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

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH v5 4/4]xfs: xfs_seek_hole() refinements with lookup hole offset from page cache.
From: Jie Liu <jeff.liu@xxxxxxxxxx>
Date: Tue, 31 Jul 2012 16:08:34 +0800
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20120731001322.GN2877@dastard>
References: <50110636.2010602@xxxxxxxxxx> <20120731001322.GN2877@dastard>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120714 Thunderbird/14.0
On 07/31/12 08:13, Dave Chinner wrote:
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.
Thanks for a comprehensive review, I'll fix them according to your comments.

Thanks,
-Jeff

Cheers,

Dave.

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