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

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Message-ID: <aQo5_P5XCsSZhw7N@horms.kernel.org>
Date: Tue, 4 Nov 2025 17:38:04 +0000
From: Simon Horman <horms@...nel.org>
To: Jeff Layton <jlayton@...nel.org>
Cc: Miklos Szeredi <miklos@...redi.hu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
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Subject: Re: [PATCH v4 10/17] vfs: make vfs_create break delegations on
 parent directory

On Mon, Nov 03, 2025 at 07:52:38AM -0500, 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@...nel.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

...

> @@ -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 = { };
>  	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,

Hi Jeff,

I don't think it makes any difference to the generated code.
But I think it would be more intuitive to use ';' rather than ','
at the end of the lines immediately above.

> +			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));

...