Re: [PATCH v2 1/3] usb: gadget: storage: Add fsg_get_toc helper

[Roger Quadros]

On 03/21/2011 04:20 PM, ext Alan Stern wrote:
> On Mon, 21 Mar 2011, Roger Quadros wrote:
>
> > From: Roger Quadros<roger.quadros@xxxxxxxxx>
> >
> > fsg_get_toc can be used by both storage gadgets to build a CD-ROM
> > Table of Contents which can be used as data for READ_TOC command.
> > Currently fsg_get_toc supports two TOC formats, i.e.
> > format 0: Formatted TOC and format 2: Raw TOC.
> >
> > Raw TOC is required for CD-ROM emulation to work with Mac OS-X.
> >
> > Signed-off-by: Roger Quadros<roger.quadros@xxxxxxxxx>
> > ---
> >   drivers/usb/gadget/storage_common.c |   68 +++++++++++++++++++++++++++++++++++
> >   1 files changed, 68 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c
> > index b015561..d47f148 100644
> > --- a/drivers/usb/gadget/storage_common.c
> > +++ b/drivers/usb/gadget/storage_common.c
> > @@ -655,6 +655,74 @@ static void store_cdrom_address(u8 *dest, int msf, u32 addr)
> >   	}
> >   }
> >
> > +/**
> > + * fsg_get_toc() - Builds a TOC with required format @format.
> > + * @curlun: The LUN for which the TOC has to be built
> > + * @msf: Min Sec Frame format or LBA format for address
> > + * @format: TOC format code
> > + * @buf: The buffer into which the TOC is built
> > + *
> > + * Builds a Table of Content which can be used as data for READ_TOC command.
> > + * The TOC simulates a single session, single track CD-ROM mode 1 disc.
> > + *
> > + * Returns number of bytes written to @buf, -EINVAL if format not supported.
> > + */
> > +static int fsg_get_toc(struct fsg_lun *curlun, int msf, int format, u8 *buf)
> > +{
> > +	int i, len;
> > +	switch (format) {
> > +	case 0:
> > +		/* Formatted TOC */
> > +		len = 4 + 2*8;		/* 4 byte header + 2 descriptors */
> > +		memset(buf, 0, len);
> > +		len -= 2;		/* TOC Length excludes length field */
> > +		buf[1] = len;		/* TOC data length */
>
> These two lines are wrong.  You should do:
>
> 		buf[1] = len - 2;	/* TOC data length excludes header */
>
> The way it is now, the function ends up returning 18 instead of 20,
> causing the wrong amount of data to be transmitted.

Yes indeed.

> > +		buf[2] = 1;		/* First track number */
> > +		buf[3] = 1;		/* Last track number */
> > +		buf[5] = 0x16;		/* Data track, copying allowed */
> > +		buf[6] = 0x01;		/* Only track is number 1 */
> > +		store_cdrom_address(&buf[8], msf, 0);
> > +
> > +		buf[13] = 0x16;		/* Lead-out track is data */
> > +		buf[14] = 0xAA;		/* Lead-out track number */
> > +		store_cdrom_address(&buf[16], msf, curlun->num_sectors);
> > +		return len;
> > +		break;
> > +
> > +	case 2:
> > +		/* Raw TOC */
> > +		len = 4 + 3*11;		/* 4 byte header + 3 descriptors */
> > +		memset(buf, 0, len);	/* Header + A0, A1&  A2 descriptors */
> > +		len -= 2;		/* TOC Length excludes length field */
> > +		buf[1] = len;		/* TOC data length */
>
> Same thing here.  I'm surprised it worked during testing.  Did you
> really check to see that the correct data was being sent?

I too am surprised. I tried playing a few videos without problems.
After you pointed out the problem I ran a checksum on the files and they match!!

But thanks for pointing out, I'll send a new patch.

--
regards,
-roger
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