[PATCH v2 2/3] tools/usbip: persistently forward USB devices on a given bus

@@ -9,6 +9,11 @@ The USB/IP protocol follows a server/client architecture. The server exports the
 USB devices and the clients import them. The device driver for the exported
 USB device runs on the client machine.
 
+Initially the server may choose to export any of its available USB devices,
+based on the busid. The device will remain exported until it's unplugged or
+unbound from the usbip driver. It is also possible to persistently export
+devices on a given bus by monitor when they are plugged in.
+
 The client may ask for the list of the exported USB devices. To get the list the
 client opens a TCP/IP connection to the server, and sends an OP_REQ_DEVLIST
 packet on top of the TCP/IP connection (so the actual OP_REQ_DEVLIST may be sent

@@ -8,12 +8,14 @@
 
 #include <errno.h>
 #include <stdio.h>
+#include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include <getopt.h>
 
 #include "usbip_common.h"
+#include "usbip_monitor.h"
 #include "utils.h"
 #include "usbip.h"
 #include "sysfs_utils.h"

@@ -24,10 +26,17 @@ enum unbind_status {
 	UNBIND_ST_FAILED
 };
 
+struct bind_options {
+	char *busid;
+	bool is_persistent;
+};
+
 static const char usbip_bind_usage_string[] =
 	"usbip bind <args>\n"
-	"    -b, --busid=<busid>    Bind " USBIP_HOST_DRV_NAME ".ko to device "
-	"on <busid>\n";
+	"    -b, --busid=<busid>        Bind " USBIP_HOST_DRV_NAME ".ko to device\n"
+	"                               on <busid>\n"
+	"    -p, --persistent           Persistently monitor the given bus and\n"
+	"                               export USB devices plugged in\n";
 
 void usbip_bind_usage(void)
 {

@@ -127,29 +136,26 @@ static int unbind_other(char *busid)
 	return status;
 }
 
-static int bind_device(char *busid)
+static const char *get_device_devpath(char *busid)
 {
-	int rc;
-	struct udev *udev;
-	struct udev_device *dev;
-	const char *devpath;
+	struct udev *udev = udev_new();
+	const char *devpath = NULL;
+	struct udev_device *dev = udev_device_new_from_subsystem_sysname(udev, "usb", busid);
 
-	/* Check whether the device with this bus ID exists. */
-	udev = udev_new();
-	dev = udev_device_new_from_subsystem_sysname(udev, "usb", busid);
-	if (!dev) {
-		err("device with the specified bus ID does not exist");
-		return -1;
-	}
-	devpath = udev_device_get_devpath(dev);
+	if (dev)
+		devpath = udev_device_get_devpath(dev);
 	udev_unref(udev);
+	return devpath;
+}
 
-	/* If the device is already attached to vhci_hcd - bail out */
-	if (strstr(devpath, USBIP_VHCI_DRV_NAME)) {
-		err("bind loop detected: device: %s is attached to %s\n",
-		    devpath, USBIP_VHCI_DRV_NAME);
-		return -1;
-	}
+static bool is_usb_connected(char *busid)
+{
+	return get_device_devpath(busid) != NULL;
+}
+
+static int bind_available_device(char *busid)
+{
+	int rc;
 
 	rc = unbind_other(busid);
 	if (rc == UNBIND_ST_FAILED) {

@@ -174,36 +180,94 @@ static int bind_device(char *busid)
 		return -1;
 	}
 
-	info("bind device on busid %s: complete", busid);
+	info("device on busid %s: bind complete", busid);
 
 	return 0;
 }
 
+static int bind_device(char *busid)
+{
+	const char *devpath = get_device_devpath(busid);
+
+	/* Check whether the device with this bus ID exists. */
+	if (!devpath) {
+		err("device with the specified bus ID does not exist");
+		return -1;
+	}
+
+	/* If the device is already attached to vhci_hcd - bail out */
+	if (strstr(devpath, USBIP_VHCI_DRV_NAME)) {
+		err("bind loop detected: device: %s is attached to %s\n",
+		    devpath, USBIP_VHCI_DRV_NAME);
+		return -1;
+	}
+
+	return bind_available_device(busid);
+}
+
+static int bind_device_persistently(char *busid)
+{
+	int rc = 0;
+	bool already_connected = is_usb_connected(busid);
+	usbip_monitor_t *monitor = monitor = usbip_monitor_new();
+
+	usbip_monitor_set_busid(monitor, busid);
+	while (rc == 0) {
+		if (!already_connected) {
+			info("device on busid %s: monitor connect", busid);
+			usbip_monitor_await_usb_bind(monitor, USBIP_USB_DRV_NAME);
+		}
+		rc = bind_available_device(busid);
+		if (rc == 0) {
+			info("device on busid %s: monitor disconnect", busid);
+			usbip_monitor_await_usb_bind(monitor, USBIP_HOST_DRV_NAME);
+			usbip_monitor_await_usb_unbind(monitor);
+		}
+		already_connected = false;
+	}
+	usbip_monitor_delete(monitor);
+	return rc;
+}
+
 int usbip_bind(int argc, char *argv[])
 {
 	static const struct option opts[] = {
 		{ "busid", required_argument, NULL, 'b' },
+		{ "persistent",  no_argument, NULL, 'p' },
 		{ NULL,    0,                 NULL,  0  }
 	};
 
+	struct bind_options options = {};
 	int opt;
 	int ret = -1;
 
 	for (;;) {
-		opt = getopt_long(argc, argv, "b:", opts, NULL);
+		opt = getopt_long(argc, argv, "b:p", opts, NULL);
 
 		if (opt == -1)
 			break;
 
 		switch (opt) {
 		case 'b':
-			ret = bind_device(optarg);
-			goto out;
+			options.busid = optarg;
+			break;
+		case 'p':
+			options.is_persistent = true;
+			break;
 		default:
 			goto err_out;
 		}
 	}
 
+	if (!options.busid)
+		goto err_out;
+
+	if (options.is_persistent)
+		ret = bind_device_persistently(options.busid);
+	else
+		ret = bind_device(options.busid);
+	goto out;
+
 err_out:
 	usbip_bind_usage();
 out: