[Qemu-devel] [PATCH] net: Allow specifying ifname for qemu-bridge-helper

[Mike Lovell]

This makes a few changes to allow ifname to be specified when using
qemu-bridge-helper with both the bridge and tap network interfaces. It adds
the --ifname option to qemu-bridge-helper, removes the restriction that ifname
cannot be specified with helper for the tap interface, and adds logic to
specify the --ifname option when exec'ing the helper.

Signed-off-by: Mike Lovell <address@hidden>
---

This feature was originally requested by Mario De Chenno on the qemu-devel
mailing list. Seems pretty simple and figured it was something I could throw
together pretty quickly. I have tested the following combinations of invoking
qemu (where qbr is qemu-bridge-helper)

qemu-system-x86_64 -net nic -net tap,helper="qbr --br=test1"
qemu-system-x86_64 -net nic -net tap,helper="qbr --br=test1",ifname=vm1
qemu-system-x86_64 -net nic -net tap,helper=qbr
qemu-system-x86_64 -net nic -net tap,helper=qbr,ifname=vm1
qemu-system-x86_64 -net nic -net bridge,helper=qbr 
qemu-system-x86_64 -net nic -net bridge,helper=qbr,ifname=vm1
qemu-system-x86_64 -net nic -net bridge,helper=qbr,ifname=vm1,br=test1
qemu-system-x86_64 -net nic -net bridge,helper=qbr,br=test1

 net/tap.c            |   39 ++++++++++++++++++++++++++++-----------
 qapi-schema.json     |    3 ++-
 qemu-bridge-helper.c |   10 +++++++---
 3 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/net/tap.c b/net/tap.c
index a88ae8f..cfb5bff 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -417,11 +417,13 @@ static int recv_fd(int c)
     return len;
 }
 
-static int net_bridge_run_helper(const char *helper, const char *bridge)
+static int net_bridge_run_helper(const char *helper,
+                                 const char *bridge,
+                                 const char *ifname)
 {
     sigset_t oldmask, mask;
     int pid, status;
-    char *args[5];
+    char *args[6];
     char **parg;
     int sv[2];
 
@@ -439,7 +441,9 @@ static int net_bridge_run_helper(const char *helper, const 
char *bridge)
         int open_max = sysconf(_SC_OPEN_MAX), i;
         char fd_buf[6+10];
         char br_buf[6+IFNAMSIZ] = {0};
-        char helper_cmd[PATH_MAX + sizeof(fd_buf) + sizeof(br_buf) + 15];
+        char ifname_buf[10+IFNAMSIZ] = {0};
+        char helper_cmd[PATH_MAX + sizeof(fd_buf) + sizeof(br_buf) +
+                        sizeof(ifname_buf) + 15];
 
         for (i = 0; i < open_max; i++) {
             if (i != STDIN_FILENO &&
@@ -459,8 +463,13 @@ static int net_bridge_run_helper(const char *helper, const 
char *bridge)
                 snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
             }
 
-            snprintf(helper_cmd, sizeof(helper_cmd), "%s %s %s %s",
-                     helper, "--use-vnet", fd_buf, br_buf);
+            if ((strstr(helper, "--ifname=") == NULL) && (ifname != NULL)) {
+                snprintf(ifname_buf, sizeof(ifname_buf), "%s%s" ,
+                         "--ifname=", ifname);
+            }
+
+            snprintf(helper_cmd, sizeof(helper_cmd), "%s %s %s %s %s",
+                     helper, "--use-vnet", fd_buf, br_buf, ifname_buf);
 
             parg = args;
             *parg++ = (char *)"sh";
@@ -473,12 +482,17 @@ static int net_bridge_run_helper(const char *helper, 
const char *bridge)
             /* assume helper is just the executable path name */
 
             snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
+            if (ifname != NULL) {
+                snprintf(ifname_buf, sizeof(ifname_buf), "%s%s" ,
+                         "--ifname=", ifname);
+            }
 
             parg = args;
             *parg++ = (char *)helper;
             *parg++ = (char *)"--use-vnet";
             *parg++ = fd_buf;
             *parg++ = br_buf;
+            *parg++ = ifname_buf;
             *parg++ = NULL;
 
             execv(helper, args);
@@ -517,7 +531,7 @@ int net_init_bridge(const NetClientOptions *opts, const 
char *name,
                     NetClientState *peer)
 {
     const NetdevBridgeOptions *bridge;
-    const char *helper, *br;
+    const char *helper, *br, *ifname;
 
