Re: [regression] CD-DA delay needed after insertion(http://bugzilla.kernel.org/show_bug.cgi?id=10974)

[James Bottomley]

On Mon, 2008-06-30 at 10:51 -0500, James Bottomley wrote:
> On Mon, 2008-06-30 at 11:25 +0200, Geert Uytterhoeven wrote:
> > 	Hi James,
> > 
> > On Fri, 27 Jun 2008, James Bottomley wrote:
> > > > git-bisect taught me it was introduced by
> > > > 
> > > > commit 38582a62ecd337de4212004c7d4844899dc57890
> > > > Author: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> > > > Date:   Wed Feb 6 13:01:58 2008 -0600
> > > > 
> > > >     [SCSI] sr: fix test unit ready responses
> > > >     
> > > >     Commit 210ba1d1724f5c4ed87a2ab1a21ca861a915f734 updated sr.c to use
> > > >     the scsi_test_unit_ready() function.  Unfortunately, this has the
> > > >     wrong characteristic of eating NOT_READY returns which sr.c relies on
> > > >     for tray status.
> > > >     
> > > >     Fix by rolling an internal sr_test_unit_ready() that doesn't do this.
> > > 
> > > OK, I thought I had a test case for this, but when I revert this commit
> > > on git head (and fix up the one reject which just leaves the sr_
> > > function in place) I still produce the same behaviour.
> > > 
> > > What I'm trying is 
> > > 
> > > sg_start -i -l <cdrom>
> > > 
> > > to close the tray followed by your cdparanoia command
> > > 
> > > Could you see if reverting this commit on git head works for you (in
> > > which case I'm not reproducing it correctly)?
> > 
> > On 9bedbcb207ed9a571b239231d99c8fd4a34ae24d, the sequence
> > 
> >     eject; sg_start -i -l /dev/scd0; cdparanoia \
> > 	-d /dev/scd0 -Z -q 1-1[:1] /dev/null || echo failed
> > 
> > fails with
> > 
> >     004: Unable to read table of contents header
> > 
> > After reverting 38582a62ecd337de4212004c7d4844899dc57890, it works.
> > 
> > I added the eject as the PS3 has a slot-loading drive.
> > 
> > With kind regards,
> 
> OK ... but this doesn't happen for me with or without this commit
> reverted.  This is what I see from stracing cdparanoia:
> 
> lstat64("/dev/scd0", {st_mode=S_IFBLK|0660, st_rdev=makedev(11, 0), ...}) = 0
> open("/dev/scd0", O_RDWR|O_NONBLOCK)    = 3
> ioctl(3, SG_IO, 0xbfc0afdc)             = -1 EINVAL (Invalid argument)
> close(3)                                = 0
> open("/dev/scd0", O_RDWR|O_NONBLOCK)    = 3
> dup(3)                                  = 4
> ioctl(3, CDROMAUDIOBUFSIZ or SCSI_IOCTL_GET_IDLUN, 0xbfc0b240) = 0
> ioctl(3, SCSI_IOCTL_GET_BUS_NUMBER, 0xbfc0b248) = 0
> ioctl(3, SG_IO, 0xbfc0af8c)             = 0
> ioctl(4, SG_EMULATED_HOST, 0xbfc0b2b8)  = 0
> ioctl(3, SG_IO, 0xbfc0b07c)             = 0
> ioctl(3, SG_IO, 0xbfc0b04c)             = 0
> write(2, "004: Unable to read table of con"..., 45004: Unable to read table of contents header) = 45
> 
> The O_NONBLOCK tells the cdrom layer not to do drive ready processing.
> 
> The three SG_IOs are INQUIRY, MODE_SENSE(10) and READ TOC/PMA/ATIP
> 
> The latter one is returned with a check condition and sense data not
> ready; medium not present - tray open.
> 
> There's no way the drive ready processing can have an effect on this
> sequence unless cdparanoia either invokes it from the cdrom layer or
> processes the not ready itself.  Could you strace your cdparanoia and
> see what sequence it is using?

OK ... I think I finally found the problem.  Our DVD drives obviously
have a slight difference in the way they handle tray close.  Mine still
returns tray open for a while after the close operation has been
initiated.  To see the behaviour you need it to return not ready; in
process of becoming ready.  The zero return from scsi_test_unit_ready()
actually causes sr_media_changed() incorrectly to return zero.  But,
before it does, it tries to update the CD information and capacity.
This is where the delay occurs ... as long as the drive reports in
process of becoming ready, sr_cd_check() will wait 2s and retry until it
becomes ready and it can get the CD information.

The problem is I don't think the new behaviour is a regression.
cdparanoia requested O_NONBLOCK ... it's a bit counter to this if we
wait for the drive to become ready.  cdparanoia doesn't care that we get
the correct CD parameters on the open since it's using SG_IO to
manipulate the device.  So, I think the bug is actually in cdparanoia.
If it requests O_NONBLOCK, it's asking for full status immediately and
is supposed to be able to cope with the returns (including knowing to
retry the NOT_READY ones).

James


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