On Mon, 2014-01-13 at 11:27 -0800, Nicholas A. Bellinger wrote: > On Mon, 2014-01-13 at 10:52 -0800, James Bottomley wrote: > > On Mon, 2014-01-13 at 10:30 -0800, Nicholas A. Bellinger wrote: > > > Hey MKP, > > > > > > On Fri, 2014-01-10 at 16:01 -0500, Martin K. Petersen wrote: > > > > >>>>> "nab" == Nicholas A Bellinger <nab@xxxxxxxxxxxxx> writes: > > > > > > > > nab> This patch adds support for exposing DIF protection device > > > > nab> attributes via configfs. This includes: > > > > > > > > nab> pi_prot_type: Protection Type (0, 1, 3 currently support) > > > > nab> pi_prot_version: Protection Version (DIF v1 currently supported) > > > > > > > > What's DIF v2? > > > > > > > > > > This would be the proposed 16-byte protection scheme for SBC4. > > > > What proposed 16 byte scheme? The only DIF proposals I know for SBC-4 > > are 13-185R0 and 12-369R0 and that's a couple of new algorithms and > > types because we cannot change the 8 byte PI. > > > > Then I'm probably getting the SBC version wrong.. It's the one that > includes using CRC32C for the block guard, and larger space for > reference tag as mentioned by MKP. Well, this isn't reducing my confusion: I think you're referring to 12-369r0 which proposes to *eliminate* the reference tag (by moving it into the CRC calculation) and use the recovered 4 bytes to expand the CRC to CRC32 and add two bytes to the application tag, so they both become 4 bytes long, but the new PI still occupies only 8 bytes on disk. Perhaps it's also better to clarify the terminology: The PI is composed of a Guard field, which is the checksum, an application tag, which is usable by the application for anything it wants and a reference tag which is designed to be derived from the on-disk location so it can be used to detect misplaced writes. In Type 1 the reference tag has to be the lower 31 bits of the LBA and in type 3 it's application defined. In all current types, the guard is two bytes and the application tag two bytes. James -- 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
