Re: [PATCH] w1: simplify allocation of w1_master

[Rosen Penev]

On Thu, Mar 26, 2026 at 3:31 AM Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote:
>
> On 24/03/2026 03:15, Rosen Penev wrote:
> > Convert bus_master to a flexible array member as it's being used as one
> > with the old C89 + 1 pointer trick.
> >
> > Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
> > ---
> >  drivers/w1/w1_int.c | 4 +---
> >  include/linux/w1.h  | 4 ++--
> >  2 files changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/w1/w1_int.c b/drivers/w1/w1_int.c
> > index 19a0ea28e9f3..a0bb97608564 100644
> > --- a/drivers/w1/w1_int.c
> > +++ b/drivers/w1/w1_int.c
> > @@ -31,12 +31,10 @@ static struct w1_master *w1_alloc_dev(u32 id, int slave_count, int slave_ttl,
> >       /*
> >        * We are in process context(kernel thread), so can sleep.
> >        */
> > -     dev = kzalloc(sizeof(struct w1_master) + sizeof(struct w1_bus_master), GFP_KERNEL);
> > +     dev = kzalloc_flex(*dev, bus_master, 1);
> >       if (!dev)
> >               return NULL;
> >
> > -     dev->bus_master = (struct w1_bus_master *)(dev + 1);
> > -
> >       dev->owner              = THIS_MODULE;
> >       dev->max_slave_count    = slave_count;
> >       dev->slave_count        = 0;
> > diff --git a/include/linux/w1.h b/include/linux/w1.h
> > index 064805bfae3f..7379a9ddefc0 100644
> > --- a/include/linux/w1.h
> > +++ b/include/linux/w1.h
> > @@ -236,9 +236,9 @@ struct w1_master {
> >       struct device_driver    *driver;
> >       struct device           dev;
> >
> > -     struct w1_bus_master    *bus_master;
> > -
> >       u32                     seq;
> > +
> > +     struct w1_bus_master    bus_master[];
>
> Code does not use it as flexible array member, does it? Why this cannot
> be just two kzalloc's - one for w1_master and then next for bus_master?
> Or embed it directly (composition) in w1_master?
two kzalloc or kzalloc + kcalloc just does two allocations needlessly.

It can be embedded, yes.
>
> Best regards,
> Krzysztof