From:   David Howells <dhowells@redhat.com>
To:     Jens Axboe <axboe@kernel.dk>, Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>
Cc:     David Howells <dhowells@redhat.com>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Hillf Danton <hdanton@sina.com>, linux-fsdevel@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Christoph Hellwig <hch@lst.de>,
        John Hubbard <jhubbard@nvidia.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        linux-unionfs@vger.kernel.org
Subject: [PATCH v14 05/17] overlayfs: Implement splice-read
Date:   Tue, 14 Feb 2023 17:13:18 +0000
Message-Id: <20230214171330.2722188-6-dhowells@redhat.com>
In-Reply-To: <20230214171330.2722188-1-dhowells@redhat.com>
References: <20230214171330.2722188-1-dhowells@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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
---
 fs/overlayfs/file.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index c9d0c362c7ef..267b61df6fcd 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -419,6 +419,40 @@ 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;
+
+	ret = -EINVAL;
+	if (in->f_flags & O_DIRECT &&
+	    !(real.file->f_mode & FMODE_CAN_ODIRECT))
+		goto out_fdput;
+	if (!real.file->f_op->splice_read)
+		goto out_fdput;
+
+	ret = rw_verify_area(READ, in, ppos, len);
+	if (unlikely(ret < 0))
+		return ret;
+
+	old_cred = ovl_override_creds(file_inode(in)->i_sb);
+	ret = real.file->f_op->splice_read(real.file, ppos, pipe, len, flags);
+
+	revert_creds(old_cred);
+	ovl_file_accessed(in);
+out_fdput:
+	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 +729,7 @@ 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,