Re: [PATCH 2/7] stm class: Replace uuid_t with plain u8 uuid[16]

[Greg Kroah-Hartman]

On Wed, Apr 14, 2021 at 08:47:48PM +0300, Andy Shevchenko wrote:
> On Wed, Apr 14, 2021 at 07:33:38PM +0200, Greg Kroah-Hartman wrote:
> > On Wed, Apr 14, 2021 at 08:12:46PM +0300, Alexander Shishkin wrote:
> > > From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > > 
> > > It appears that uuid_t use in STM code abuses UUID API.
> > 
> > How is it being abused?
> 
> We are using it against the buffer that is u8, and neither uuid_t nor guid_t.

And how should it be used?

> > Moreover,
> > > this type is only useful when we parse user input. Due to above
> > > replace uuid_t with u8 uuid[16] and use uuid_t only when parse
> > > user input.
> > > 
> > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> > > ---
> > >  drivers/hwtracing/stm/p_sys-t.c | 16 ++++++++++------
> > >  1 file changed, 10 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/hwtracing/stm/p_sys-t.c b/drivers/hwtracing/stm/p_sys-t.c
> > > index 360b5c03df95..04d13b3785d3 100644
> > > --- a/drivers/hwtracing/stm/p_sys-t.c
> > > +++ b/drivers/hwtracing/stm/p_sys-t.c
> > > @@ -76,7 +76,7 @@ enum sys_t_message_string_subtype {
> > >  				 MIPI_SYST_SEVERITY(MAX))
> > >  
> > >  struct sys_t_policy_node {
> > > -	uuid_t		uuid;
> > > +	u8		uuid[UUID_SIZE];
> > 
> > This feels wrong, what is wrong with the uuid_t type usage here?
> 
> Nothing, just will require additional export_uuid() / import_uuid() call.

Isn't that the "correct way" here?

> > >  	bool		do_len;
> > >  	unsigned long	ts_interval;
> > >  	unsigned long	clocksync_interval;
> > > @@ -92,7 +92,7 @@ static void sys_t_policy_node_init(void *priv)
> > >  {
> > >  	struct sys_t_policy_node *pn = priv;
> > >  
> > > -	generate_random_uuid(pn->uuid.b);
> > 
> > Ok, that's not good, but that looks to be a flaw in the
> > generate_random_uuid() api, not this driver implementation.
> > 
> > I don't understand why this change is needed?
> 
> Using raw buffer APIs against uuid_t / guid_t.

So you want to do that, or you do not want to do that?  Totally
confused,

greg k-h