<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>How commands are completed</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="libATA Developer's Guide" /><link rel="up" href="ch03.html" title="Chapter 3. Error handling" /><link rel="prev" href="ch03s03.html" title="How commands are processed" /><link rel="next" href="ch03s05.html" title="ata_scsi_error()" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">How commands are completed</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch03s03.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Error handling</th><td width="20%" align="right"> <a accesskey="n" href="ch03s05.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="How commands are completed"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2810938"></a>How commands are completed</h2></div></div></div><p> Once issued, all qc's are either completed with ata_qc_complete() or time out. For commands which are handled by interrupts, ata_host_intr() invokes ata_qc_complete(), and, for PIO tasks, pio_task invokes ata_qc_complete(). In error cases, packet_task may also complete commands. </p><p> ata_qc_complete() does the following. </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p> DMA memory is unmapped. </p></li><li class="listitem"><p> ATA_QCFLAG_ACTIVE is clared from qc->flags. </p></li><li class="listitem"><p> qc->complete_fn() callback is invoked. If the return value of the callback is not zero. Completion is short circuited and ata_qc_complete() returns. </p></li><li class="listitem"><p> __ata_qc_complete() is called, which does </p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p> qc->flags is cleared to zero. </p></li><li class="listitem"><p> ap->active_tag and qc->tag are poisoned. </p></li><li class="listitem"><p> qc->waiting is claread & completed (in that order). </p></li><li class="listitem"><p> qc is deallocated by clearing appropriate bit in ap->qactive. </p></li></ol></div><p> </p></li></ol></div><p> So, it basically notifies upper layer and deallocates qc. One exception is short-circuit path in #3 which is used by atapi_qc_complete(). </p><p> For all non-ATAPI commands, whether it fails or not, almost the same code path is taken and very little error handling takes place. A qc is completed with success status if it succeeded, with failed status otherwise. </p><p> However, failed ATAPI commands require more handling as REQUEST SENSE is needed to acquire sense data. If an ATAPI command fails, ata_qc_complete() is invoked with error status, which in turn invokes atapi_qc_complete() via qc->complete_fn() callback. </p><p> This makes atapi_qc_complete() set scmd->result to SAM_STAT_CHECK_CONDITION, complete the scmd and return 1. As the sense data is empty but scmd->result is CHECK CONDITION, SCSI midlayer will invoke EH for the scmd, and returning 1 makes ata_qc_complete() to return without deallocating the qc. This leads us to ata_scsi_error() with partially completed qc. </p></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="ch03.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch03s05.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">How commands are processed </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> ata_scsi_error()</td></tr></table></div></body></html>
