linux-kernel - Re: [resend v1 0/5] Add support for block disk resize notification

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Date:   Mon, 6 Jan 2020 17:08:49 +0800
From:   Bob Liu <bob.liu@...cle.com>
To:     "Singh, Balbir" <sblbir@...zon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Cc:     "hch@....de" <hch@....de>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "Chaitanya.Kulkarni@....com" <Chaitanya.Kulkarni@....com>,
        "mst@...hat.com" <mst@...hat.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "Sangaraju, Someswarudu" <ssomesh@...zon.com>
Subject: Re: [resend v1 0/5] Add support for block disk resize notification

On 1/6/20 4:47 PM, Singh, Balbir wrote:
> On Mon, 2020-01-06 at 13:59 +0800, Bob Liu wrote:
>> On 1/2/20 3:53 PM, Balbir Singh wrote:
>>> Allow block/genhd to notify user space about disk size changes
>>> using a new helper disk_set_capacity(), which is a wrapper on top
>>> of set_capacity(). disk_set_capacity() will only notify if
>>> the current capacity or the target capacity is not zero.
>>>
>>
>> set_capacity_and_notify() may be a more straightforward name.
>>
> 
> Yes, agreed.
> 
>>> Background:
>>>
>>> As a part of a patch to allow sending the RESIZE event on disk capacity
>>> change, Christoph (hch@....de) requested that the patch be made generic
>>> and the hacks for virtio block and xen block devices be removed and
>>> merged via a generic helper.
>>>
>>> This series consists of 5 changes. The first one adds the basic
>>> support for changing the size and notifying. The follow up patches
>>> are per block subsystem changes. Other block drivers can add their
>>> changes as necessary on top of this series.
>>>
>>> Testing:
>>> 1. I did some basic testing with an NVME device, by resizing it in
>>> the backend and ensured that udevd received the event.
>>>
>>> NOTE: After these changes, the notification might happen before
>>> revalidate disk, where as it occured later before.
>>>
>>
>> It's better not to change original behavior.
>> How about something like:
>>
>> +void set_capacity_and_notify(struct gendisk *disk, sector_t size, bool
>> revalidate)
>> {
>> 	sector_t capacity = get_capacity(disk);
>>
>> 	set_capacity(disk, size);
>>
>> +        if (revalidate)
>> +		revalidate_disk(disk);
> 
> Do you see a concern with the notification going out before revalidate_disk?

Not aware any, but keep the original behavior is safer especial when not must change..

> I could keep the behaviour and come up with a suitable name
> 
> revalidate_disk_and_notify() (set_capacity is a part of the revalidation
> process), or feel free to suggest a better name
> 

Feel free to add my reviewed-by next version in this series.
Reviewed-by: Bob Liu <bob.liu@...cle.com>

> Thanks,
> Balbir Singh
>