From: Boaz Harrosh <boaz@xxxxxxxxxxxxx> Because of the direct_access() API which returns a PFN. partitions better start on 4K boundary, else offset ZERO of a partition will not be aligned and blk_direct_access() will fail the call. By setting blk_queue_physical_block_size(PAGE_SIZE) we can communicate this to fdisk and friends. The call to blk_queue_physical_block_size() is harmless and will not affect the Kernel behavior in any way. It is only for communication to user-mode. before this patch running fdisk on a default size brd of 4M the first sector offered is 34 (BAD), but after this patch it will be 40, ie 8 sectors aligned. Also when entering some random partition sizes the next partition-start sector is offered 8 sectors aligned after this patch. (Please note that with fdisk the user can still enter bad values, only the offered default values will be correct) Note that with bdev-size > 4M fdisk will try to align on a 1M boundary (above first-sector will be 2048), in any case. CC: Martin K. Petersen <martin.petersen@xxxxxxxxxx> Signed-off-by: Boaz Harrosh <boaz@xxxxxxxxxxxxx> --- drivers/block/brd.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/block/brd.c b/drivers/block/brd.c index a7463c959..c01b921 100644 --- a/drivers/block/brd.c +++ b/drivers/block/brd.c @@ -486,10 +486,19 @@ static struct brd_device *brd_alloc(int i) brd->brd_queue = blk_alloc_queue(GFP_KERNEL); if (!brd->brd_queue) goto out_free_dev; + blk_queue_make_request(brd->brd_queue, brd_make_request); blk_queue_max_hw_sectors(brd->brd_queue, 1024); blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY); + /* This is so fdisk will align partitions on 4k, because of + * direct_access API needing 4k alignment, returning a PFN + * (This is only a problem on very small devices <= 4M, + * otherwise fdisk will align on 1M. Regardless this call + * is harmless) + */ + blk_queue_physical_block_size(brd->brd_queue, PAGE_SIZE); + brd->brd_queue->limits.discard_granularity = PAGE_SIZE; brd->brd_queue->limits.max_discard_sectors = UINT_MAX; brd->brd_queue->limits.discard_zeroes_data = 1; -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
