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

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Date:   Mon, 6 Jan 2020 08:47:06 +0000
From:   "Singh, Balbir" <sblbir@...zon.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bob.liu@...cle.com" <bob.liu@...cle.com>,
        "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 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?
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

Thanks,
Balbir Singh