linux-kernel - Re: [PATCH v2 net-next] ptp: Move from simple ida to xarray

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Date: Mon, 11 Mar 2024 14:42:24 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Kory Maincent <kory.maincent@...tlin.com>, Jakub Kicinski
	<kuba@...nel.org>, Simon Horman <horms@...nel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
CC: <thomas.petazzoni@...tlin.com>, Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH v2 net-next] ptp: Move from simple ida to xarray

On 3/11/24 10:21, Kory Maincent wrote:
> Move from simple ida to xarray for storing and loading the ptp_clock
> pointer. This prepares support for future hardware timestamp selection by
> being able to link the ptp clock index to its pointer.
> 
> Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>
> ---
> 
> Change in v2:
> - Update an err value missing
> ---
>   drivers/ptp/ptp_clock.c | 16 ++++++++--------
>   1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
> index 3aaf1a3430c5..9339fd475df0 100644
> --- a/drivers/ptp/ptp_clock.c
> +++ b/drivers/ptp/ptp_clock.c
> @@ -31,7 +31,7 @@ struct class *ptp_class;
>   
>   static dev_t ptp_devt;
>   
> -static DEFINE_IDA(ptp_clocks_map);
> +static DEFINE_XARRAY_ALLOC(ptp_clocks_map);
>   
>   /* time stamp event queue operations */
>   
> @@ -201,7 +201,7 @@ static void ptp_clock_release(struct device *dev)
>   	bitmap_free(tsevq->mask);
>   	kfree(tsevq);
>   	debugfs_remove(ptp->debugfs_root);
> -	ida_free(&ptp_clocks_map, ptp->index);
> +	xa_erase(&ptp_clocks_map, ptp->index);
>   	kfree(ptp);
>   }
>   
> @@ -246,12 +246,12 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
>   	if (ptp == NULL)
>   		goto no_memory;
>   
> -	index = ida_alloc_max(&ptp_clocks_map, MINORMASK, GFP_KERNEL);
> -	if (index < 0) {
> -		err = index;
> +	err = xa_alloc(&ptp_clocks_map, &index, ptp, xa_limit_31b,
> +		       GFP_KERNEL);
> +	if (err)
>   		goto no_slot;
> -	}
>   
> +	err = -ENOMEM;

here it looks weird (even if technically correct),
I would either move the err assignement down, just above next kzalloc()
call, or refactor function to use the following idiom:
   ptr = kzalloc(...)
   if (!ptr) {
       err = -ENOMEM;
       goto somewhere;
   }

(it's already is for @vclock_index field init)

Otherwise context is too small to tell what is the reason.

>   	ptp->clock.ops = ptp_clock_ops;
>   	ptp->info = info;
>   	ptp->devid = MKDEV(major, index);
> @@ -378,7 +378,7 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
>   	list_del(&queue->qlist);
>   	kfree(queue);
>   no_memory_queue:
> -	ida_free(&ptp_clocks_map, index);
> +	xa_erase(&ptp_clocks_map, index);
>   no_slot:
>   	kfree(ptp);
>   no_memory:
> @@ -511,7 +511,7 @@ static void __exit ptp_exit(void)
>   {
>   	class_destroy(ptp_class);
>   	unregister_chrdev_region(ptp_devt, MINORMASK + 1);
> -	ida_destroy(&ptp_clocks_map);
> +	xa_destroy(&ptp_clocks_map);
>   }
>   
>   static int __init ptp_init(void)