On Tue, 2008-06-03 at 15:15 -0500, James Bottomley wrote: > On Tue, 2008-06-03 at 09:59 +0200, Arne Wiebalck wrote: > > Hi all, > > > > I got a problem using the SG_IO ioctl with our tape drives. > > In order to examine errors on our drives in more detail, I > > would like to make the sense bytes available to the > > application using the REQUEST_SENSE command. > > > > However, there's a discrepancy between the kernel output in > > /var/log/messages and what I see using SG_IO within my > > application: while the kernel sees > > > > kernel: st0: Error with sense data: scsi1 : destination target 0, lun 0 > > kernel: command = Space 01 00 0d d5 00 > > kernel: Info fld=0x1, Current st0: sense key Medium Error > > kernel: Additional sense: Read retries exhausted > > kernel: Raw sense data:0xf0 0x00 0x03 0x00 0x00 0x00 0x01 0x12 0x00 0x00 > > 0x00 0x00 0x11 0x01 0x00 0x00 0x00 0x00 0x37 0xf7 0x10 0x01 0x00 0x00 > > 0xf7 0x37 > > > > (which is realistic) the ioctl reports something like > > > > 70 00 00 00 00 00 00 12 00 00 00 00 00 00 00 00 > > 00 00 00 00 00 00 00 00 10 02 > > > > (since the first bit is not set, the sense bytes are not even valid, > > as far as I understand). > > > > So, could it be that the sense bytes are already cleared when I request > > them? They cleared/set by the next SCSI cmd, I assume? But shouldn't > > they be valid even then? > > > > I also tried the sg3-utils to query the drive's sense bytes, and they > > report (almost) the same sense bytes as SG_IO inside my application > > does. Sending an INQUIRY cmd using sg3_utils works fine, btw. > > > > Maybe that's all a plain usage error, so please find the code I use > > below. > > > > Anything obvious I am doing wrong here? All comments appreciated. > > Yes: SCSI automatically requests sense in response to a check condition. > So, the sense should be attached to the SG_IO command that receives the > error. You can't do an additional request sense for it because the > sense has already been cleared by the automatic request sense the > mid-layer did. > > Does the sense data really not get returned by the SG_IO command that > actually encounters the check condition return? The code does not use SG_IO interface until now. The command that encounters the error is a read or a write. Is there a way to get the sense bytes in such a case (except for replacing all read/write calls with the corresponding SG_IO commands)? TIA, Arne -- 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
