1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>How commands are issued</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="libATA Developer's Guide"><link rel="up" href="libataEH.html" title="Chapter 3. Error handling"><link rel="prev" href="libataEH.html" title="Chapter 3. Error handling"><link rel="next" href="ch03s03.html" title="How commands are processed"></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">How commands are issued</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="libataEH.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Error handling</th><td width="20%" align="right"> <a accesskey="n" href="ch03s03.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1120614212"></a>How commands are issued</h2></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">Internal commands</span></dt><dd><p> 2 First, qc is allocated and initialized using 3 ata_qc_new_init(). Although ata_qc_new_init() doesn't 4 implement any wait or retry mechanism when qc is not 5 available, internal commands are currently issued only during 6 initialization and error recovery, so no other command is 7 active and allocation is guaranteed to succeed. 8 </p><p> 9 Once allocated qc's taskfile is initialized for the command to 10 be executed. qc currently has two mechanisms to notify 11 completion. One is via qc->complete_fn() callback and the 12 other is completion qc->waiting. qc->complete_fn() callback 13 is the asynchronous path used by normal SCSI translated 14 commands and qc->waiting is the synchronous (issuer sleeps in 15 process context) path used by internal commands. 16 </p><p> 17 Once initialization is complete, host_set lock is acquired 18 and the qc is issued. 19 </p></dd><dt><span class="term">SCSI commands</span></dt><dd><p> 20 All libata drivers use ata_scsi_queuecmd() as 21 hostt->queuecommand callback. scmds can either be simulated 22 or translated. No qc is involved in processing a simulated 23 scmd. The result is computed right away and the scmd is 24 completed. 25 </p><p> 26 For a translated scmd, ata_qc_new_init() is invoked to 27 allocate a qc and the scmd is translated into the qc. SCSI 28 midlayer's completion notification function pointer is stored 29 into qc->scsidone. 30 </p><p> 31 qc->complete_fn() callback is used for completion 32 notification. ATA commands use ata_scsi_qc_complete() while 33 ATAPI commands use atapi_qc_complete(). Both functions end up 34 calling qc->scsidone to notify upper layer when the qc is 35 finished. After translation is completed, the qc is issued 36 with ata_qc_issue(). 37 </p><p> 38 Note that SCSI midlayer invokes hostt->queuecommand while 39 holding host_set lock, so all above occur while holding 40 host_set lock. 41 </p></dd></dl></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="libataEH.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="libataEH.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch03s03.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 3. Error handling </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> How commands are processed</td></tr></table></div></body></html> 42