[PATCH v16 03/13] overlayfs: Implement splice-read

David Howells
2023-03-08T14:39:26Z

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
---

Notes:
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 | 33 ++++++++++++++++++++++++++++++++-
1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 7c04f033aadd..a12919e9ccba 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -419,6 +419,37 @@ 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 (!real.file->f_op->splice_read)
+ goto out_fdput;
+
+ ret = rw_verify_area(READ, real.file, ppos, len);
+ if (unlikely(ret < 0))
+ goto out_fdput;
+
+ 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 +726,7 @@ 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,