Re: [PATCH] fuse: skip destination updates for zero-byte copy

[Niels de Vos]

On Thu, 2026-07-23 at 18:07 +0800, Yichong Chen wrote:
> __fuse_copy_file_range() may receive a successful copy reply with
> zero
> bytes copied.  This can happen even though the VFS only calls the
> file
> operation with a non-zero length, for example if the FUSE daemon
> reaches
> EOF while the kernel has stale source size information.
> 
> In that case no data was written to the destination.  Do not
> invalidate
> the destination page cache or update the destination timestamps and
> cached
> size state for a zero-byte copy result.
> 
> Fixes: 88bc7d5097a1 ("fuse: add support for copy_file_range()")
> Signed-off-by: Yichong Chen <chenyichong@xxxxxxxxxxxxx>
> ---
>  fs/fuse/file.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index ceada75310b8..75eb97b26912 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -3040,6 +3040,10 @@ static ssize_t __fuse_copy_file_range(struct
> file *file_in, loff_t pos_in,
>  		err = -EIO;
>  		goto out;
>  	}
> +	if (!bytes_copied) {
> +		err = 0;
> +		goto out;
> +	}
>  
>  	truncate_inode_pages_range(inode_out->i_mapping,
>  				   ALIGN_DOWN(pos_out, PAGE_SIZE),

Thanks, this looks good to me.

My style preference would be to make it an "else if" because bytes_copied is
used in the if-statement above already too. I don't think it is required to
adjust this, the functioning will remain the same.

Acked-by: Niels de Vos <ndevos@xxxxxxx>