[RFC 6/7] CDC-WDM: implement fsync

[Oliver Neukum <oneukum@suse.com>]

Some users want to be very sure that data has gone out to the
device. This needs fsync.

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/class/cdc-wdm.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 242f83118208..6ea03c12380c 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -590,6 +590,33 @@ static ssize_t wdm_read
 	return rv;
 }
 
+/*
+ * The difference to flush is that we wait forever. If you don't like
+ * that behavior, you need to send a signal.
+ */
+
+static int wdm_fsync(struct file *file, loff_t start, loff_t end, int datasync)
+{
+	struct wdm_device *desc = file->private_data;
+	int rv;
+
+	rv = wait_event_interruptible(desc->wait,
+			!test_bit(WDM_IN_USE, &desc->flags) ||
+			test_bit(WDM_DISCONNECTING, &desc->flags));
+
+	if (test_bit(WDM_DISCONNECTING, &desc->flags))
+		return -ENODEV;
+	if (rv < 0)
+		return -EINTR;
+
+	spin_lock_irq(&desc->iuspin);
+	rv = desc->werr;
+	desc->werr = 0;
+	spin_unlock_irq(&desc->iuspin);
+
+	return usb_translate_errors(rv);
+}
+
 static int wdm_flush(struct file *file, fl_owner_t id)
 {
 	struct wdm_device *desc = file->private_data;
@@ -746,6 +773,7 @@ static const struct file_operations wdm_fops = {
 	.owner =	THIS_MODULE,
 	.read =		wdm_read,
 	.write =	wdm_write,
+	.fsync =	wdm_fsync,
 	.open =		wdm_open,
 	.flush =	wdm_flush,
 	.release =	wdm_release,
-- 
2.16.4