On Wed, 2014-08-06 at 14:35 +0300, Boaz Harrosh wrote:
> 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.
> Note that blk_queue_physical_block_size() also trashes io_min, but
> we can leave this one to be 512.
>
> Signed-off-by: Boaz Harrosh <b...@plexistor.com>
> ---
> drivers/block/brd.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
> index 9673704..514cfe1 100644
> --- a/drivers/block/brd.c
> +++ b/drivers/block/brd.c
> @@ -495,10 +495,17 @@ 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
> + */
> + blk_queue_physical_block_size(brd->brd_queue, PAGE_SIZE);
> + brd->brd_queue->limits.io_min = 512; /* Don't use the accessor */
> +
> 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;
Is there an error case that this patch fixes? I've had page alignment checks
in my PRD direct_access code forever, and I don't know if they've ever
tripped.
Also, blk_queue_physical_block_size() seems wrong - here's the comment for
that function:
/**
* blk_queue_physical_block_size - set physical block size for the queue
* @q: the request queue for the device
* @size: the physical block size, in bytes
*
* Description:
* This should be set to the lowest possible sector size that the
* hardware can operate on without reverting to read-modify-write
* operations.
*/
It doesn't sound like this is what you're after? It sounds like instead you
want to control the alignment, not minimum natural I/O size? It seems like if
you did want to do this, blk_queue_alignment_offset() would be more what you
were after?
- Ross
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