Re: [PATCH v2 17/22] drivers/base: Make device_find_child_by_name() compatible with sysfs inputs

[Dan Williams]

On Sun, Jul 12, 2020 at 10:09 AM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx>
> > Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > ---
> >  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().

This arrangement avoids one of the design mistakes of libnvdimm which
uses a sysfs attribute of the device to delete itself. Parent-device
triggered deletion rather than self-deletion avoids those locking
entanglements.