linux-kernel - Re: [RFC PATCH] block/genhd: Notify udev about capacity change

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Message-ID: <8dee699c66a2c8532bd82515291d7fa86cab93f4.camel@amazon.com>
Date:   Fri, 13 Dec 2019 09:13:10 +0000
From:   "Singh, Balbir" <sblbir@...zon.com>
To:     "hch@....de" <hch@....de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "mst@...hat.com" <mst@...hat.com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "Sangaraju, Someswarudu" <ssomesh@...zon.com>
Subject: Re: [RFC PATCH] block/genhd: Notify udev about capacity change

On Thu, 2019-12-12 at 10:54 +0100, Christoph Hellwig wrote:
> On Tue, Dec 10, 2019 at 03:01:31AM +0000, Balbir Singh wrote:
> > Allow block/genhd to notify user space (via udev) 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 via udev if
> > the current capacity or the target capacity is not zero.
> > 
> > disk_set_capacity() is not enabled for all devices, just virtio block,
> > xen-blockfront, nvme and sd. Owners of other block disk devices can
> > easily move over by changing set_capacity() to disk_set_capacity()
> > 
> > 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.
> > 
> > Testing:
> > 1. I did some basic testing with an NVME device, by resizing it in
> > the backend and ensured that udevd received the event.
> > 
> > Suggested-by: Christoph Hellwig <hch@....de>
> > Signed-off-by: Balbir Singh <sblbir@...zon.com>
> > Signed-off-by: Someswarudu Sangaraju <ssomesh@...zon.com>
> > ---
> >  block/genhd.c                | 19 +++++++++++++++++++
> >  drivers/block/virtio_blk.c   |  4 +---
> >  drivers/block/xen-blkfront.c |  5 +----
> >  drivers/nvme/host/core.c     |  2 +-
> >  drivers/scsi/sd.c            |  2 +-
> >  include/linux/genhd.h        |  1 +
> >  6 files changed, 24 insertions(+), 9 deletions(-)
> > 
> > diff --git a/block/genhd.c b/block/genhd.c
> > index ff6268970ddc..94faec98607b 100644
> > --- a/block/genhd.c
> > +++ b/block/genhd.c
> > @@ -46,6 +46,25 @@ static void disk_add_events(struct gendisk *disk);
> >  static void disk_del_events(struct gendisk *disk);
> >  static void disk_release_events(struct gendisk *disk);
> >  
> > +/*
> > + * Set disk capacity and notify if the size is not currently
> > + * zero and will not be set to zero
> 
> Nit: Use up all the 80 chars per line.  Also maybe turn this into a
> kerneldoc comment.  I think you also want to mention the notification
> as well.

Will do!

> 
> > +EXPORT_SYMBOL_GPL(disk_set_capacity);
> > +
> > +
> >  void part_inc_in_flight(struct request_queue *q, struct hd_struct *part,
> > int rw)
> 
> No need for the double empty line.
> 
> >  {
> >  	if (queue_is_mq(q))
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 7ffd719d89de..869cd3c31529 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> 
> And you probably want to turn this into a series with patch 1 adding
> the infrastructure, and then one patch per driver switched over.
Makes sense, will do

Thanks for the feedback
Balbir Singh.