fuse: add flag to turn on async direct IO

Without async DIO write requests to a single file were always serialized.
With async DIO that's no longer the case.

So don't turn on async DIO by default for fear of breaking backward
compatibility.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/file.c

@@ -2371,14 +2371,14 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 			loff_t offset, unsigned long nr_segs)
 {
 	ssize_t ret = 0;
-	struct file *file = NULL;
+	struct file *file = iocb->ki_filp;
+	struct fuse_file *ff = file->private_data;
 	loff_t pos = 0;
 	struct inode *inode;
 	loff_t i_size;
 	size_t count = iov_length(iov, nr_segs);
 	struct fuse_io_priv *io;
 
-	file = iocb->ki_filp;
 	pos = offset;
 	inode = file->f_mapping->host;
 	i_size = i_size_read(inode);
@@ -2403,9 +2403,9 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 	io->file = file;
 	/*
 	 * By default, we want to optimize all I/Os with async request
-	 * submission to the client filesystem.
+	 * submission to the client filesystem if supported.
 	 */
-	io->async = 1;
+	io->async = ff->fc->async_dio;
 	io->iocb = iocb;
 
 	/*

fs/fuse/fuse_i.h

@@ -541,6 +541,9 @@ struct fuse_conn {
 	/** Does the filesystem want adaptive readdirplus? */
 	unsigned readdirplus_auto:1;
 
+	/** Does the filesystem support asynchronous direct-IO submission? */
+	unsigned async_dio:1;
+
 	/** The number of requests waiting for completion */
 	atomic_t num_waiting;
 

fs/fuse/inode.c

@@ -871,6 +871,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 				fc->do_readdirplus = 1;
 			if (arg->flags & FUSE_READDIRPLUS_AUTO)
 				fc->readdirplus_auto = 1;
+			if (arg->flags & FUSE_ASYNC_DIO)
+				fc->async_dio = 1;
 		} else {
 			ra_pages = fc->max_read / PAGE_CACHE_SIZE;
 			fc->no_lock = 1;
@@ -898,7 +900,7 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
 		FUSE_EXPORT_SUPPORT | FUSE_BIG_WRITES | FUSE_DONT_MASK |
 		FUSE_SPLICE_WRITE | FUSE_SPLICE_MOVE | FUSE_SPLICE_READ |
 		FUSE_FLOCK_LOCKS | FUSE_IOCTL_DIR | FUSE_AUTO_INVAL_DATA |
-		FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO;
+		FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO | FUSE_ASYNC_DIO;
 	req->in.h.opcode = FUSE_INIT;
 	req->in.numargs = 1;
 	req->in.args[0].size = sizeof(*arg);

include/uapi/linux/fuse.h

@@ -90,6 +90,9 @@
  * 7.21
  *  - add FUSE_READDIRPLUS
  *  - send the requested events in POLL request
+ *
+ * 7.22
+ *  - add FUSE_ASYNC_DIO
  */
 
 #ifndef _LINUX_FUSE_H
@@ -125,7 +128,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 21
+#define FUSE_KERNEL_MINOR_VERSION 22
 
 /** The node ID of the root inode */
 #define FUSE_ROOT_ID 1
@@ -215,6 +218,7 @@ struct fuse_file_lock {
  * FUSE_AUTO_INVAL_DATA: automatically invalidate cached pages
  * FUSE_DO_READDIRPLUS: do READDIRPLUS (READDIR+LOOKUP in one)
  * FUSE_READDIRPLUS_AUTO: adaptive readdirplus
+ * FUSE_ASYNC_DIO: asynchronous direct I/O submission
  */
 #define FUSE_ASYNC_READ		(1 << 0)
 #define FUSE_POSIX_LOCKS	(1 << 1)
@@ -231,6 +235,7 @@ struct fuse_file_lock {
 #define FUSE_AUTO_INVAL_DATA	(1 << 12)
 #define FUSE_DO_READDIRPLUS	(1 << 13)
 #define FUSE_READDIRPLUS_AUTO	(1 << 14)
+#define FUSE_ASYNC_DIO		(1 << 15)
 
 /**
  * CUSE INIT request/reply flags