Re: [PATCH v3 02/18] block: introduce BLK_STS_DURATION_LIMIT

[Bart Van Assche <bvanassche@acm.org>]

On 1/24/23 11:59, Keith Busch wrote:
> On Tue, Jan 24, 2023 at 11:29:10AM -0800, Bart Van Assche wrote:
>> On 1/24/23 11:02, Niklas Cassel wrote:
>>> Introduce the new block IO status BLK_STS_DURATION_LIMIT for LLDDs to
>>> report command that failed due to a command duration limit being
>>> exceeded. This new status is mapped to the ETIME error code to allow
>>> users to differentiate "soft" duration limit failures from other more
>>> serious hardware related errors.
>>
>> What makes exceeding the duration limit different from an I/O timeout
>> (BLK_STS_TIMEOUT)? Why is it important to tell the difference between an I/O
>> timeout and exceeding the command duration limit?
> 
> BLK_STS_TIMEOUT should be used if the target device doesn't provide any
> response to the command. The DURATION_LIMIT status is used when the device
> completes a command with that status.

Hi Keith,

 From SPC-6: "The MAX ACTIVE TIME field specifies an upper limit on the 
time that elapses from the time at which the device server initiates 
actions to access, transfer, or act upon the specified data until the 
time the device server returns status for the command."

My interpretation of the above text is that the SCSI command duration 
limit specifies a hard limit, the same type of limit reported by the 
status code BLK_STS_TIMEOUT. It is not clear to me from the patch 
description why a new status code is needed for reporting that the 
command duration limit has been exceeded.

Thanks,

Bart.