Re: [PATCH v4 10/17] vfs: make vfs_create break delegations on parent directory

[NeilBrown]

On Mon, 03 Nov 2025, Jeff Layton wrote:
> 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@xxxxxxxxxx>
> ---
>  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?

NeilBrown


>  	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
> 
>