On Wed, 12 May 2010, Mark Lord wrote: > The sticky part is that hdparm explicitly asked for sense data. > > But the results were marked as "no sense data". Many of the commands > sent by hdparm _require_ "sense data" (ATA register values) in order > to see the results. The USB driver appears to ignore that request > when it sees good device status from the original command. Bug. This sounds like it is a bug in the SCSI midlayer, not in usb-storage. There is no mechanism for the midlayer to tell low-level drivers like usb-storage that sense data must be returned. The documentation in include/scsi/scsi_cmnd.h merely states that the sense buffer should be filled when CHECK CONDITION is received for the original command. Ditto for Documentation/scsi/scsi_mid_low_api.txt. Hence if sense data is needed even in the absence of CHECK CONDITION, the midlayer must explicitly send a command to retrieve it. What mechanism does hdparm use to submit its I/O requests, and how does it indicate that it requires sense data? Alan Stern -- 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
