linux-kernel - Re: [PATCH v2 1/3] usb: gadget: storage: Add fsg_get

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Message-ID: <Pine.LNX.4.44L0.1103211017240.1978-100000@iolanthe.rowland.org>
Date:	Mon, 21 Mar 2011 10:20:52 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roger Quadros <roger.quadros@...ia.com>
cc:	gregkh@...e.de, <sshtylyov@...sta.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] usb: gadget: storage: Add fsg_get_toc helper

On Mon, 21 Mar 2011, Roger Quadros wrote:

> From: Roger Quadros <roger.quadros@...ia.com>
> 
> 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@...ia.com>
> ---
>  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.

> +		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?

Alan Stern

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