Re: [PATCH v21 10/30] overlayfs: Implement splice-read

[Christian Brauner <brauner@kernel.org>]

[Cc Amir as well]

On Sat, May 20, 2023 at 01:00:29AM +0100, David Howells wrote:
> Implement splice-read for overlayfs by passing the request down a layer
> rather than going through generic_file_splice_read() which is going to be
> changed to assume that ->read_folio() is present on buffered files.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Christoph Hellwig <hch@lst.de>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Al Viro <viro@zeniv.linux.org.uk>
> cc: John Hubbard <jhubbard@nvidia.com>
> cc: David Hildenbrand <david@redhat.com>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: Miklos Szeredi <miklos@szeredi.hu>
> cc: linux-unionfs@vger.kernel.org
> cc: linux-block@vger.kernel.org
> cc: linux-fsdevel@vger.kernel.org
> cc: linux-mm@kvack.org
> ---

Acked-by: Christian Brauner <brauner@kernel.org>

> 
> Notes:
>     ver #17)
>      - Use vfs_splice_read() helper rather than open-coding checks.
>     
>     ver #15)
>      - Remove redundant FMODE_CAN_ODIRECT check on real file.
>      - Do rw_verify_area() on the real file, not the overlay file.
>      - Fix a file leak.
> 
>  fs/overlayfs/file.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 7c04f033aadd..86197882ff35 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -419,6 +419,27 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
>  	return ret;
>  }
>  
> +static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
> +			       struct pipe_inode_info *pipe, size_t len,
> +			       unsigned int flags)
> +{
> +	const struct cred *old_cred;
> +	struct fd real;
> +	ssize_t ret;
> +
> +	ret = ovl_real_fdget(in, &real);
> +	if (ret)
> +		return ret;
> +
> +	old_cred = ovl_override_creds(file_inode(in)->i_sb);
> +	ret = vfs_splice_read(real.file, ppos, pipe, len, flags);
> +	revert_creds(old_cred);
> +	ovl_file_accessed(in);
> +
> +	fdput(real);
> +	return ret;
> +}
> +
>  /*
>   * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
>   * due to lock order inversion between pipe->mutex in iter_file_splice_write()
> @@ -695,7 +716,7 @@ const struct file_operations ovl_file_operations = {
>  	.fallocate	= ovl_fallocate,
>  	.fadvise	= ovl_fadvise,
>  	.flush		= ovl_flush,
> -	.splice_read    = generic_file_splice_read,
> +	.splice_read    = ovl_splice_read,
>  	.splice_write   = ovl_splice_write,
>  
>  	.copy_file_range	= ovl_copy_file_range,
>