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<TITLE>sane-devel: Re: reaction to a smaller buffer size</TITLE>
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<META NAME="Author" CONTENT="Oliver Neukum (Oliver.Neukum@lrz.uni-muenchen.de)">
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<META NAME="Subject" CONTENT="Re: reaction to a smaller buffer size">
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<H1>Re: reaction to a smaller buffer size</H1>
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<!-- received="Sun Nov 19 09:52:25 2000" -->
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<!-- name="Oliver Neukum" -->
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<STRONG>From:</STRONG> Oliver Neukum (<A HREF="mailto:Oliver.Neukum@lrz.uni-muenchen.de?Subject=Re:%20reaction%20to%20a%20smaller%20buffer%20size&In-Reply-To=<00111919071000.00396@ghanima>"><EM>Oliver.Neukum@lrz.uni-muenchen.de</EM></A>)<BR>
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<STRONG>Date:</STRONG> Sun Nov 19 2000 - 10:07:10 PST
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<EM>> The problem is that a backend may consider sanei_scsi_max_request_size
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</EM><BR>
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<EM>> as a constant. This was true for the old Linux SG driver; but with the
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</EM><BR>
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<EM>> new SG driver it is at least in theory possible that you get different
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</EM><BR>
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<EM>> buffer sizes each time a SG device file is opened. (Not very likely, but
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</EM><BR>
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<EM>> it is possible)
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</EM><BR>
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<P>It's virtually certain if you have two host adapters, whose drivers differ
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<BR>
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in their ability to do scatter/gather. This means that SANE will always
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<BR>
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fail in that setup.
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<BR>
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<P><EM>> Both situations might have caused unnecessary work and headaches for
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</EM><BR>
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<EM>> backend developers, who don't need or don't want to switch to
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</EM><BR>
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<EM>> sanei_scsi_open_extended, and therefore I decided to use this "paranoid"
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</EM><BR>
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<EM>> looking "if (real_buffersize != wanted_buffersize)", when I introduced
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</EM><BR>
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<EM>> sane_scsi_open_extended and related stuff.
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</EM><BR>
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<P>I see, but in the case I mentioned above the user needs to limit the
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<BR>
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buffer by setting enviromental variables.
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<BR>
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<P><EM>> > Why don't you use sanei_scsi_open_extended if it is available for your
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</EM><BR>
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<EM>> > paltform? In this case the backend can try to get a big buffer and
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</EM><BR>
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<EM>> > knows the actual size it is allowed to use.
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</EM><BR>
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<P>I am using an existing backend (microtek2). It works with this check removed.
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<BR>
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Is converting a backend to use sanei_scsi_open_extended difficult ?
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<BR>
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<P> Regards
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<BR>
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Oliver
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<BR>
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<P><PRE>
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--
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Source code, list archive, and docs: <A HREF="http://www.mostang.com/sane/">http://www.mostang.com/sane/</A>
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<EM>
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This archive was generated by <A HREF="http://www.hypermail.org/">hypermail 2b29</A>
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: <EM>Sun Nov 19 2000 - 09:52:39 PST</EM>
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