On 10/18/2014 03:11 AM, Bart Van Assche wrote: > On 10/16/14 07:37, michaelc@xxxxxxxxxxx wrote: >> The following patches implement the SCSI command COMPARE_AND_WRITE as >> a new >> bio/request type REQ_CMP_AND_WRITE. COMPARE_AND_WRITE is defined in the >> SCSI SBC (SCSI block command) specs as: >> >> The COMPARE AND WRITE command requests that the device server perform the >> following as an uninterrupted series of actions: >> >> 1) perform the following operations: >> A) read the specified logical blocks; and >> B) transfer the specified number of logical blocks from the >> Data-Out >> Buffer (i.e., the verify instance of the data is transferred >> from the >> Data-Out Buffer); >> >> 2) compare the data read from the specified logical blocks with the >> verify >> instance of the data; and >> 3) If the compared data matches, then perform the following operations: >> 1) transfer the specified number of logical blocks from the >> Data-Out >> Buffer (i.e., the write instance of the data transferred from >> the >> Data-Out Buffer); and >> 2) write those logical blocks. > > Hello Mike, > > Just below the above text one can find the following additional > requirement in SBC-4: > <quote> > 4) if the compare operation does not indicate a match, then terminate > the command with CHECK CONDITION status with the sense key set to > MISCOMPARE and the additional sense code set to MISCOMPARE DURING > VERIFY OPERATION. In the sense data (see 4.18 and SPC-4) the offset > from the start of the Data-Out Buffer to the first byte of data that > was not equal shall be reported in the INFORMATION field. > </quote> > > What I'm wondering now is how requirement (4) can be supported if > REQ_CMP_AND_WRITE doesn't return the offset of the first byte that > didn't match ? Additionally, shouldn't compare_and_write_callback() be > fixed such that it returns the miscompare offset to its caller ? > Yeah, Hannes pointed out that the original LIO code did not support this. For the original code, I will fix that in another patchset to keep this one smaller and focused. For what I need, I have been trying to think of a nice way to pass additional info around. I think the options are: 1. Instead of making it bio/request based, make it a request_queue->compare_and_write function. We then just stack them and can add whatever arguments/return values are necessary and do not have to mess with the bio/request structs and function chains. 2. Add another argument to the end io functions that can be used to pass back bio/request type specific info. -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
