[dm-devel] [PATCH 2/2] dm-mpath: Remove useless retain_attached_hw_handler parameter

[tang.junhui at zte.com.cn]

Hello Mike:

Thanks for your respond.

> 1) in parse_path() you need to always initialize q
the condition of q initialization is 
if (m->retain_attached_hw_handler)¡±
comparing with previous condition
if (test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags) || 
m->hw_handler_name)
it does not increase the possibility of q initialization.

> 2) setting m->hw_handler_name to attached_handler_name needs to still
   > happen regardless of whether m->hw_handler_name was previously set
The patch does not change the logic above, does it? 

> 3) the "retain_attached_hw_handler" feature should still be allowed on
   > the command line, no sense to break multipath-tools
Yes, actually I am still preparing two other patches now, 
one patch modifies parse_features() to ignore unsupported 
parameter and do not return failure. Another patch modifies 
multipath to remove this parameter also.

> In addition, your patch actually breaks the ability to cope with ¨CEBUSY
> from the call to scsi_dh_attach().  Meaning we wouldn't properly fall
> back to retaining the attached hw handler.
scsi_dh_attach() return ¨CEBUSY only if that device has attached 
a different handle, after previous processing, the handle would 
be same, so it is impossible to return ¨CEBUSY in scsi_dh_attach(),
we do not need to process it.

Regards,
Tang





·¢¼þÈË:         Mike Snitzer <snitzer at redhat.com>
ÊÕ¼þÈË:         tang.junhui at zte.com.cn, 
³­ËÍ:   zhang.kai16 at zte.com.cn, dm-devel at redhat.com, agk at redhat.com
ÈÕÆÚ:   2016/11/29 05:52
Ö÷Ìâ:   Re: [dm-devel] [PATCH 2/2] dm-mpath: Remove useless 
retain_attached_hw_handler parameter
·¢¼þÈË: dm-devel-bounces at redhat.com



On Thu, Nov 24 2016 at  2:11am -0500,
tang.junhui at zte.com.cn <tang.junhui at zte.com.cn> wrote:

> From: "tang.junhui" <tang.junhui at zte.com.cn>
> 
> Hardware handle would be retained no matter parameter
> retain_attached_hw_handler is set or not in the logic
> of current code. So remove this useless parameter.

Right, that wasn't always the case.  Previously (before commit )
dm-mpath would first detach the attached handler.

I'm not completely opposed to removing the code that checks
MPATHF_RETAIN_ATTACHED_HW_HANDLER in parse_path() but your proposed
patch is broken in 2 ways:
1) in parse_path() you need to always initialize q
2) setting m->hw_handler_name to attached_handler_name needs to still
   happen regardless of whether m->hw_handler_name was previously set
3) the "retain_attached_hw_handler" feature should still be allowed on
   the command line, no sense to break multipath-tools

But honestly, I'm not seeing any reason to not just leave the existing
code.

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