On Fri, 2013-09-13 at 13:58 +0100, Andy Whitcroft wrote: > tl;dr -- enable TRIM support for Hyper-V emulated disks. > > The Hyper-V hypervisor can support TRIM for its devices, advertising this > via the appropriate VPD pages. However the emulated disks only claim > to be SPC-2 devices. According to the specs VPD pages (in general) did > exist at SPC-2 but the specific pages we interogate for the TRIM support > did not until SPC-3 therefore the kernel avoids reading the relevant pages > for SPC-2 devices and prevents TRIM from being offered for these devices. > Additionally at SPC-2 we prefer ReadCapacity10 over ReadCapacity16 and > unless we use RC16 we will not identify the device as TRIM capable also > preventing TRIM being offered. > > As the VPD page zero does list which pages are valid for each device, it > could be argued that we could simply attempt to use these pages for all > devices which claim to be SPC-2 and above. While this seems valid the > code documents a number of devices which take badly to having even VPD > page 0 interogated even when supposedly supported. Therefore it seems > appropriate to add a scsi device flag to allow a device to request SPC-3 > VPD pages be used when only at SPC-2. > > Similarly for the ReadCapacity selection it seems dangerous to invert > the order for all SPC-2 devices. So it seems appropriate to add a scsi > device flag to request we try RC16 before RC10 (mirroring the existing > flag for the opposite). > > The following four patches add the two scsi device flags and select those > flags for the Hyper-V emulated disks. > > Patches against v3.11. > > Comments? This is an awful lot of contortions (which don't seem to have any other users on the horizon) to support a device that's not standards compliant. What about this, it's simple, it does the right thing and it's contained in the driver of the problem device. James --- diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c index 83ec1aa..bd86a4b 100644 --- a/drivers/scsi/storvsc_drv.c +++ b/drivers/scsi/storvsc_drv.c @@ -1438,6 +1438,12 @@ static int storvsc_device_configure(struct scsi_device *sdevice) sdevice->no_write_same = 1; + /* + * hyper-v is stupid and lies about its capabilities + * If we pretend to be SPC-3, we send RC16 which activates trim + */ + sdevice->scsi_level = SCSI_SPC_3; + return 0; } -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
