[PATCH 2/2] blktrace: unlink blk directory on final trace close

[Andy Isaacson <adi@hexapodia.org>]

blktrace fails to completely clean up after itself if BLKTRACESTOP is
called before the final trace file is closed:

% blktrace /dev/sdb &
% exec 6</sys/kernel/debug/block/sdb/trace0
% kill %1
% find /sys/kernel/debug/block/
/sys/kernel/debug/block/
/sys/kernel/debug/block/sdb
/sys/kernel/debug/block/sdb/trace0
% exec 6<&-
% find /sys/kernel/debug/block/
/sys/kernel/debug/block/
/sys/kernel/debug/block/sdb

The proper fix is to move cleanup from BLKTRACESTOP to the close
routine, but that's nontrivial, so here's a simple fix to remove
debug/block/<dev> when the last trace%d file is closed.

Cc: stable@kernel.org
Signed-off-by: Andy Isaacson <adi@hexapodia.org>
---
 kernel/trace/blktrace.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 347fe8e..9b78930 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -383,8 +383,12 @@ static int blk_subbuf_start_callback(struct rchan_buf *buf, void *subbuf,
 
 static int blk_remove_buf_file_callback(struct dentry *dentry)
 {
+	struct dentry *parent = dentry->d_parent;
 	debugfs_remove(dentry);
 
+	if (simple_empty(parent))
+		debugfs_remove(parent);
+
 	return 0;
 }
 
-- 
1.7.1