight (often in a hardware fifo). 54Errors (for reads or writes) stop the queue from advancing 55until the completion function returns, so that any transfers 56invalidated by the error may first be dequeued. 57 </p></dd><dt><span class="term">context</span></dt><dd><p> 58For use by the completion callback 59 </p></dd><dt><span class="term">list</span></dt><dd><p> 60For use by the gadget driver. 61 </p></dd><dt><span class="term">status</span></dt><dd><p> 62Reports completion code, zero or a negative errno. 63Normally, faults block the transfer queue from advancing until 64the completion callback returns. 65Code <span class="quote">“<span class="quote">-ESHUTDOWN</span>”</span> indicates completion caused by device disconnect, 66or when the driver disabled the endpoint. 67 </p></dd><dt><span class="term">actual</span></dt><dd><p> 68Reports bytes transferred to/from the buffer. For reads (OUT 69transfers) this may be less than the requested length. If the 70short_not_ok flag is set, short reads are treated as errors 71even when status otherwise indicates successful completion. 72Note that for writes (IN transfers) some data bytes may still 73reside in a device-side FIFO when the request is reported as 74complete. 75 </p></dd></dl></div></div><div class="refsect1"><a name="idp1123935988"></a><h2>Description</h2><p> 76 These are allocated/freed through the endpoint they're used with. The 77 hardware's driver can add extra per-request data to the memory it returns, 78 which often avoids separate memory allocations (potential failures), 79 later when the request is queued. 80 </p><p> 81 82 Request flags affect request handling, such as whether a zero length 83 packet is written (the <span class="quote">“<span class="quote">zero</span>”</span> flag), whether a short read should be 84 treated as an error (blocking request queue advance, the <span class="quote">“<span class="quote">short_not_ok</span>”</span> 85 flag), or hinting that an interrupt is not required (the <span class="quote">“<span class="quote">no_interrupt</span>”</span> 86 flag, for use with deep request queues). 87 </p><p> 88 89 Bulk endpoints can use any size buffers, and can also be used for interrupt 90 transfers. interrupt-only endpoints can be much less functional. 91</p></div><div class="refsect1"><a name="idp1123938172"></a><h2>NOTE</h2><p> 92 this is analogous to 'struct urb' on the host side, except that 93 it's thinner and promotes more pre-allocation. 94</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="core.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="core.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="API-struct-usb-ep.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 class="phrase">struct usb_ep</span></td></tr></table></div></body></html> 95