[stgt] [PATCH] Make virtual tapes more closely emulate physical ones

[Jay Fenlason]

On Mon, Jan 14, 2013 at 09:02:34PM +0900, FUJITA Tomonori wrote:
> On Thu, 10 Jan 2013 11:36:44 -0500
> Jay Fenlason <fenlason at redhat.com> wrote:
> 
> > On my physical drive (a Sony AIT-2 drive, if it matters) when
> > userspace reads a file mark, it gets an EOF, and the tape is advanced
> > past the file mark so that a subsequent read will return data from the
> > next file on the tape.  With a virtual drive, the file mark is
> > sticky--reads continue to return EOF until the tape is manually
> > advanced with a FSF ioctl.  I wrote this quick patch to make the
> > virtual tape behave like my physical one.
> > 
> > I'm not sure about the sense_data_build hunk, but it matches the code
> > for fixed blocksize, and did no harm in my testing.
> > 
> > 		-- JF
> > 
> > --- tgt-1.0.32/usr/bs_ssc.c.filemark	2012-09-30 18:39:21.000000000 -0400
> > +++ tgt-1.0.32/usr/bs_ssc.c	2013-01-09 15:32:43.000000000 -0500
> > @@ -325,6 +325,9 @@
> >  		if (h->blk_type == BLK_EOD)
> >  			sense_data_build(cmd, 0x40 | BLANK_CHECK,
> >  					 NO_ADDITIONAL_SENSE);
> > +		else if (h->blk_type == BLK_FILEMARK)
> > +			ssc_sense_data_build(cmd, NO_SENSE | SENSE_FILEMARK,
> > +					     ASC_MARK, info, sizeof(info));
> >  		else
> >  			ssc_sense_data_build(cmd, NO_SENSE | 0x20,
> >  					     NO_ADDITIONAL_SENSE,
> > @@ -339,8 +342,13 @@
> >  
> >  		result = SAM_STAT_CHECK_CONDITION;
> >  
> > -		if (!length)
> > +		if (!length) {
> > +			if (h->blk_type == BLK_FILEMARK) {
> > +				ret = skip_next_header(cmd->dev);
> > +				/* FIXME: ??? */
> 
> Thanks, the patch looks correct. What's 'FIXME' part?

We're already reporting an error, and we just got another error (of
the "should never happen" variety).  What should we do?  It might be
that the only correct thing to do is silently ignore the error, in
which case the FIXME can be removed.  Mut if we should do something,
code to do it should go where the FIXME is.

			-- JF
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