On Nov 09 Elliott, Robert (Server Storage) wrote: > I recommend broadening this patch. T10 is discussing making READ (10), WRITE > (10), etc. obsolete in SBC-4 in favor of their 16-byte CDB counterparts. > > The algorithm should be: > 1. During discovery, determine if 16-byte CDBs are supported. There are > several ways to determine this: > a) REPORT SUPPORTED OPERATION CODES command succeeds and reports that READ > (16) et al are supported. > b) READ (16) command specifying a Transfer Length of zero succeeds. > c) READ CAPACITY (16) command succeeds and reports that the capacity is > 2 > TiB. > d) (future) INQUIRY command succeeds fetching the Block Device > Characteristics VPD page and notices a new field added by the SBC-4 > simplified SCSI feature set proposal. > > Since REPORT SUPPORTED OPERATION CODES is optional, it won't always work. > READ CAPACITY (16) used to be optional for < 2 TiB drives, so it won't always > work either. READ (16) will always work, but requires the drive to be spun up > beforehand (e.g., with START STOP UNIT).
This won't work. It will crash badly written device firmwares. Instead, try the (10) commands on the SBC-4 device and let it respond that it does not implement these commands. Or have other means to be certain of SBC-4 compliance without issuing commands that were optional in or not defined by earlier revisions of the spec. I wonder whether testing for INQUIRY_data.VERSION >= something is a sufficiently safe test. > 2. if 16-byte CDBs are supported, then use them; only drop down to 10-byte > CDBs if 16-byte CDBs are unavailable. Don't make the decision by comparing > the LBA on every IO. -- Stefan Richter -=====-===-- =-== -=-== http://arcgraph.de/sr/ -- 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
