On Sat, 1 Feb 2014, Steph Nguyen wrote: > Hi > > It seems that when sending SCSI commands over USB, the kernel doesn't > necessary build a sense response. For instance, when sending REQUEST > SENSE over ehci, the scsi_cmnd->sense_buffer is left NULL; if I run the > same REQUEST SENSE command over a direct SCSI connect, the kernel builds > the scsi_cmnd->sense_buffer.
There's no need for the kernel to build a sense buffer when sending a REQUEST SENSE command. That command always succeeds, so there's no reason to ask for sense data which might explain why the command failed. Your question isn't very precise. How did you "run" a REQUEST SENSE command? When using usb-storage under normal conditions, the SCSI layer doesn't ever send that command. > So is there a reason why usb-storage doesn't build the sense buffer? In general, usb-storage doesn't touch scsi_cmnd except to set scsi_cmnd->result. (There are a few exceptions, but this is mostly true.) If the SCSI layer wants to receive sense data, it has to set the scsi_cmnd->sense_buffer field itself. Normally it does so. For example, see what happens when the SCSI layer issues a TEST UNIT READY command to usb-storage. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
