Re: [Scst-devel] scst aen how to send and catch?

[Bart V. A. <Bar...@wd...>]

On Sat, 2017-08-05 at 09:55 +0300, Vasiliy Tolstov wrote:
> =)) So as i see AEN not sended and only UA. Because i can't see
> "Capacity data has changed" messages without touching exported device
> on initiator. Can you give me some reasons why aen not supported?
> My scst.conf:
> HANDLER vdisk_fileio {
>         DEVICE sds01 {
>                 filename /dev/md127
>                 nv_cache 1
>                 rotational 0
>         }
> }
> 
> TARGET_DRIVER ib_srpt {
>         TARGET fe80:0000:0000:0000:0002:c903:0009:2bc5 {
>                 enabled 1
>                 io_grouping_type this_group_only
>                 rel_tgt_id 1
> 
>                 LUN 0 sds01
>         }
>         TARGET fe80:0000:0000:0000:0002:c903:0009:2bc6 {
>                 enabled 1
>                 io_grouping_type this_group_only
>                 rel_tgt_id 2
> 
>                 LUN 0 sds01
>         }
> }

Hello Vasiliy,

Several years ago I experimented with adding AEN support to both the ib_srpt
and ib_srp kernel drivers. However, while testing these changes I noticed
that if ib_srpt sends an AEN (called SRP_AER_REQ in the SRP protocol spec)
that this crashes any connected Windows SRP initiator systems. Although this
is cleary a bug in the Windows SRP initiator driver, that's why AEN support
is not present in the ib_srpt driver.

But even if ib_srpt sends no SRP_AER_REQ requests, any Linux system that is
connected to it should poll the SRP target system periodically. Both the Linux
SCSI disk (sd) and CD-ROM (sr) drivers poll the target system periodically by
sending a TUR (TEST UNIT READY) command (see also the sd_check_events() and
sr_check_events() functions in drivers/scsi/s[dr].c). How often SCSI devices
are polled can be controlled through /sys/block/*/events_poll_msecs. A udev
rule (/usr/lib/udev/rules.d/60-block.rules) sets the default polling interval.

Are you sure that you really need asynchronous notifications and that the
polling by the Linux SCSI initiator is not sufficient?

Bart.