[PATCH 29/41] union-mount: Always create topmost directory on open

[Valerie Aurora]

When we open a directory, always create a matching directory on the
top-level.  This way we don't have to go back and create all the
directories on the path to an element when we want to copy it up.

XXX - Turn into #ifdef'able function

Signed-off-by: Jan Blunck <jblunck@xxxxxxx>
Signed-off-by: Valerie Aurora <vaurora@xxxxxxxxxx>
---
 fs/namei.c |   34 ++++++++++++++++++++++++++++++----
 1 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 1f2a214..8d95eb1 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1284,8 +1284,31 @@ static int __link_path_walk(const char *name, struct nameidata *nd)
 		if (err)
 			break;
 
-		if ((nd->flags & LOOKUP_TOPMOST) &&
-		    (nd->um_flags & LAST_LOWLEVEL)) {
+		/*
+		 * We want to create this element on the top level
+		 * file system in two cases:
+		 *
+		 * - We are specifically told to - LOOKUP_TOPMOST.
+		 * - This is a directory, and it does not yet exist on
+		 *   the top level.  Various tricks only work if
+		 *   directories always exist on the top level.
+		 *
+		 * In either case, only create this element on the top
+		 * level if the last element is located on the lower
+		 * level.  If the last element is located on the top
+		 * level, then every single element in the path
+		 * already exists on the top level.
+		 *
+		 * Note that we can assume that the parent is on the
+		 * top level since we always create the directory on
+		 * the top level.
+		 */
+
+		if ((nd->um_flags & LAST_LOWLEVEL) &&
+		    ((next.dentry->d_inode &&
+		      S_ISDIR(next.dentry->d_inode->i_mode) &&
+		      (nd->path.mnt != next.mnt)) ||
+		     (nd->flags & LOOKUP_TOPMOST))) {
 			struct dentry *dentry;
 
 			dentry = union_create_topmost(nd, &this, &next);
@@ -1349,8 +1372,11 @@ last_component:
 		if (err)
 			break;
 
-		if ((nd->flags & LOOKUP_TOPMOST) &&
-		    (nd->um_flags & LAST_LOWLEVEL)) {
+		if ((nd->um_flags & LAST_LOWLEVEL) &&
+		    ((next.dentry->d_inode &&
+		      S_ISDIR(next.dentry->d_inode->i_mode) &&
+		      (nd->path.mnt != next.mnt)) ||
+		     (nd->flags & LOOKUP_TOPMOST))) {
 			struct dentry *dentry;
 
 			dentry = union_create_topmost(nd, &this, &next);
-- 
1.6.3.3

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