[PATCH RESEND V12 6/8] fuse: Handle asynchronous read and write in passthrough

[Alessio Balsini <balsini@xxxxxxxxxxx>]

Extend the passthrough feature by handling asynchronous IO both for read
and write operations.

When an AIO request is received, if the request targets a FUSE file with
the passthrough functionality enabled, a new identical AIO request is
created. The new request targets the lower file system file and gets
assigned a special FUSE passthrough AIO completion callback.
When the lower file system AIO request is completed, the FUSE
passthrough AIO completion callback is executed and propagates the
completion signal to the FUSE AIO request by triggering its completion
callback as well.

Signed-off-by: Alessio Balsini <balsini@xxxxxxxxxxx>
---
 fs/fuse/passthrough.c | 89 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 78 insertions(+), 11 deletions(-)

diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index d949ca07a83b..c7fa1eeb7639 100644
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -9,6 +9,11 @@
 #define PASSTHROUGH_IOCB_MASK                                                  \
 	(IOCB_APPEND | IOCB_DSYNC | IOCB_HIPRI | IOCB_NOWAIT | IOCB_SYNC)
 
+struct fuse_aio_req {
+	struct kiocb iocb;
+	struct kiocb *iocb_fuse;
+};
+
 static void fuse_copyattr(struct file *dst_file, struct file *src_file)
 {
 	struct inode *dst = file_inode(dst_file);
@@ -17,6 +22,32 @@ static void fuse_copyattr(struct file *dst_file, struct file *src_file)
 	i_size_write(dst, i_size_read(src));
 }
 
+static void fuse_aio_cleanup_handler(struct fuse_aio_req *aio_req)
+{
+	struct kiocb *iocb = &aio_req->iocb;
+	struct kiocb *iocb_fuse = aio_req->iocb_fuse;
+
+	if (iocb->ki_flags & IOCB_WRITE) {
+		__sb_writers_acquired(file_inode(iocb->ki_filp)->i_sb,
+				      SB_FREEZE_WRITE);
+		file_end_write(iocb->ki_filp);
+		fuse_copyattr(iocb_fuse->ki_filp, iocb->ki_filp);
+	}
+
+	iocb_fuse->ki_pos = iocb->ki_pos;
+	kfree(aio_req);
+}
+
+static void fuse_aio_rw_complete(struct kiocb *iocb, long res, long res2)
+{
+	struct fuse_aio_req *aio_req =
+		container_of(iocb, struct fuse_aio_req, iocb);
+	struct kiocb *iocb_fuse = aio_req->iocb_fuse;
+
+	fuse_aio_cleanup_handler(aio_req);
+	iocb_fuse->ki_complete(iocb_fuse, res, res2);
+}
+
 ssize_t fuse_passthrough_read_iter(struct kiocb *iocb_fuse,
 				   struct iov_iter *iter)
 {
@@ -28,9 +59,24 @@ ssize_t fuse_passthrough_read_iter(struct kiocb *iocb_fuse,
 	if (!iov_iter_count(iter))
 		return 0;
 
-	ret = vfs_iter_read(passthrough_filp, iter, &iocb_fuse->ki_pos,
-			    iocb_to_rw_flags(iocb_fuse->ki_flags,
-					     PASSTHROUGH_IOCB_MASK));
+	if (is_sync_kiocb(iocb_fuse)) {
+		ret = vfs_iter_read(passthrough_filp, iter, &iocb_fuse->ki_pos,
+				    iocb_to_rw_flags(iocb_fuse->ki_flags,
+						     PASSTHROUGH_IOCB_MASK));
+	} else {
+		struct fuse_aio_req *aio_req;
+
+		aio_req = kmalloc(sizeof(struct fuse_aio_req), GFP_KERNEL);
+		if (!aio_req)
+			return -ENOMEM;
+
+		aio_req->iocb_fuse = iocb_fuse;
+		kiocb_clone(&aio_req->iocb, iocb_fuse, passthrough_filp);
+		aio_req->iocb.ki_complete = fuse_aio_rw_complete;
+		ret = call_read_iter(passthrough_filp, &aio_req->iocb, iter);
+		if (ret != -EIOCBQUEUED)
+			fuse_aio_cleanup_handler(aio_req);
+	}
 
 	return ret;
 }
@@ -43,20 +89,41 @@ ssize_t fuse_passthrough_write_iter(struct kiocb *iocb_fuse,
 	struct fuse_file *ff = fuse_filp->private_data;
 	struct inode *fuse_inode = file_inode(fuse_filp);
 	struct file *passthrough_filp = ff->passthrough.filp;
+	struct inode *passthrough_inode = file_inode(passthrough_filp);
 
 	if (!iov_iter_count(iter))
 		return 0;
 
 	inode_lock(fuse_inode);
 
-	file_start_write(passthrough_filp);
-	ret = vfs_iter_write(passthrough_filp, iter, &iocb_fuse->ki_pos,
-			     iocb_to_rw_flags(iocb_fuse->ki_flags,
-					      PASSTHROUGH_IOCB_MASK));
-	file_end_write(passthrough_filp);
-	if (ret > 0)
-		fuse_copyattr(fuse_filp, passthrough_filp);
-
+	if (is_sync_kiocb(iocb_fuse)) {
+		file_start_write(passthrough_filp);
+		ret = vfs_iter_write(passthrough_filp, iter, &iocb_fuse->ki_pos,
+				     iocb_to_rw_flags(iocb_fuse->ki_flags,
+						      PASSTHROUGH_IOCB_MASK));
+		file_end_write(passthrough_filp);
+		if (ret > 0)
+			fuse_copyattr(fuse_filp, passthrough_filp);
+	} else {
+		struct fuse_aio_req *aio_req;
+
+		aio_req = kmalloc(sizeof(struct fuse_aio_req), GFP_KERNEL);
+		if (!aio_req) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		file_start_write(passthrough_filp);
+		__sb_writers_release(passthrough_inode->i_sb, SB_FREEZE_WRITE);
+
+		aio_req->iocb_fuse = iocb_fuse;
+		kiocb_clone(&aio_req->iocb, iocb_fuse, passthrough_filp);
+		aio_req->iocb.ki_complete = fuse_aio_rw_complete;
+		ret = call_write_iter(passthrough_filp, &aio_req->iocb, iter);
+		if (ret != -EIOCBQUEUED)
+			fuse_aio_cleanup_handler(aio_req);
+	}
+out:
 	inode_unlock(fuse_inode);
 
 	return ret;
-- 
2.30.0.280.ga3ce27912f-goog