Re: [PATCH v3 1/2] scsi: Handle Unit Attention when issuing SCSI command

[Bart Van Assche <Bart.VanAssche@sandisk.com>]

On Wed, 2016-10-26 at 08:52 -0700, James Bottomley wrote:
> On Wed, 2016-10-26 at 08:42 -0700, Bart Van Assche wrote:
> > Can you elaborate on this? Since the sense buffer is available in 
> > scsi_io_completion() and since that function already calls 
> > scsi_command_normalize_sense() this function seems like a good 
> > candidate to me to add retry logic for REQ_TYPE_BLOCK_PC requests.
> 
> UAs are used to signal AENs to userspace control processes that use
> BLOCK_PC, like CD changers, burners and scanners.  If we eat UAs
> inside scsi_io_completion(), we could potentially break any userspace
> control system that relies on AENs.

Ignoring the SCSI error handler, the call sequence for reporting UAs to
user space is as follows: scsi_softirq_done() ->
scsi_decide_disposition() -> scsi_check_sense() -> scsi_report_sense().
This means that scsi_report_sense() is called before
scsi_io_completion() is called. I think this means that what
scsi_io_completion() decides cannot affect UA reporting to user space?

Bart.