On 07/31/12 08:06, Dave Chinner wrote:
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.
Will fix it.
+ * 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....
Just done a quick test with above modifications, it works to me, thanks.
+ /*
+ * 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?
If put this check at the beginning of the loop, the code block would
looks like below:
isize = i_size_read(inode);
if (start >= isize) {
error = ENXIO;
goto out_unlock;
}
.......
for (;;) {
struct xfs_bmbt_irec map[2];
int nmap = 2;
if (start >= isize) {
error = ENXIO;
goto out_unlock;
}
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;
}
..........
.....
/*
* 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);
}
But we have a similar check up at the begnning of xfs_seek_data(), will
it looks a bit weird?
Thanks,
-Jeff
Cheers,
Dave.
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