     TAPState *s;
     int fd, vnet_hdr;
@@ -527,8 +541,9 @@ int net_init_bridge(const NetClientOptions *opts, const 
char *name,
 
     helper = bridge->has_helper ? bridge->helper : DEFAULT_BRIDGE_HELPER;
     br     = bridge->has_br     ? bridge->br     : DEFAULT_BRIDGE_INTERFACE;
+    ifname = bridge->has_ifname ? bridge->ifname : NULL;
 
-    fd = net_bridge_run_helper(helper, br);
+    fd = net_bridge_run_helper(helper, br, ifname);
     if (fd == -1) {
         return -1;
     }
@@ -622,14 +637,16 @@ int net_init_tap(const NetClientOptions *opts, const char 
*name,
         model = "tap";
 
     } else if (tap->has_helper) {
-        if (tap->has_ifname || tap->has_script || tap->has_downscript ||
-            tap->has_vnet_hdr) {
-            error_report("ifname=, script=, downscript=, and vnet_hdr= "
+        if (tap->has_script || tap->has_downscript || tap->has_vnet_hdr) {
+            error_report("script=, downscript=, and vnet_hdr= "
                          "are invalid with helper=");
             return -1;
         }
 
-        fd = net_bridge_run_helper(tap->helper, DEFAULT_BRIDGE_INTERFACE);
+        const char *ifname;
+        ifname = tap->has_ifname ? tap->ifname : NULL;
+        fd = net_bridge_run_helper(tap->helper, DEFAULT_BRIDGE_INTERFACE,
+                                   ifname);
         if (fd == -1) {
             return -1;
         }
diff --git a/qapi-schema.json b/qapi-schema.json
index f9dbdae..feaac9e 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2432,7 +2432,8 @@
 { 'type': 'NetdevBridgeOptions',
   'data': {
     '*br':     'str',
-    '*helper': 'str' } }
+    '*helper': 'str',
+    '*ifname': 'str' } }
 
 ##
 # @NetdevHubPortOptions
diff --git a/qemu-bridge-helper.c b/qemu-bridge-helper.c
index 652eec9..c1d1519 100644
--- a/qemu-bridge-helper.c
+++ b/qemu-bridge-helper.c
@@ -67,7 +67,8 @@ typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
 static void usage(void)
 {
     fprintf(stderr,
-            "Usage: qemu-bridge-helper [--use-vnet] --br=bridge 
--fd=unixfd\n");
+            "Usage: qemu-bridge-helper [--use-vnet] [--ifname=name] "
+            "--br=bridge --fd=unixfd\n");
 }
 
 static int parse_acl_file(const char *filename, ACLList *acl_list)
@@ -239,6 +240,7 @@ int main(int argc, char **argv)
     ACLList acl_list;
     int access_allowed, access_denied;
     int ret = EXIT_SUCCESS;
+    const char *ifname = NULL;
 
 #ifdef CONFIG_LIBCAP
     /* if we're run from an suid binary, immediately drop privileges preserving
@@ -259,6 +261,8 @@ int main(int argc, char **argv)
             bridge = &argv[index][5];
         } else if (strncmp(argv[index], "--fd=", 5) == 0) {
             unixfd = atoi(&argv[index][5]);
+        } else if (strncmp(argv[index], "--ifname=", 9) == 0) {
+            ifname = &argv[index][9];
         } else {
             usage();
             return EXIT_FAILURE;
@@ -329,8 +333,8 @@ int main(int argc, char **argv)
     }
 
     /* request a tap device, disable PI, and add vnet header support if
-     * requested and it's available. */
-    prep_ifreq(&ifr, "tap%d");
+     * requested and it's available. use ifname if provided for tap name. */
+    prep_ifreq(&ifr, ifname != NULL ? ifname : "tap%d");
     ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
     if (use_vnet && has_vnet_hdr(fd)) {
         ifr.ifr_flags |= IFF_VNET_HDR;
-- 
1.7.9.5