On 10/04/2017 06:40 AM, Daniel P. Berrange 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(+)
> bool tray_locked;
> + /*
> + * 0x0000 - rotation rate not reported
> + * 0x0001 - non-rotating medium (SSD)
> + * 0x0002-0x0400 - reserved
> + * 0x0401-0xffe - rotations per minute
s/0xffe/0xfffe/
> + * 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 */
This function is awkward - it is a non-local audit to see whether we are
at risk of overflowing any buffers due to the new output. But from
what I can see, I think you're safe.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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