Re: [PATCH] fuse: skip lookup during atomic_open() when O_CREAT is set

[Horst Birthelmer]

Hi Jim,

On Fri, Feb 20, 2026 at 01:41:02PM -0700, Jim Harris wrote:
> From: Jim Harris <jim.harris@xxxxxxxxxx>
> 
> When O_CREAT is set, we don't need the lookup. The lookup doesn't
> harm anything, but it's an extra FUSE operation that's not required.
> 
> Signed-off-by: Jim Harris <jim.harris@xxxxxxxxxx>
> ---
>  fs/fuse/dir.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index f25ee47822ad..35f65d49ed2a 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -895,7 +895,8 @@ static int fuse_create_open(struct mnt_idmap *idmap, struct inode *dir,
>  		goto out_err;
>  	}
>  	kfree(forget);
> -	d_instantiate(entry, inode);
> +	d_drop(entry);
> +	d_splice_alias(inode, entry);
>  	entry->d_time = epoch;
>  	fuse_change_entry_timeout(entry, &outentry);
>  	fuse_dir_changed(dir);
> @@ -936,14 +937,15 @@ static int fuse_atomic_open(struct inode *dir, struct dentry *entry,
>  	if (fuse_is_bad(dir))
>  		return -EIO;
>  
> -	if (d_in_lookup(entry)) {
> -		struct dentry *res = fuse_lookup(dir, entry, 0);
> -		if (res || d_really_is_positive(entry))
> -			return finish_no_open(file, res);
> -	}
> +	if (!(flags & O_CREAT)) {
> +		if (d_in_lookup(entry)) {
> +			struct dentry *res = fuse_lookup(dir, entry, 0);
>  
> -	if (!(flags & O_CREAT))
> +			if (res || d_really_is_positive(entry))
> +				return finish_no_open(file, res);
> +		}
>  		return finish_no_open(file, NULL);
> +	}
>  
>  	/* Only creates */
>  	file->f_mode |= FMODE_CREATED;
> -- 
> 2.43.0
> 
> 

I have been looking at that code lately a lot since I was planning to
replace it with a compound.
I'm not entirely convinced that your proposal is the right direction. 
I would involve O_EXCL as well, since that lookup could actually 
help in that case.

Take a look at what Miklos wrote here:
https://lore.kernel.org/linux-fsdevel/CAJfpegsDxsMsyfP4a_5H1q91xFtwcEdu9-WBnzWKwjUSrPNdmw@xxxxxxxxxxxxxx/

Cheers,
Horst