RE: [Qemu-devel] [PATCH] scsi disk block descriptor

[Krumme, Chris]

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> rg] On Behalf Of Artyom Tarasenko
> Sent: Tuesday, October 13, 2009 3:20 PM
> To: qemu-devel; Blue Swirl
> Subject: [Qemu-devel] [PATCH] scsi disk block descriptor
> 
> The SCSI-2 documentation suggests, that although the block
> descriptor is optional for an arbitrary SCSI-2 device (chapter 8.2.10,
> http://ldkelley.com/SCSI2/SCSI2/SCSI2/SCSI2/SCSI2-08.html )
> it is mandatory for a disk: chapters 9.1.2, 9.3.3
> ( http://ldkelley.com/SCSI2/SCSI2/SCSI2/SCSI2-09.html ) don't say
> "optional" any more, just "The block descriptor in the MODE SENSE
> data describes the block lengths that are used on the medium."
> 
> Signed-off-by: Artyom Tarasenko <address@hidden>
> ---
> diff --git a/hw/scsi-disk.c b/hw/scsi-disk.c
> index 3940726..b703379 100644
> --- a/hw/scsi-disk.c
> +++ b/hw/scsi-disk.c
> @@ -624,7 +624,9 @@ static int32_t scsi_send_command(SCSIDevice *d,
> uint32_t tag,
>          {
>              uint8_t *p;
>              int page;
> -
> +            int dbd;
> +
> +            dbd = buf[1]  & 0x8;
>              page = buf[2] & 0x3f;
>              DPRINTF("Mode Sense (page %d, len %d)\n", page, len);
>              p = outbuf;
> @@ -635,6 +637,24 @@ static int32_t scsi_send_command(SCSIDevice *d,
> uint32_t tag,
>                  outbuf[2] = 0x80; /* Readonly.  */
>              }
>              p += 4;
> +            bdrv_get_geometry(s->dinfo->bdrv, &nb_sectors);
> +            if ((~dbd) & nb_sectors) {
> +                nb_sectors /= s->cluster_size;
> +                if (nb_sectors > UINT32_MAX)
> +                    nb_sectors = UINT32_MAX;
> +                nb_sectors--;
> +                outbuf[3] = 8; /* Block descriptor length  */
> +                p[0] = 0; /* media density code */
> +                p[1] = (nb_sectors >> 16) & 0xff;
> +                p[2] = (nb_sectors >> 8) & 0xff;
> +                p[3] = nb_sectors & 0xff;

Hello Artyom,

Above you limit to 32 bits - 1, then you use the bottom 24 bits.  Would
it be better to limit to 24 bits - 1, then a drive with more than 24
bits of sectors will show as maximum size rather than a random size?

Thanks

Chris

> +                p[4] = 0; /* reserved */
> +                p[5] = 0; /* bytes 5-7 are the sector size 
> in bytes */
> +                p[6] = s->cluster_size * 2;
> +                p[7] = 0;
> +                p += 8;
> +            }
> +
>              if (page == 4) {
>                  int cylinders, heads, secs;
>