Message-ID: <52157A08.7080701@oracle.com>
Date: Thu, 22 Aug 2013 10:40:08 +0800
From: Joe Jin <joe.jin@oracle.com>
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To: Mike Snitzer <snitzer@redhat.com>
CC: Mikulas Patocka <mpatocka@redhat.com>, dm-devel@redhat.com, agk@redhat.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] dm ioctl: allow change device target type to error
References: <5214CC25.1070307@oracle.com> <alpine.LRH.2.02.1308211041180.10797@file01.intranet.prod.int.rdu2.redhat.com> <20130821150547.GA10987@redhat.com>
In-Reply-To: <20130821150547.GA10987@redhat.com>
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On 08/21/13 23:06, Mike Snitzer wrote:
> On Wed, Aug 21 2013 at 10:48am -0400,
> Mikulas Patocka <mpatocka@redhat.com> wrote:
> 
>>
>>
>> On Wed, 21 Aug 2013, Joe Jin wrote:
>>
>>> commit a5664da "dm ioctl: make bio or request based device type immutable"
>>> prevented "dmsetup wape_table" change the target type to "error".
>>
>> That commit a5664da is there for a reason (it is not possible to change 
>> bio-based device to request-based and vice versa) and I don't really see 
>> how this patch is supposed to work.
>>
>> If there are bios that are in flight and that already passed through 
>> blk_queue_bio, and you change the device from request-based to bio-based, 
>> what are you going to do with them? - The patch doesn't do anything about 
>> it.
>>
>> A better approach would be to create a new request-based target "error-rq" 
>> and change the multipath target to "error-rq" target. That way, you don't 
>> have to change device type from request based to bio based.
> 
> My thoughts _exactly_.  This patch is very confused.
> 
> Joe, what are you looking to be able to do?  Switch a dm-multipath
> device to error?  Or allowing switching a target that has
> DM_TARGET_IMMUTABLE flag set to be switched to error target?
> 
> The latter restriction was introduced with commit 36a0456fb ("dm table:
> add immutable feature").

Hi Mike,

So far dmsetup support wipe_table:
https://bugzilla.redhat.com/show_bug.cgi?id=742607
As description in the bug Doc Text, "This could be useful, for example, 
if a long-running process keeps a device open after it has finished using
it and you need to release the underlying devices before that process exits."

After apply the commit, wipe_table no long works.

Thanks,
Joe
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