Re: [PATCH 1/3] xfs: helper to set flags on uncached buffer reads

[Dave Chinner <david@xxxxxxxxxxxxx>]

On Wed, Jul 13, 2016 at 12:16:33PM -0400, Brian Foster wrote:
> xfs_buf_read_uncached() allocates an uncached buffer and performs a read
> in one go. As part of the upcoming buftarg I/O accounting mechanism,
> some sites may need to set flags on a buffer before I/O submission.
> 
> Create a new helper to support the ability to set flags on a buffer
> before it is submitted for I/O. This use case is the exception, so
> create a wrapper for the original xfs_buf_read_uncached().
> 
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> ---
>  fs/xfs/xfs_buf.c | 20 +++++++++++++++++---
>  fs/xfs/xfs_buf.h |  4 ++++
>  2 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 4665ff6..f007713 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -693,13 +693,14 @@ xfs_buf_readahead_map(
>   * buffer containing the disk contents or nothing.
>   */
>  int
> -xfs_buf_read_uncached(
> +xfs_buf_read_uncached_flags(
>       struct xfs_buftarg      *target,
>       xfs_daddr_t             daddr,
>       size_t                  numblks,
>       int                     flags,
>       struct xfs_buf          **bpp,
> -     const struct xfs_buf_ops *ops)
> +     const struct xfs_buf_ops *ops,
> +     int                     bflags)
>  {

We already have a flags field being passed in. Why can't that be
used to pass the XBF_NO_IOACCT flag? i.e:

>       ASSERT(bp->b_map_count == 1);
>       bp->b_bn = XFS_BUF_DADDR_NULL;  /* always null for uncached buffers */
>       bp->b_maps[0].bm_bn = daddr;
> -     bp->b_flags |= XBF_READ;
> +     bp->b_flags |= XBF_READ | bflags;

        bp->b_flags |= XBF_READ;
        bp->b_flags |= (flags & XBF_NO_IOACCT);

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx