um: vector: Add dynamic tap interfaces and scripting

Provide functionality roughly compatible with the existing qemu
ifup scripting:
* invocation of an ifup script. The interface name is passed as the
  first and only argument
* allocating tap interfaces on the fly if they are not explicitly
  specified

Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

Author: kot-begemot-uk

arch/um/drivers/vector_user.c

@@ -37,6 +37,7 @@
 #define ID_MAX 2
 
 #define TOKEN_IFNAME "ifname"
+#define TOKEN_SCRIPT "ifup"
 
 #define TRANS_RAW "raw"
 #define TRANS_RAW_LEN strlen(TRANS_RAW)
@@ -53,6 +54,9 @@
 
 #define MAX_UN_LEN 107
 
+static const char padchar[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+static const char *template = "tapXXXXXX";
+
 /* This is very ugly and brute force lookup, but it is done
  * only once at initialization so not worth doing hashes or
  * anything more intelligent
@@ -189,16 +193,21 @@ static int create_raw_fd(char *iface, int flags, int proto)
 	return err;
 }
 
+
 static struct vector_fds *user_init_tap_fds(struct arglist *ifspec)
 {
-	int fd = -1;
+	int fd = -1, i;
 	char *iface;
 	struct vector_fds *result = NULL;
+	bool dynamic = false;
+	char dynamic_ifname[IFNAMSIZ];
+	char *argv[] = {NULL, NULL, NULL, NULL};
 
 	iface = uml_vector_fetch_arg(ifspec, TOKEN_IFNAME);
 	if (iface == NULL) {
-		printk(UM_KERN_ERR "uml_tap: failed to parse interface spec\n");
-		goto tap_cleanup;
+		dynamic = true;
+		iface = dynamic_ifname;
+		srand(getpid());
 	}
 
 	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
@@ -212,14 +221,30 @@ static struct vector_fds *user_init_tap_fds(struct arglist *ifspec)
 	result->remote_addr_size = 0;
 
 	/* TAP */
+	do {
+		if (dynamic) {
+			strcpy(iface, template);
+			for (i = 0; i < strlen(iface); i++) {
+				if (iface[i] == 'X') {
+					iface[i] = padchar[rand() % strlen(padchar)];
+				}
+			}
+		}
+		fd = create_tap_fd(iface);
+		if ((fd < 0) && (!dynamic)) {
+			printk(UM_KERN_ERR "uml_tap: failed to create tun interface\n");
+			goto tap_cleanup;
+		}
+		result->tx_fd = fd;
+		result->rx_fd = fd;
+	} while (fd < 0);
 
-	fd = create_tap_fd(iface);
-	if (fd < 0) {
-		printk(UM_KERN_ERR "uml_tap: failed to create tun interface\n");
-		goto tap_cleanup;
+	argv[0] = uml_vector_fetch_arg(ifspec, TOKEN_SCRIPT);
+	if (argv[0]) {
+		argv[1] = iface;
+		run_helper(NULL, NULL, argv);
 	}
-	result->tx_fd = fd;
-	result->rx_fd = fd;
+
 	return result;
 tap_cleanup:
 	printk(UM_KERN_ERR "user_init_tap: init failed, error %d", fd);
@@ -231,6 +256,7 @@ static struct vector_fds *user_init_hybrid_fds(struct arglist *ifspec)
 {
 	char *iface;
 	struct vector_fds *result = NULL;
+	char *argv[] = {NULL, NULL, NULL, NULL};
 
 	iface = uml_vector_fetch_arg(ifspec, TOKEN_IFNAME);
 	if (iface == NULL) {
@@ -264,6 +290,12 @@ static struct vector_fds *user_init_hybrid_fds(struct arglist *ifspec)
 			"uml_tap: failed to create paired raw socket: %i\n", result->rx_fd);
 		goto hybrid_cleanup;
 	}
+
+	argv[0] = uml_vector_fetch_arg(ifspec, TOKEN_SCRIPT);
+	if (argv[0]) {
+		argv[1] = iface;
+		run_helper(NULL, NULL, argv);
+	}
 	return result;
 hybrid_cleanup:
 	printk(UM_KERN_ERR "user_init_hybrid: init failed");
@@ -407,6 +439,7 @@ static struct vector_fds *user_init_raw_fds(struct arglist *ifspec)
 	int err = -ENOMEM;
 	char *iface;
 	struct vector_fds *result = NULL;
+	char *argv[] = {NULL, NULL, NULL, NULL};
 
 	iface = uml_vector_fetch_arg(ifspec, TOKEN_IFNAME);
 	if (iface == NULL)
@@ -429,6 +462,11 @@ static struct vector_fds *user_init_raw_fds(struct arglist *ifspec)
 		result->remote_addr = NULL;
 		result->remote_addr_size = 0;
 	}
+	argv[0] = uml_vector_fetch_arg(ifspec, TOKEN_SCRIPT);
+	if (argv[0]) {
+		argv[1] = iface;
+		run_helper(NULL, NULL, argv);
+	}
 	return result;
 raw_cleanup:
 	printk(UM_KERN_ERR "user_init_raw: init failed, error %d", err);