linux-kernel - Re: [Xen-devel] [PATCH v2 2/4] xenbus: limit when state is forced to closed

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Message-ID: <a5506f58-a469-913d-6860-1214fa346089@suse.com>
Date:   Wed, 11 Dec 2019 11:21:20 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     "Durrant, Paul" <pdurrant@...zon.com>,
        Roger Pau Monné <roger.pau@...rix.com>
Cc:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH v2 2/4] xenbus: limit when state is forced to
 closed

On 11.12.19 11:14, Durrant, Paul wrote:
>> -----Original Message-----
>> From: Roger Pau Monné <roger.pau@...rix.com>
>> Sent: 11 December 2019 10:06
>> To: Durrant, Paul <pdurrant@...zon.com>
>> Cc: xen-devel@...ts.xenproject.org; linux-kernel@...r.kernel.org; Juergen
>> Gross <jgross@...e.com>; Stefano Stabellini <sstabellini@...nel.org>;
>> Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> Subject: Re: [Xen-devel] [PATCH v2 2/4] xenbus: limit when state is forced
>> to closed
>>
>> On Tue, Dec 10, 2019 at 11:33:45AM +0000, Paul Durrant wrote:
>>> If a driver probe() fails then leave the xenstore state alone. There is
>> no
>>> reason to modify it as the failure may be due to transient resource
>>> allocation issues and hence a subsequent probe() may succeed.
>>>
>>> If the driver supports re-binding then only force state to closed during
>>> remove() only in the case when the toolstack may need to clean up. This
>> can
>>> be detected by checking whether the state in xenstore has been set to
>>> closing prior to device removal.
>>>
>>> NOTE: Re-bind support is indicated by new boolean in struct
>> xenbus_driver,
>>>        which defaults to false. Subsequent patches will add support to
>>>        some backend drivers.
>>
>> My intention was to specify whether you want to close the
>> backends on unbind in sysfs, so that an user can decide at runtime,
>> rather than having a hardcoded value in the driver.
>>
>> Anyway, I'm less sure whether such runtime tunable is useful at all,
>> so let's leave it out and can always be added afterwards. At the end
>> of day a user wrongly doing a rmmod blkback can always recover
>> gracefully by loading blkback again with your proposed approach to
>> leave connections open on module removal.
>>
>> Sorry for the extra work.
>>
> 
> Does this mean you don't think the extra driver flag is necessary any more? NB: now that xenbus actually takes module references you can't accidentally rmmod any more :-)

I'd like it to be kept, please.

Juergen