linux-kernel - Re: [PATCH v2 17/22] drivers/base: Make device_find_child_by

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Date:   Mon, 13 Jul 2020 09:36:12 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-nvdimm <linux-nvdimm@...ts.01.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Joao Martins <joao.m.martins@...cle.com>
Subject: Re: [PATCH v2 17/22] drivers/base: Make device_find_child_by_name()
 compatible with sysfs inputs

On Mon, Jul 13, 2020 at 9:13 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Jul 13, 2020 at 09:09:18AM -0700, Dan Williams wrote:
> > On Mon, Jul 13, 2020 at 8:52 AM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Mon, Jul 13, 2020 at 08:39:43AM -0700, Dan Williams wrote:
> > > > On Sun, Jul 12, 2020 at 10:09 AM Greg Kroah-Hartman
> > > > <gregkh@...uxfoundation.org> wrote:
> > > > >
> > > > > On Sun, Jul 12, 2020 at 09:27:37AM -0700, Dan Williams wrote:
> > > > > > Use sysfs_streq() in device_find_child_by_name() to allow it to use a
> > > > > > sysfs input string that might contain a trailing newline.
> > > > > >
> > > > > > The other "device by name" interfaces,
> > > > > > {bus,driver,class}_find_device_by_name(), already account for sysfs
> > > > > > strings.
> > > > > >
> > > > > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > > > > Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> > > > > > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> > > > > > ---
> > > > > >  drivers/base/core.c |    2 +-
> > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > > > > > index 67d39a90b45c..5d31b962c898 100644
> > > > > > --- a/drivers/base/core.c
> > > > > > +++ b/drivers/base/core.c
> > > > > > @@ -3078,7 +3078,7 @@ struct device *device_find_child_by_name(struct device *parent,
> > > > > >
> > > > > >       klist_iter_init(&parent->p->klist_children, &i);
> > > > > >       while ((child = next_device(&i)))
> > > > > > -             if (!strcmp(dev_name(child), name) && get_device(child))
> > > > > > +             if (sysfs_streq(dev_name(child), name) && get_device(child))
> > > > >
> > > > > Who wants to call this function with a name passed from userspace?
> > > > >
> > > > > Not objecting to it, just curious...
> > > > >
> > > >
> > > > The series that incorporates this patch adds a partitioning mechanism
> > > > to "device-dax region" devices with an:
> > > >     "echo 1 > regionX/create" to create a new partition / sub-instance
> > > > of a region, and...
> > > >     "echo $devname > regionX/delete" to delete. Where $devname is
> > > > searched in the child devices of regionX to trigger device_del().
> > >
> > > Shouldn't that be done in configfs, not sysfs?
> >
> > I see configfs as an awkward fit for this situation. configfs wants to
> > software define kernel objects whereas this facility wants to augment
> > existing kernel enumerated device objects. The region device is
> > created by firmware policy and is optionally partitioned, configfs
> > objects don't exist at all until created. So for this I see sysfs +
> > 'scheme to trigger child device creation' as just enough mechanism
> > that does not warrant full blown configfs.
> >
> > I believe it was debates like this [1] that have led me to the camp of
> > sysfs being capable of some device creation dynamism and leave
> > configfs for purely software constructed objects.
> >
> > [1]: https://lore.kernel.org/lkml/17377.42813.479466.690408@cse.unsw.edu.au/
>
> "some" :)

Yes, lowercase and quoted: "some" :).

> And that was from 2006, ugh, how did you find that...

Oh, public-inbox is a wonderful thing. "I kinda sort of remember Neil
laying out a configfs vs sysfs argument", /me searches for "f:neil
configfs" and voila.

> Ok, that's fine, no objection from me for this patch:
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Thanks, Greg.