linux-kernel - Re: [PATCH 1/7] scsi: ufs: Add Configuration Descriptor to sysfs

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Date:   Mon, 4 Jun 2018 08:39:08 -0700
From:   Evan Green <evgreen@...omium.org>
To:     Bart.VanAssche@....com
Cc:     jejb@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, martin.petersen@...cle.com,
        Vinayak Holikatti <vinholikatti@...il.com>,
        Stanislav.Nijnikov@....com, Gwendal Grignou <gwendal@...omium.org>
Subject: Re: [PATCH 1/7] scsi: ufs: Add Configuration Descriptor to sysfs

On Mon, Jun 4, 2018 at 1:31 AM Bart Van Assche <Bart.VanAssche@....com> wrote:
>
> On Tue, 2018-05-29 at 11:17 -0700, Evan Green wrote:
> > This change adds the configuration descriptor to the UFS
> > sysfs interface. This is done in preparation for making the
> > interface writable, which will enable provisioning UFS devices
> > via Linux.
> >
> > The configuration descriptor is laid out as a header, then a set of
> > (usually 8) copies of the same descriptor for each unit. Rather than
> > creating 8 sets of the same attribute, this interface adds a cfg_unit
> > file, which can be set as an index that defines which of the 8
> > configuration unit descriptors are being shown through sysfs.
>
> I don't know any other example of a sysfs attribute that controls the
> contents of another sysfs attribute so I don't know whether this kind
> of behavior is acceptable for sysfs attributes. Additionally, how can
> these two sysfs attributes be used together from concurrently running
> processes without triggering a race condition?
>
> Bart.

Hi Bart,
I was following the example of rpm_lvl and spm_lvl in this driver,
whose values control what is shown in rpm_target_dev_state and
rpm_target_link_state (and spm equivalents). My original thinking was
that provisioning the high level storage configuration of a UFS disk
is by definition a single threaded one-time-only activity. However
Stanislav and others have also expressed concerns about this
mechanism, so it sounds like I should revise it. I'm hoping Stanislav
will comment on one of two possible approaches I suggested in the
cover letter.

-Evan