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

[FUJITA Tomonori]

On Mon, 14 Jan 2013 12:53:32 -0500
Jay Fenlason <fenlason at redhat.com> wrote:

> 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.

Thanks, I see. If you send an updated patch including the above
description instead of 'FIXME', I'll apply it.

Looks like that the length checking could be done earlier.
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