Re: [PATCH] usb: gadget: storage: add support for media larger than 2T

[Alan Stern <stern@rowland.harvard.edu>]

On Tue, Sep 14, 2021 at 08:27:28AM +0300, Nikita Yushchenko wrote:
> This adds support for READ_CAPACITY(16), READ(16) and WRITE(16)
> commands, and fixes READ_CAPACITY command to return 0xffffffff if
> media size does not fit in 32 bits.
> 
> This makes f_mass_storage to export a 16T disk array correctly.
> 
> Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
> ---
>  drivers/usb/gadget/function/f_mass_storage.c | 70 ++++++++++++++++++--
>  1 file changed, 63 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
> index 7c96c4665178..b79737c19750 100644
> --- a/drivers/usb/gadget/function/f_mass_storage.c
> +++ b/drivers/usb/gadget/function/f_mass_storage.c
> @@ -619,7 +619,7 @@ static int sleep_thread(struct fsg_common *common, bool can_freeze,
>  static int do_read(struct fsg_common *common)
>  {
>  	struct fsg_lun		*curlun = common->curlun;
> -	u32			lba;
> +	u64			lba;
>  	struct fsg_buffhd	*bh;
>  	int			rc;
>  	u32			amount_left;
> @@ -634,7 +634,10 @@ static int do_read(struct fsg_common *common)
>  	if (common->cmnd[0] == READ_6)
>  		lba = get_unaligned_be24(&common->cmnd[1]);
>  	else {
> -		lba = get_unaligned_be32(&common->cmnd[2]);
> +		if (common->cmnd[0] == READ_16)
> +			lba = get_unaligned_be64(&common->cmnd[2]);
> +		else

It would be good to put a comment here:

		else	/* READ_10 or READ_12 */

Same for the WRITE_10/WRITE_12 case below.

> +			lba = get_unaligned_be32(&common->cmnd[2]);
>  
>  		/*
>  		 * We allow DPO (Disable Page Out = don't save data in the
> @@ -747,7 +750,7 @@ static int do_read(struct fsg_common *common)
>  static int do_write(struct fsg_common *common)
>  {
>  	struct fsg_lun		*curlun = common->curlun;
> -	u32			lba;
> +	u64			lba;
>  	struct fsg_buffhd	*bh;
>  	int			get_some_more;
>  	u32			amount_left_to_req, amount_left_to_write;
> @@ -771,7 +774,10 @@ static int do_write(struct fsg_common *common)
>  	if (common->cmnd[0] == WRITE_6)
>  		lba = get_unaligned_be24(&common->cmnd[1]);
>  	else {
> -		lba = get_unaligned_be32(&common->cmnd[2]);
> +		if (common->cmnd[0] == WRITE_16)
> +			lba = get_unaligned_be64(&common->cmnd[2]);
> +		else
> +			lba = get_unaligned_be32(&common->cmnd[2]);
>  
>  		/*
>  		 * We allow DPO (Disable Page Out = don't save data in the
> @@ -1146,6 +1152,7 @@ static int do_read_capacity(struct fsg_common *common, struct fsg_buffhd *bh)
>  	u32		lba = get_unaligned_be32(&common->cmnd[2]);
>  	int		pmi = common->cmnd[8];
>  	u8		*buf = (u8 *)bh->buf;
> +	u32		mlb;

The Linux kernel does not suffer from a shortage of letters; you don't 
have to struggle to conserve them.  This variable should be named 
max_lba or something similar.  (Note: To readers in the US, "mlb" stands 
for "Major League Baseball"!)

