From c386f64819895165472538884e6e64bc6d32eff9 Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bvanassche@acm.org>
Date: Sun, 24 Feb 2019 06:05:07 +0000
Subject: [PATCH] vdisk_fileio, async mode: Submit direct I/O with the "nowait"
 flag set

git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@7987 d57e44dd-8a1f-0410-8b47-8ef2f437770f
---
 scst/include/backport.h            |  8 ++++++++
 scst/src/dev_handlers/scst_vdisk.c | 21 ++++++++++++++-------
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/scst/include/backport.h b/scst/include/backport.h
index ca0d60682..8011d4921 100644
--- a/scst/include/backport.h
+++ b/scst/include/backport.h
@@ -434,6 +434,14 @@ static inline ssize_t call_write_iter(struct file *file, struct kiocb *kio,
 }
 #endif
 
+/*
+ * See also commit b745fafaf70c ("fs: Introduce RWF_NOWAIT and
+ * FMODE_AIO_NOWAIT") # v4.13.
+ */
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 13, 0)
+#define IOCB_NOWAIT 0
+#endif
+
 /* See also commit bdd1d2d3d251 ("fs: fix kernel_read prototype") # v4.14 */
 #if LINUX_VERSION_CODE < KERNEL_VERSION(4, 14, 0)
 static inline ssize_t
diff --git a/scst/src/dev_handlers/scst_vdisk.c b/scst/src/dev_handlers/scst_vdisk.c
index d208babc8..a6ed3fdf5 100644
--- a/scst/src/dev_handlers/scst_vdisk.c
+++ b/scst/src/dev_handlers/scst_vdisk.c
@@ -3303,13 +3303,20 @@ static enum compl_status_e fileio_exec_async(struct vdisk_cmd_params *p)
 		.ki_complete = fileio_async_complete,
 	};
 	if (virt_dev->o_direct_flag)
-		iocb->ki_flags |= IOCB_DIRECT;
-	if (dir == WRITE) {
-		if (virt_dev->wt_flag && !virt_dev->nv_cache)
-			iocb->ki_flags |= IOCB_DSYNC;
-		ret = call_write_iter(fd, iocb, &iter);
-	} else {
-		ret = call_read_iter(fd, iocb, &iter);
+		iocb->ki_flags |= IOCB_DIRECT | IOCB_NOWAIT;
+	if (dir == WRITE && virt_dev->wt_flag && !virt_dev->nv_cache)
+		iocb->ki_flags |= IOCB_DSYNC;
+	for (;;) {
+		if (dir == WRITE)
+			ret = call_write_iter(fd, iocb, &iter);
+		else
+			ret = call_read_iter(fd, iocb, &iter);
+		if (ret >= 0 || (ret != -EOPNOTSUPP && ret != -EAGAIN))
+			break;
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			iocb->ki_flags &= ~IOCB_NOWAIT;
+		else
+			break;
 	}
 	if (p->async.bvec != p->async.small_bvec)
 		kfree(p->async.bvec);