Re: [PATCH 1/5] fs: don't allow to complete sync iocbs through aio_complete

[Maxim Patlasov <MPatlasov@parallels.com>]

On 01/28/2015 08:57 AM, Christoph Hellwig wrote:
> On Wed, Jan 28, 2015 at 04:30:25PM +0100, Miklos Szeredi wrote:
>> Adding Maxim Patlasov, who did the AIO mode in fuse.
>
> FYI, I don't think fuse should be too hard, it just needs a completion
> in struct fuse_io_priv.  I just didn't bother before getting some higher
> level review for the concept.

Yes, I agree. Here is an example implementation below.

---
 fs/fuse/file.c   |   75 ++++++++++++++++++++++++++++++++++++++----------------
 fs/fuse/fuse_i.h |    1 +
 2 files changed, 54 insertions(+), 22 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index d2be147..b82207a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -528,6 +528,18 @@ static void fuse_release_user_pages(struct fuse_req *req, int write)
 	}
 }
 
+static ssize_t fuse_get_res_by_io(struct fuse_io_priv *io)
+{
+	if (io->err)
+		return io->err;
+
+	if (io->bytes >= 0 && io->write)
+		return -EIO;
+
+	return io->bytes < 0 ? io->size : io->bytes;
+
+}
+
 /**
  * In case of short read, the caller sets 'pos' to the position of
  * actual end of fuse request in IO request. Otherwise, if bytes_requested
@@ -547,6 +559,7 @@ static void fuse_release_user_pages(struct fuse_req *req, int write)
 static void fuse_aio_complete(struct fuse_io_priv *io, int err, ssize_t pos)
 {
 	int left;
+	bool is_sync = is_sync_kiocb(io->iocb);
 
 	spin_lock(&io->lock);
 	if (err)
@@ -555,27 +568,25 @@ static void fuse_aio_complete(struct fuse_io_priv *io, int err, ssize_t pos)
 		io->bytes = pos;
 
 	left = --io->reqs;
-	spin_unlock(&io->lock);
 
-	if (!left) {
-		long res;
+	if (!left && is_sync) {
+		if (io->waiter)
+			wake_up_process(io->waiter);
+	}
 
-		if (io->err)
-			res = io->err;
-		else if (io->bytes >= 0 && io->write)
-			res = -EIO;
-		else {
-			res = io->bytes < 0 ? io->size : io->bytes;
+	spin_unlock(&io->lock);
 
-			if (!is_sync_kiocb(io->iocb)) {
-				struct inode *inode = file_inode(io->iocb->ki_filp);
-				struct fuse_conn *fc = get_fuse_conn(inode);
-				struct fuse_inode *fi = get_fuse_inode(inode);
+	if (!left && !is_sync) {
+		ssize_t res = fuse_get_res_by_io(io);
 
-				spin_lock(&fc->lock);
-				fi->attr_version = ++fc->attr_version;
-				spin_unlock(&fc->lock);
-			}
+		if (res >= 0) {
+			struct inode *inode = file_inode(io->iocb->ki_filp);
+			struct fuse_conn *fc = get_fuse_conn(inode);
+			struct fuse_inode *fi = get_fuse_inode(inode);
+
+			spin_lock(&fc->lock);
+			fi->attr_version = ++fc->attr_version;
+			spin_unlock(&fc->lock);
 		}
 
 		io->iocb->complete(io->iocb, res);
@@ -2798,6 +2809,29 @@ static inline loff_t fuse_round_up(loff_t off)
 	return round_up(off, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
 }
 
+static ssize_t fuse_dio_wait(struct fuse_io_priv *io)
+{
+	ssize_t res;
+
+	spin_lock(&io->lock);
+
+	while (io->reqs) {
+		__set_current_state(TASK_UNINTERRUPTIBLE);
+		io->waiter = current;
+		spin_unlock(&io->lock);
+		io_schedule();
+		/* wake up sets us TASK_RUNNING */
+		spin_lock(&io->lock);
+		io->waiter = NULL;
+	}
+
+	spin_unlock(&io->lock);
+
+	res = fuse_get_res_by_io(io);
+	kfree(io);
+	return res;
+}
+
 static ssize_t
 fuse_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter,
 			loff_t offset)
@@ -2841,10 +2875,8 @@ fuse_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter,
 	/*
 	 * By default, we want to optimize all I/Os with async request
 	 * submission to the client filesystem if supported.
-	 *
-	 * XXX: need to add back support for this mode..
 	 */
-	io->async = async_dio && !is_sync_kiocb(iocb);
+ 	io->async = async_dio;
 	io->iocb = iocb;
 
 	/*
@@ -2867,8 +2899,7 @@ fuse_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter,
 		if (!is_sync_kiocb(iocb))
 			return -EIOCBQUEUED;
 
-		// XXX: need fuse specific replacement
-//		ret = wait_on_sync_kiocb(iocb);
+		ret = fuse_dio_wait(io);
 	} else {
 		kfree(io);
 	}
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 1cdfb07..8d4872b 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -263,6 +263,7 @@ struct fuse_io_priv {
 	int err;
 	struct kiocb *iocb;
 	struct file *file;
+	struct task_struct *waiter;
 };
 
 /**

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