linux-kernel - Re: [resend v1 5/5] drivers/scsi/sd.c: Convert to use disk_set

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Date:   Wed, 08 Jan 2020 16:32:28 -0500
From:   "Ewan D. Milne" <emilne@...hat.com>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Singh, Balbir" <sblbir@...zon.com>
Cc:     "axboe@...nel.dk" <axboe@...nel.dk>,
        "Chaitanya.Kulkarni@....com" <Chaitanya.Kulkarni@....com>,
        "mst@...hat.com" <mst@...hat.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "Sangaraju, Someswarudu" <ssomesh@...zon.com>,
        "hch@....de" <hch@....de>
Subject: Re: [resend v1 5/5] drivers/scsi/sd.c: Convert to use
 disk_set_capacity

On Tue, 2020-01-07 at 22:15 -0500, Martin K. Petersen wrote:
> Balbir,
> 
> > > We already emit an SDEV_EVT_CAPACITY_CHANGE_REPORTED event if device
> > > capacity changes. However, this event does not automatically cause
> > > revalidation.
> > 
> > The proposed idea is to not reinforce revalidation, unless explictly
> > specified (in the thread before Bob Liu had suggestions). The goal is
> > to notify user space of changes via RESIZE. SCSI sd can opt out of
> > this IOW, I can remove this if you feel
> > SDEV_EVT_CAPACITY_CHANGE_REPORTED is sufficient for current use cases.

Remember that this event is generated because of a Unit Attention from
the device.  We are only passing on this indication to udev.  It basically
allows automation without having to scrape the log file.  We don't proactively
look. e.g. in the case of SCSI unless you have commands being sent to the
device to return the UA status you won't hear about it.

> 
> I have no particular objection to the code change. I was just observing
> that in the context of sd.c, RESIZE=1 is more of a "your request to
> resize was successful" notification due to the requirement of an
> explicit userland action in case a device reports a capacity change.
>