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

Christian Brauner
2023-05-20T09:47:33Z

[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,
>