[PATCH v2 1/1] usbip: auto retry for concurrent attach

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This patch adds recovery from false busy state on concurrent attach 
operation.

The procedure of attach operation is as below.

1) Find an unused port in /sys/devices/platform/vhci_hcd/status. 
(userspace)

2) Request attach found port to driver through 
/sys/devices/platform/vhci_hcd/attach. (userspace)

3) Lock table, reserve requested port and unlock table. (vhci driver)

Attaching more than one remote devices concurrently, same unused port 
number will be found in step-1. Then one request will succeed and 
others will fail even though there are some unused ports. 

It is possible to avoid this fail by introdocing userspace exclusive 
control. But it's exaggerated for this special condition. The locking 
itself is done in driver.

With this patch, driver returns EBUSY when requested port has already 
been used. In this case, attach command retries from step-1: finding 
another unused port. If there's no unused port, the attach operation 
will fail. Othrwise it retries automatically using new free port.

Currunt userspace src/usbip_attach.c:import_device() doesn't use the 
errno.

vhci-hcd's interface (only errno) is changed as following.

Current	errno	New errno	Condition
EINVAL		same as left	specified port numbre is in invalid 
range
EAGAIN		same as left	platform_get_drvdata() failed
EINVAL		same as left	specified socket fd is not valid
EINVAL		EBUSY		specified port status is not free

---
Version information

v2)
Gathered usbip_vhci_driver_close() for errors under an exit label.

Signed-off-by: Nobuo Iwata <nobuo.iwata@xxxxxxxxxxxxxxx>
---
 drivers/usb/usbip/vhci_sysfs.c     |  8 ++++++--
 tools/usb/usbip/src/usbip_attach.c | 33 +++++++++++++++++-------------
 2 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
index b96e5b1..5d4be4b 100644
--- a/drivers/usb/usbip/vhci_sysfs.c
+++ b/drivers/usb/usbip/vhci_sysfs.c
@@ -214,7 +214,7 @@ static ssize_t store_detach(struct device *dev, struct device_attribute *attr,
 
 	ret = vhci_port_disconnect(hcd_to_vhci(hcd), rhport);
 	if (ret < 0)
-		return -EINVAL;
+		return ret;
 
 	usbip_dbg_vhci_sysfs("Leave\n");
 
@@ -314,7 +314,11 @@ static ssize_t store_attach(struct device *dev, struct device_attribute *attr,
 		sockfd_put(socket);
 
 		dev_err(dev, "port %d already used\n", rhport);
-		return -EINVAL;
+		/*
+		 * Will be retried from userspace
+		 * if there's another free port.
+		 */
+		return -EBUSY;
 	}
 
 	dev_info(dev, "pdev(%u) rhport(%u) sockfd(%d)\n",
diff --git a/tools/usb/usbip/src/usbip_attach.c b/tools/usb/usbip/src/usbip_attach.c
index 70a6b50..f1e7ddd 100644
--- a/tools/usb/usbip/src/usbip_attach.c
+++ b/tools/usb/usbip/src/usbip_attach.c
@@ -98,27 +98,32 @@ static int import_device(int sockfd, struct usbip_usb_device *udev)
 	rc = usbip_vhci_driver_open();
 	if (rc < 0) {
 		err("open vhci_driver");
-		return -1;
+		goto err_out;
 	}
 
-	port = usbip_vhci_get_free_port();
-	if (port < 0) {
-		err("no free port");
-		usbip_vhci_driver_close();
-		return -1;
-	}
+	do {
+		port = usbip_vhci_get_free_port();
+		if (port < 0) {
+			err("no free port");
+			goto err_driver_close;
+		}
 
-	rc = usbip_vhci_attach_device(port, sockfd, udev->busnum,
-				      udev->devnum, udev->speed);
-	if (rc < 0) {
-		err("import device");
-		usbip_vhci_driver_close();
-		return -1;
-	}
+		rc = usbip_vhci_attach_device(port, sockfd, udev->busnum,
+					      udev->devnum, udev->speed);
+		if (rc < 0 && errno != EBUSY) {
+			err("import device");
+			goto err_driver_close;
+		}
+	} while (rc < 0);
 
 	usbip_vhci_driver_close();
 
 	return port;
+
+err_driver_close:
+	usbip_vhci_driver_close();
+err_out:
+	return -1;
 }
 
 static int query_import_device(int sockfd, char *busid)
-- 
2.1.0

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