> -----Original Message----- > From: linux-scsi-ow...@vger.kernel.org [mailto:linux-scsi- > ow...@vger.kernel.org] On Behalf Of Douglas Gilbert > Sent: Thursday, 16 October, 2014 3:02 PM ... > On 14-10-16 12:39 PM, Douglas Gilbert wrote: ... > > The COMPARE AND WRITE command may fail for other reasons > > such as a transport problem or a Unit Attention, so the > > SCSI eh logic may need to know about it. > > Elaborating ... > > Hannes will enjoy this one: say a COMPARE AND WRITE (CAW) fails > due to a transport error or timeout. What should the EH do *** ? > Answer: read that LBA(s) to see whether the command succeeded > (i.e. wrote the new data)! If it did, do nothing; if it didn't, > repeat the CAW command. And naturally that second CAW may > yield a MISCOMPARE.
I don't think that is safe.. detecting the write data is in place doesn't prove the COMPARE AND WRITE really worked as a whole. Example: if two applications do this: * application 1: COMPARE AND WRITE: change 4 to 6 * application 2: COMPARE AND WRITE: change 5 to 6 and they both run into transport errors, then they'll both read back 6 and think their commands worked when really only one of them worked. --- Rob Elliott HP Server Storage -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
