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Re: [PATCH v5 4/4]xfs: xfs_seek_hole() refinements with lookup hole offs

To: Jeff Liu <jeff.liu@xxxxxxxxxx>
Subject: Re: [PATCH v5 4/4]xfs: xfs_seek_hole() refinements with lookup hole offset from page cache.
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 31 Jul 2012 10:13:22 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <50110636.2010602@xxxxxxxxxx>
References: <50110636.2010602@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Jul 26, 2012 at 04:56:22PM +0800, Jeff Liu wrote:
> Search possbile hole offset for given range from page cache for unwritten and 
> delayed-allocation extents.
> 
> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
> Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> ---
>  fs/xfs/xfs_file.c |   90 
> +++++++++++++++++++++++++++++++++++++++++++++++------
>  1 files changed, 80 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 15acd4d..1b83549 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1296,9 +1296,9 @@ xfs_seek_hole(
>       struct xfs_inode        *ip = XFS_I(inode);
>       struct xfs_mount        *mp = ip->i_mount;
>       loff_t                  uninitialized_var(offset);
> -     loff_t                  holeoff;
>       xfs_fsize_t             isize;
>       xfs_fileoff_t           fsbno;
> +     xfs_filblks_t           end;
>       uint                    lock;
>       int                     error;
>  
> @@ -1314,20 +1314,90 @@ xfs_seek_hole(
>       }
>  
>       fsbno = XFS_B_TO_FSBT(mp, start);
> -     error = xfs_bmap_first_unused(NULL, ip, 1, &fsbno, XFS_DATA_FORK);
> -     if (error)
> -             goto out_unlock;
> +     end = XFS_B_TO_FSB(mp, isize);
> +
> +     for (;;) {
> +             struct xfs_bmbt_irec    map[2];
> +             int                     nmap = 2;
> +
> +             error = xfs_bmapi_read(ip, fsbno, end - fsbno, map, &nmap,
> +                                    XFS_BMAPI_ENTIRE);
> +             if (error)
> +                     goto out_unlock;
> +
> +             /* No extents at given offset, must be beyond EOF */
> +             if (nmap == 0) {
> +                     error = ENXIO;
> +                     goto out_unlock;
> +             }
>  
> -     holeoff = XFS_FSB_TO_B(mp, fsbno);
> -     if (holeoff <= start)
>               offset = start;
> -     else {
> +             /* Landed in a hole, return */
> +             if (map[0].br_startblock == HOLESTARTBLOCK)
> +                     break;
> +             else {
> +                     /*
> +                      * Landed in an unwritten extent, try to lookup page
> +                      * cache to find holes.
> +                      */

Laned in a data extent is more correct here.

> +                     if (map[0].br_state == XFS_EXT_UNWRITTEN ||
> +                         isnullstartblock(map[0].br_startblock)) {
> +                             /* Probing page cache start from offset */
> +                             if (xfs_find_get_desired_pgoff(inode, &map[0],
> +                                                     HOLE_OFF, &offset))
> +                                     break;
> +                     }

Same logic changes as previous patch:

                if (map[0].br_startblock == HOLESTARTBLOCK)
                        break;
                else if (map[0].br_state == XFS_EXT_UNWRITTEN) {
                        ASSERT(!isnullstartblock(map[0].br_startblock));

                        /* Probing page cache start from offset */
                        if (xfs_find_get_desired_pgoff(inode, &map[0],
                                                HOLE_OFF, &offset))
                                break;
                } else {
                        .....

>               /*
> -              * xfs_bmap_first_unused() could return a value bigger than
> -              * isize if there are no more holes past the supplied offset.
> +              * Both mappings contains data, proceed to the next round of
> +              * search if the current reading offset not beyond or hit EOF.
>                */
> -             offset = min_t(loff_t, holeoff, isize);
> +             fsbno = map[1].br_startoff + map[1].br_blockcount;
> +             start = XFS_FSB_TO_B(mp, fsbno);
> +             if (start >= isize) {
> +                     offset = isize;
> +                     break;
> +             }

And that check can move to the start of the loop, too.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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