On Mon, Nov 03, 2025 at 07:30:57PM -0500, Jeff Layton wrote:

On Tue, 2025-11-04 at 11:14 +1100, NeilBrown wrote:

quoted

On Mon, 03 Nov 2025, Jeff Layton wrote:

quoted

In order to add directory delegation support, we need to break
delegations on the parent whenever there is going to be a change in the
directory.

Add a delegated_inode parameter to struct createdata. Most callers just
leave that as a NULL pointer, but do_mknodat() is changed to wait for a
delegation break if there is one.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/namei.c         | 26 +++++++++++++++++---------
 include/linux/fs.h |  2 +-
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index fdf4e78cd041de8c564b7d1d89a46ba2aaf79d53..e8973000a312fb05ebb63a0d9bd83b9a5f8f805d 100644
--- a/fs/namei.c
+++ b/fs/namei.c

@@ -3487,6 +3487,9 @@ int vfs_create(struct createdata *args)
 
 	mode = vfs_prepare_mode(idmap, dir, mode, S_IALLUGO, S_IFREG);
 	error = security_inode_create(dir, dentry, mode);
+	if (error)
+		return error;
+	error = try_break_deleg(dir, args->delegated_inode);
 	if (error)
 		return error;
 	error = dir->i_op->create(idmap, dir, dentry, mode, args->excl);

@@ -4359,6 +4362,8 @@ static int may_mknod(umode_t mode)
 static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 		unsigned int dev)
 {
+	struct delegated_inode delegated_inode = { };
+	struct createdata cargs = { };

If we must have 'createdata', can it have a 'struct delegated_inode'
rather than a pointer to it?

If we do that, then we'd need some way to signal that the caller
doesn't want to wait on the delegation break. Currently that's
indicated by setting cargs.delegated_inode to NULL. I suppose we could
add a bool for this or something.

I confess that I too am lukewarm on struct createdata. I can live with
it, but it's not clearly a win to me either.

Christian, thoughts?

If two stable voices of the community seem to have consensus that this
isn't worth it then it's obviously fine to not do it.

quoted

quoted

 	struct mnt_idmap *idmap;
 	struct dentry *dentry;
 	struct path path;

@@ -4383,18 +4388,16 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 	switch (mode & S_IFMT) {
 		case 0:
 		case S_IFREG:
-		{
-			struct createdata args = { .idmap = idmap,
-						   .dir = path.dentry->d_inode,
-						   .dentry = dentry,
-						   .mode = mode,
-						   .excl = true };
-
-			error = vfs_create(&args);
+			cargs.idmap = idmap,
+			cargs.dir = path.dentry->d_inode,
+			cargs.dentry = dentry,
+			cargs.delegated_inode = &delegated_inode;
+			cargs.mode = mode,
+			cargs.excl = true,
+			error = vfs_create(&cargs);
 			if (!error)
 				security_path_post_mknod(idmap, dentry);
 			break;
-		}
 		case S_IFCHR: case S_IFBLK:
 			error = vfs_mknod(idmap, path.dentry->d_inode,
 					  dentry, mode, new_decode_dev(dev));

@@ -4406,6 +4409,11 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 	}
 out2:
 	end_creating_path(&path, dentry);
+	if (is_delegated(&delegated_inode)) {
+		error = break_deleg_wait(&delegated_inode);
+		if (!error)
+			goto retry;
+	}
 	if (retry_estale(error, lookup_flags)) {
 		lookup_flags |= LOOKUP_REVAL;
 		goto retry;

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b61873767b37591aecadd147623d7dfc866bef82..cfcb20a7c4ce4b6dcec98b3eccbdb5ec8bab6fa9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h

@@ -2116,12 +2116,12 @@ struct createdata {
 	struct mnt_idmap *idmap;	// idmap of the mount the inode was found from
 	struct inode *dir;		// inode of parent directory
 	struct dentry *dentry;		// dentry of the child file
+	struct delegated_inode *delegated_inode; // returns parent inode, if delegated
 	umode_t mode;			// mode of the child file
 	bool excl;			// whether the file must not yet exist
 };
 
 int vfs_create(struct createdata *);
-
 struct dentry *vfs_mkdir(struct mnt_idmap *, struct inode *,
 			 struct dentry *, umode_t, struct delegated_inode *);
 int vfs_mknod(struct mnt_idmap *, struct inode *, struct dentry *,

-- 
2.51.1

-- 
Jeff Layton [off-list ref]