220 lines
3.6 KiB
HTML
220 lines
3.6 KiB
HTML
<HTML
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><HEAD
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>Debugging</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
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TITLE="The Linux SCSI Generic (sg) HOWTO"
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TITLE="Programming example"
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>The Linux SCSI Generic (sg) HOWTO</TH
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CLASS="APPENDIX"
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><H1
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><A
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NAME="DEBUGGING">Appendix D. Debugging</H1
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><P
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>There are various ways to debug what is happening with the sg driver.
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The information provided in the <TT
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CLASS="FILENAME"
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>/proc/scsi/sg</TT
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>
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directory can be useful, especially the <TT
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CLASS="FILENAME"
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>debug</TT
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>
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pseudo file. It outputs the state of the sg driver when it is called.
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Invoking it at the right time can be a challenge. One approach (used in
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SANE) is to invoke the system() system call like this:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="PROGRAMLISTING"
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> system("cat /proc/scsi/sg/debug");</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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at appropriate times within an application that is using the sg driver.</P
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><P
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>Another debugging technique is to trace all system calls a program makes
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with the <B
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CLASS="COMMAND"
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>strace</B
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> command (see its "man" page). This
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command can also be used to obtain timing information (with the
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"-r" and "t" options).</P
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><P
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>To debug the sg driver itself then the kernel needs to be built with
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CONFIG_SCSI_LOGGING selected. Then copious output will be sent by the sg
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driver whenever it is invoked to the log (normally
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<TT
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CLASS="FILENAME"
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>/var/log/messages</TT
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>) and/or the console.
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This debug output is turned on by:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="PROGRAMLISTING"
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> $ echo "scsi log timeout 7" > /proc/scsi/scsi</PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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As the number (i.e. 7) is reduced, less output is generated. To turn off
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this type of debugging use:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="PROGRAMLISTING"
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> $ echo "scsi log timeout 0" > /proc/scsi/scsi</PRE
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></FONT
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></TD
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></TR
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></TABLE
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></P
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><P
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>If you want the system to log SCSI (CHECK_CONDITION related) errors that
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sg detects rather than process them within the application using sg
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then set ioctl(SG_SET_DEBUG) to a value greater than zero.
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Processing SCSI errors within the application using sg is my preference.</P
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></DIV
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>Programming example</TD
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><TD
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WIDTH="34%"
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> </TD
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WIDTH="33%"
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ALIGN="right"
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>Other references</TD
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> |