Re: [PATCH 2/2] blockdev: don't set S_DAX for misaligned partitions

[Andreas Dilger]

On Aug 14, 2015, at 2:15 PM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
> 
> The dax code doesn't currently support misaligned partitions,
> so disable O_DIRECT via dax until such time as that support
> materializes.
> 
> Suggested-by: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
> Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
> ---
> fs/block_dev.c | 7 +++++++
> 1 file changed, 7 insertions(+)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 1982437..1170f8c 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1241,6 +1241,13 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
> 				goto out_clear;
> 			}
> 			bd_set_size(bdev, (loff_t)bdev->bd_part->nr_sects << 9);
> +			/*
> +			 * If the partition is not aligned on a page
> +			 * boundary, we can't do dax I/O to it.
> +			 */
> +			if ((bdev->bd_part->start_sect % (PAGE_SIZE / 512)) ||
> +			    (bdev->bd_part->nr_sects % (PAGE_SIZE / 512)))

Maybe I'm missing something, but doesn't the second condition above
disable DAX for the case that the 1/2 patch is fixing (i.e. the last
sectors at the end of a non-PAGE_SIZE-multiple device)?  It seems a
shame to disable DAX for the whole device because of the last sector.

> +				bdev->bd_inode->i_flags &= ~S_DAX;
> 		}
> 	} else {
> 		if (bdev->bd_contains == bdev) {
> -- 
> 1.8.3.1


Cheers, Andreas





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