On Thu, Jul 26, 2012 at 11:32:50PM +0800, Jeff Liu wrote:
> Search data buffer offset for given range from page cache.
>
> 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 | 88 ++++++++++++++++++++++++++++++++++++++++++-----------
> 1 files changed, 70 insertions(+), 18 deletions(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 69965a4..b1158b3 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1182,8 +1182,6 @@ xfs_seek_data(
> struct inode *inode = file->f_mapping->host;
> struct xfs_inode *ip = XFS_I(inode);
> struct xfs_mount *mp = ip->i_mount;
> - struct xfs_bmbt_irec map[2];
> - int nmap = 2;
> loff_t uninitialized_var(offset);
> xfs_fsize_t isize;
> xfs_fileoff_t fsbno;
> @@ -1199,34 +1197,88 @@ xfs_seek_data(
> goto out_unlock;
> }
>
> - fsbno = XFS_B_TO_FSBT(mp, start);
> -
> /*
> * Try to read extents from the first block indicated
> * by fsbno to the end block of the file.
> */
> + fsbno = XFS_B_TO_FSBT(mp, start);
> 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;
> + error = xfs_bmapi_read(ip, fsbno, end - fsbno, map, &nmap,
> + XFS_BMAPI_ENTIRE);
> + if (error)
> + goto out_unlock;
>
> - /*
> - * Treat unwritten extent as data extent since it might
> - * contains dirty data in page cache.
> - */
> - if (map[0].br_startblock != HOLESTARTBLOCK) {
> - offset = max_t(loff_t, start,
> - XFS_FSB_TO_B(mp, map[0].br_startoff));
> - } else {
> - if (nmap == 1) {
> + /* No extents at given offset, must be beyond EOF */
> + if (nmap == 0) {
> error = ENXIO;
> goto out_unlock;
> }
>
> offset = max_t(loff_t, start,
> - XFS_FSB_TO_B(mp, map[1].br_startoff));
> + XFS_FSB_TO_B(mp, map[0].br_startoff));
> + if (map[0].br_state == XFS_EXT_NORM &&
> + !isnullstartblock(map[0].br_startblock))
> + break;
> + else {
> + /*
> + * Landed in an unwritten extent, try to lookup data
Not correct - hole, delay or unwritten land here.
> + * buffer from the page cache before proceeding to
> + * check the next extent map. It's a hole if nothing
> + * was found.
> + */
> + if (map[0].br_startblock == DELAYSTARTBLOCK ||
> + map[0].br_state == XFS_EXT_UNWRITTEN) {
> + /* Probing page cache start from offset */
> + if (xfs_find_get_desired_pgoff(inode, &map[0],
> + DATA_OFF, &offset))
> + break;
> + }
If is is a DELAYSTARTBLOCK, and it is within EOF, then it is
guaranteed to contain data. There is no need for a page cache lookup
to decide where the data starts - by definition the data starts at
map[0].br_startblock. I think you can treat DELAYSTARTBLOCK exactly
the same as allocated XFS_EXT_NORM extents.
That means the logic is:
if (map[0].br_state == XFS_EXT_NORM &&
(!isnullstartblock(map[0].br_startblock) ||
map[0].br_startblock == DELAYSTARTBLOCK)) {
break;
} else if (map[0].br_state == XFS_EXT_UNWRITTEN) {
/* Probing page cache start from offset */
if (xfs_find_get_desired_pgoff(inode, &map[0],
DATA_OFF, &offset))
break;
} else {
/*
* If we find a hole in map[0] and nothing in map[1] it
* probably means that we are reading after EOF.
*/
.....
}
Which kills a level of indentation in the code....
> + /*
> + * Found a hole in map[0] and nothing in map[1].
> + * Probably means that we are reading after EOF.
> + */
> + if (nmap == 1) {
> + error = ENXIO;
> + goto out_unlock;
> + }
> +
> + /*
> + * We have two mappings, proceed to check map[1].
> + */
> + offset = max_t(loff_t, start,
> + XFS_FSB_TO_B(mp, map[1].br_startoff));
> + if (map[1].br_state == XFS_EXT_NORM &&
> + !isnullstartblock(map[1].br_startblock))
> + break;
> + else {
> + /*
> + * map[1] is also an unwritten extent, lookup
> + * data buffer from page cache now.
> + */
> + if (map[1].br_startblock == DELAYSTARTBLOCK ||
> + map[1].br_state == XFS_EXT_UNWRITTEN) {
> + if (xfs_find_get_desired_pgoff(inode,
> + &map[1], DATA_OFF, &offset))
> + break;
> + }
> + }
And the if/elseif/else logic above can be repeated here.
> + }
> +
> + /*
> + * Nothing was found, proceed to the next round of search if
> + * reading offset not beyond or hit EOF.
> + */
> + fsbno = map[1].br_startoff + map[1].br_blockcount;
> + start = XFS_FSB_TO_B(mp, fsbno);
> + if (start >= isize) {
> + error = ENXIO;
> + goto out_unlock;
> + }
Shouldn't this check be done at the start of the loop?
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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