>  
>  	/* Check the PMI and LBA fields */
>  	if (pmi > 1 || (pmi == 0 && lba != 0)) {
> @@ -1153,12 +1160,28 @@ static int do_read_capacity(struct fsg_common *common, struct fsg_buffhd *bh)
>  		return -EINVAL;
>  	}
>  
> -	put_unaligned_be32(curlun->num_sectors - 1, &buf[0]);
> -						/* Max logical block */
> -	put_unaligned_be32(curlun->blksize, &buf[4]);/* Block length */
> +	if (curlun->num_sectors < 0x100000000ULL)
> +		mlb = curlun->num_sectors - 1;
> +	else
> +		mlb = 0xffffffff;
> +	put_unaligned_be32(mlb, &buf[0]);		/* Max logical block */
> +	put_unaligned_be32(curlun->blksize, &buf[4]);	/* Block length */
>  	return 8;
>  }
>  
> +static int do_read_capacity_16(struct fsg_common *common, struct fsg_buffhd *bh)
> +{
> +	struct fsg_lun  *curlun = common->curlun;
> +	u8		*buf = (u8 *)bh->buf;
> +
> +	put_unaligned_be64(curlun->num_sectors - 1, &buf[0]);
> +							/* Max logical block */
> +	put_unaligned_be32(curlun->blksize, &buf[8]);	/* Block length */
> +	/* It is safe to keep other fields zeroed */

Blank line preceding the comment, please.

> +	memset(&buf[12], 0, 32 - 12);
> +	return 32;
> +}
> +
>  static int do_read_header(struct fsg_common *common, struct fsg_buffhd *bh)
>  {
>  	struct fsg_lun	*curlun = common->curlun;
> @@ -1905,6 +1928,17 @@ static int do_scsi_command(struct fsg_common *common)
>  			reply = do_read(common);
>  		break;
>  
> +	case READ_16:
> +		common->data_size_from_cmnd =
> +				get_unaligned_be32(&common->cmnd[10]);
> +		reply = check_command_size_in_blocks(common, 16,
> +				      DATA_DIR_TO_HOST,
> +				      (1<<1) | (0xff<<2) | (0xf<<10), 1,
> +				      "READ(16)");
> +		if (reply == 0)
> +			reply = do_read(common);
> +		break;
> +
>  	case READ_CAPACITY:
>  		common->data_size_from_cmnd = 8;
>  		reply = check_command(common, 10, DATA_DIR_TO_HOST,
> @@ -1914,6 +1948,17 @@ static int do_scsi_command(struct fsg_common *common)
>  			reply = do_read_capacity(common, bh);
>  		break;
>  
> +	case SERVICE_ACTION_IN_16:

I realize that this is the code for READ_CAPACITY_16, but the commands 
should be kept in alphabetical order by symbol name.  So this belongs 
lower down, after REQUEST_SENSE.

> +		if ((common->cmnd[1] & 0x1f) != SAI_READ_CAPACITY_16)
> +			goto unknown_cmnd;
> +		common->data_size_from_cmnd = 32;

This should be get_unaligned_be32(&common->cmnd[10]).

> +		reply = check_command(common, 14, DATA_DIR_TO_HOST,

16, not 14.

> +				      (1<<1) | (1<<13), 1,

Do you want to disallow nonzero values for the LBA field?  Then
this should be (1<<1) | (0xf<<10) | (1<<14).  If you also want to 
disallow nonzero values for the PMI bit, omit the (1<<14) part.

> +				      "READ CAPACITY(16)");
> +		if (reply == 0)
> +			reply = do_read_capacity_16(common, bh);
> +		break;
> +
>  	case READ_HEADER:
>  		if (!common->curlun || !common->curlun->cdrom)
>  			goto unknown_cmnd;
> @@ -2028,6 +2073,17 @@ static int do_scsi_command(struct fsg_common *common)
>  			reply = do_write(common);
>  		break;
>  
> +	case WRITE_16:
> +		common->data_size_from_cmnd =
> +				get_unaligned_be32(&common->cmnd[10]);
> +		reply = check_command_size_in_blocks(common, 16,
> +				      DATA_DIR_FROM_HOST,
> +				      (1<<1) | (0xff<<2) | (0xf<<10), 1,
> +				      "WRITE(16)");
> +		if (reply == 0)
> +			reply = do_write(common);
> +		break;
> +
>  	/*
>  	 * Some mandatory commands that we recognize but don't implement.
>  	 * They don't mean much in this setting.  It's left as an exercise

Please resubmit the patch with these changes.

Alan Stern