On Wed, Oct 04, 2017 at 05:49:44PM +0100, Dr. David Alan Gilbert wrote:
> * Daniel P. Berrange (berra...@redhat.com) wrote:
> > The Linux kernel will query the SCSI "Block device characteristics"
> > VPD to determine the rotations per minute of the disk. If this has
> > the value 1, it is taken to be an SSD and so Linux sets the
> > 'rotational' flag to 0 for the I/O queue and will stop using that
> > disk as a source of random entropy. Other operating systems may
> > also take into account rotation rate when setting up default
> > behaviour.
> >
> > Mgmt apps should be able to set the rotation rate for virtualized
> > block devices, based on characteristics of the host storage in use,
> > so that the guest OS gets sensible behaviour out of the box. This
> > patch thus adds a 'rotation-rate' parameter for 'scsi-hd' and
> > 'scsi-block' device types. For the latter, this parameter will be
> > ignored unless the host device has TYPE_DISK.
> >
> > Signed-off-by: Daniel P. Berrange <berra...@redhat.com>
> > ---
> > hw/scsi/scsi-disk.c | 20 ++++++++++++++++++++
> > 1 file changed, 20 insertions(+)
> >
> > diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
> > index 6e841fb5ff..a518080e7d 100644
> > --- a/hw/scsi/scsi-disk.c
> > +++ b/hw/scsi/scsi-disk.c
> > @@ -104,6 +104,14 @@ typedef struct SCSIDiskState
> > char *product;
> > bool tray_open;
> > bool tray_locked;
> > + /*
> > + * 0x0000 - rotation rate not reported
> > + * 0x0001 - non-rotating medium (SSD)
> > + * 0x0002-0x0400 - reserved
> > + * 0x0401-0xffe - rotations per minute
> > + * 0xffff - reserved
> > + */
> > + uint16_t rotation_rate;
> > } SCSIDiskState;
> >
> > static bool scsi_handle_rw_error(SCSIDiskReq *r, int error, bool
> > acct_failed);
> > @@ -605,6 +613,7 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req,
> > uint8_t *outbuf)
> > outbuf[buflen++] = 0x83; // device identification
> > if (s->qdev.type == TYPE_DISK) {
> > outbuf[buflen++] = 0xb0; // block limits
> > + outbuf[buflen++] = 0xb1; /* block device characteristics */
> > outbuf[buflen++] = 0xb2; // thin provisioning
> > }
> > break;
> > @@ -747,6 +756,15 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req,
> > uint8_t *outbuf)
> > outbuf[43] = max_io_sectors & 0xff;
> > break;
> > }
> > + case 0xb1: /* block device characteristics */
> > + {
> > + buflen = 8;
> > + outbuf[4] = (s->rotation_rate >> 8) & 0xff;
> > + outbuf[5] = s->rotation_rate & 0xff;
> > + outbuf[6] = 0;
> > + outbuf[7] = 0;
> > + break;
> > + }
> > case 0xb2: /* thin provisioning */
> > {
> > buflen = 8;
> > @@ -2911,6 +2929,7 @@ static Property scsi_hd_properties[] = {
> > DEFAULT_MAX_UNMAP_SIZE),
> > DEFINE_PROP_UINT64("max_io_size", SCSIDiskState, max_io_size,
> > DEFAULT_MAX_IO_SIZE),
> > + DEFINE_PROP_UINT16("rotation_rate", SCSIDiskState, rotation_rate, 0),
> > DEFINE_BLOCK_CHS_PROPERTIES(SCSIDiskState, qdev.conf),
> > DEFINE_PROP_END_OF_LIST(),
> > };
> > @@ -2982,6 +3001,7 @@ static const TypeInfo scsi_cd_info = {
> > static Property scsi_block_properties[] = {
> > DEFINE_BLOCK_ERROR_PROPERTIES(SCSIDiskState, qdev.conf), \
> > DEFINE_PROP_DRIVE("drive", SCSIDiskState, qdev.conf.blk),
> > + DEFINE_PROP_UINT16("rotation_rate", SCSIDiskState, rotation_rate, 0),
> > DEFINE_PROP_END_OF_LIST(),
> > };
>
> Are you sure you want this as a property of SCSIDiskState etc rather
> than a property on the underlying drive?
> Then if virtio devices etc wanted to pick this up later they could
> without needing extra parameters.
That would make 'rotation_rate' available for everything, regardless
of whether its used/supported by the frontend device. I was trying to
restrict this to only the places where its appropriate, so only disks,
not cdroms for example.
Regards,
Daniel
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