Re: [PATCH 1/2] dax: fix O_DIRECT I/O to the last block of a blockdev

[Linda Knippers <linda.knippers@hp.com>]

On 8/14/2015 4:15 PM, Jeff Moyer wrote:
> commit bbab37ddc20b (block: Add support for DAX reads/writes to
> block devices) caused a regression in mkfs.xfs.  That utility
> sets the block size of the device to the logical block size
> using the BLKBSZSET ioctl, and then issues a single sector read
> from the last sector of the device.  This results in the dax_io
> code trying to do a page-sized read from 512 bytes from the end
> of the device.  The result is -ERANGE being returned to userspace.
> 
> The fix is to align the block to the page size before calling
> get_block.
> 
> Thanks to willy for simplifying my original patch.
> 
> Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

Tested-by:  Linda Knippers <linda.knippers@hp.com>

> ---
>  fs/dax.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index a7f77e1..ef35a20 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -116,7 +116,8 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
>  		unsigned len;
>  		if (pos == max) {
>  			unsigned blkbits = inode->i_blkbits;
> -			sector_t block = pos >> blkbits;
> +			long page = pos >> PAGE_SHIFT;
> +			sector_t block = page << (PAGE_SHIFT - blkbits);
>  			unsigned first = pos - (block << blkbits);
>  			long size;
>  
>