Re: [PATCH 4/7] brd: make sector size configurable

[Hannes Reinecke <hare@suse.de>]

On 6/14/23 14:55, Matthew Wilcox wrote:
> On Wed, Jun 14, 2023 at 01:46:34PM +0200, Hannes Reinecke wrote:
>> @@ -43,9 +43,11 @@ struct brd_device {
>>   	 */
>>   	struct xarray	        brd_folios;
>>   	u64			brd_nr_folios;
>> +	unsigned int		brd_sector_shift;
>> +	unsigned int		brd_sector_size;
>>   };
>>   
>> -#define BRD_SECTOR_SHIFT(b) (PAGE_SHIFT - SECTOR_SHIFT)
>> +#define BRD_SECTOR_SHIFT(b) ((b)->brd_sector_shift - SECTOR_SHIFT)
>>   
>>   static pgoff_t brd_sector_index(struct brd_device *brd, sector_t sector)
>>   {
>> @@ -85,7 +87,7 @@ static int brd_insert_folio(struct brd_device *brd, sector_t sector, gfp_t gfp)
>>   {
>>   	pgoff_t idx;
>>   	struct folio *folio, *cur;
>> -	unsigned int rd_sector_order = get_order(PAGE_SIZE);
>> +	unsigned int rd_sector_order = get_order(brd->brd_sector_size);
> 
> Surely max(0, brd->brd_sector_shift - PAGE_SHIFT) ?
> 
Errm. Possibly.

>> @@ -346,6 +353,25 @@ static int brd_alloc(int i)
>>   		return -ENOMEM;
>>   	brd->brd_number		= i;
>>   	list_add_tail(&brd->brd_list, &brd_devices);
>> +	brd->brd_sector_shift = ilog2(rd_blksize);
>> +	if ((1ULL << brd->brd_sector_shift) != rd_blksize) {
>> +		pr_err("rd_blksize %d is not supported\n", rd_blksize);
> 
> Are you trying to require power-of-two here?  We have is_power_of_2()
> for that purpose.
> 
Ah. So let's use that, then :-)

Cheers,

Hannes