[PATCH 2/3] populate: ensure btree directories are created reliably

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

The population function creates an XFS btree format directory by
polling the extent count of the inode and creating new dirents until
the extent count goes over the limit that pushes it into btree
format.

It then removes every second dirent to create empty space in the
directory data to ensure that operations like metadump with
obfuscation can check that they don't leak stale data from deleted
dirents.

Whilst this does not result in directory data blocks being freed, it
does not take into account the fact that the dabtree index has half
the entries removed from it and that can result in btree nodes
merging and extents being freed. This causes the extent count to go
down, and the inode is converted back into extent form. The
population checks then fail because it should be in btree form.

Fix this by counting the number of directory data extents rather than
the total number of extents in the data fork. We can do this simply
by using xfs_bmap and counting the number of extents returned as it
does not report extents beyond EOF (which is where the dabtree is
located). As the number of data blocks does not change with the
dirent removal algorithm used, this will ensure that the inode data
fork remains in btree format.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 common/populate | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/common/populate b/common/populate
index 9b60fa5c1..7b5b16fb8 100644
--- a/common/populate
+++ b/common/populate
@@ -80,8 +80,11 @@ __populate_create_nfiles() {
 			continue
 		fi
 
-		local nextents="$(_xfs_get_fsxattr nextents $name)"
-		if [ "${nextents}" -gt "${max_nextents}" ]; then
+		# Extent count checks use data blocks only to avoid the removal
+		# step from removing dabtree index blocks and reducing the
+		# number of extents below the required threshold.
+		local nextents="$(xfs_bmap ${name} |grep -v hole | wc -l)"
+		if [ "$((nextents - 1))" -gt "${max_nextents}" ]; then
 			echo ${d}
 			break
 		fi
-- 
2.38.1