linux-kernel - Re: [PATCH 2/7] stm class: Replace uuid

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Date:   Wed, 14 Apr 2021 19:33:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH 2/7] stm class: Replace uuid_t with plain u8 uuid[16]

On Wed, Apr 14, 2021 at 08:12:46PM +0300, Alexander Shishkin wrote:
> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> 
> It appears that uuid_t use in STM code abuses UUID API.

How is it being abused?

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@...ux.intel.com>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> ---
>  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?

>  	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?

thanks,

greg k-h