[RFC PATCH 13/53] netfs: Add bounce buffering support

[David Howells <dhowells@redhat.com>]

Add a second xarray struct to netfs_io_request for the purposes of holding
a bounce buffer for when we have to deal with encrypted/compressed data or
if we have to up/download data in blocks larger than we were asked for.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
 fs/netfs/io.c         | 6 +++++-
 fs/netfs/objects.c    | 3 +++
 include/linux/netfs.h | 2 ++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/netfs/io.c b/fs/netfs/io.c
index e9d408e211b8..d8e9cd6ce338 100644
--- a/fs/netfs/io.c
+++ b/fs/netfs/io.c
@@ -643,7 +643,11 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync)
 		return -EIO;
 	}
 
-	rreq->io_iter = rreq->iter;
+	if (test_bit(NETFS_RREQ_USE_BOUNCE_BUFFER, &rreq->flags))
+		iov_iter_xarray(&rreq->io_iter, ITER_DEST, &rreq->bounce,
+				rreq->start, rreq->len);
+	else
+		rreq->io_iter = rreq->iter;
 
 	INIT_WORK(&rreq->work, netfs_rreq_work);
 
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 4396318081bf..0782a284dda8 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -35,6 +35,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	rreq->inode	= inode;
 	rreq->i_size	= i_size_read(inode);
 	rreq->debug_id	= atomic_inc_return(&debug_ids);
+	xa_init(&rreq->bounce);
 	INIT_LIST_HEAD(&rreq->subrequests);
 	refcount_set(&rreq->ref, 1);
 	__set_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags);
@@ -43,6 +44,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	if (rreq->netfs_ops->init_request) {
 		ret = rreq->netfs_ops->init_request(rreq, file);
 		if (ret < 0) {
+			xa_destroy(&rreq->bounce);
 			kfree(rreq);
 			return ERR_PTR(ret);
 		}
@@ -96,6 +98,7 @@ static void netfs_free_request(struct work_struct *work)
 		}
 		kvfree(rreq->direct_bv);
 	}
+	netfs_clear_buffer(&rreq->bounce);
 	kfree_rcu(rreq, rcu);
 	netfs_stat_d(&netfs_n_rh_rreq);
 }
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index e8d702ac6968..a7220e906287 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -196,6 +196,7 @@ struct netfs_io_request {
 	struct iov_iter		iter;		/* Unencrypted-side iterator */
 	struct iov_iter		io_iter;	/* I/O (Encrypted-side) iterator */
 	struct bio_vec		*direct_bv;	/* DIO buffer list (when handling iovec-iter) */
+	struct xarray		bounce;		/* Bounce buffer (eg. for crypto/compression) */
 	void			*netfs_priv;	/* Private data for the netfs */
 	unsigned int		direct_bv_count; /* Number of elements in bv[] */
 	unsigned int		debug_id;
@@ -220,6 +221,7 @@ struct netfs_io_request {
 #define NETFS_RREQ_IN_PROGRESS		5	/* Unlocked when the request completes */
 #define NETFS_RREQ_NONBLOCK		6	/* Don't block if possible (O_NONBLOCK) */
 #define NETFS_RREQ_BLOCKED		7	/* We blocked */
+#define NETFS_RREQ_USE_BOUNCE_BUFFER	8	/* Use bounce buffer */
 	const struct netfs_request_ops *netfs_ops;
 };