Re: [Outreachy kernel] [RFC PATCH] staging: unisys: visorhba: Convert module from IDR to XArray

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Apr 26, 2021 at 11:50:15AM +0200, Fabio M. De Francesco wrote:
> Converted visorhba from IDR to XArray. The abstract data type XArray is
> more memory-efficient, parallelisable and cache friendly. It takes 
> advantage of RCU to perform lookups without locking.
> 
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
>  .../staging/unisys/visorhba/visorhba_main.c   | 107 +++++++-----------
>  1 file changed, 44 insertions(+), 63 deletions(-)
> 
> diff --git a/drivers/staging/unisys/visorhba/visorhba_main.c b/drivers/staging/unisys/visorhba/visorhba_main.c
> index 4455d26f7c96..851e60ab0c46 100644
> --- a/drivers/staging/unisys/visorhba/visorhba_main.c
> +++ b/drivers/staging/unisys/visorhba/visorhba_main.c
> @@ -6,10 +6,10 @@
>  
>  #include <linux/debugfs.h>
>  #include <linux/kthread.h>
> -#include <linux/idr.h>
>  #include <linux/module.h>
>  #include <linux/seq_file.h>
>  #include <linux/visorbus.h>
> +#include <linux/xarray.h>
>  #include <scsi/scsi.h>
>  #include <scsi/scsi_host.h>
>  #include <scsi/scsi_cmnd.h>
> @@ -23,6 +23,8 @@
>  #define MAX_PENDING_REQUESTS (MIN_NUMSIGNALS * 2)
>  #define VISORHBA_ERROR_COUNT 30
>  
> +static DEFINE_XARRAY_ALLOC(xa_dtstr);
> +
>  static struct dentry *visorhba_debugfs_dir;
>  
>  /* GUIDS for HBA channel type supported by this driver */
> @@ -78,12 +80,6 @@ struct visorhba_devdata {
>  	unsigned int max_buff_len;
>  	int devnum;
>  	struct uiscmdrsp *cmdrsp;
> -	/*
> -	 * allows us to pass int handles back-and-forth between us and
> -	 * iovm, instead of raw pointers
> -	 */
> -	struct idr idr;
> -
>  	struct dentry *debugfs_dir;
>  	struct dentry *debugfs_info;
>  };
> @@ -183,32 +179,16 @@ static struct uiscmdrsp *get_scsipending_cmdrsp(struct visorhba_devdata *ddata,
>  }
>  
>  /*
> - * simple_idr_get - Associate a provided pointer with an int value
> - *		    1 <= value <= INT_MAX, and return this int value;
> - *		    the pointer value can be obtained later by passing
> - *		    this int value to idr_find()
> - * @idrtable: The data object maintaining the pointer<-->int mappings
> - * @p:	      The pointer value to be remembered
> - * @lock:     A spinlock used when exclusive access to idrtable is needed
> - *
> - * Return: The id number mapped to pointer 'p', 0 on failure
> + * simple_xa_dtstr_get - Store a pointer to xa_dtstr xarray
> + * @id: Pointer to ID
> + * @entry: New entry
>   */
> -static unsigned int simple_idr_get(struct idr *idrtable, void *p,
> -				   spinlock_t *lock)
> +static int simple_xa_dtstr_get(u32 *id, void *entry)

What are you trying to really "get" here?  We shouldn't name the
function based on the data type being used.  All we want is some sort of
"token" or hash or something else?  It's hard to tell...

>  {
> -	int id;
> -	unsigned long flags;
> +	int ret = xa_alloc_irq(&xa_dtstr, id, entry, xa_limit_32b, GFP_NOWAIT);
> +	/* TODO: check for and manage errors */

That's a nice TODO, which means we really should not be considering this
patch to be merged, right?

thanks,

greg k-h