tap: introduce a helper to get the name of an interface

This patch introduces a helper tap_get_ifname() to get the device name of tap
device. This is needed when ifname is unspecified in the command line and qemu
were asked to create tap device by itself. In this situation, the name were
allocated by kernel, so if multiqueue is asked, we need to fetch its name after
creating the first queue.

Only linux has this support since it's the only platform that supports
multiqueue tap.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

6 files changed, 32 insertions, 0 deletions

diff --git a/net/tap-aix.c b/net/tap-aix.c
index 66e0574fd7..e760e9a0e7 100644
--- a/net/tap-aix.c
+++ b/net/tap-aix.c
@@ -69,3 +69,9 @@ int tap_fd_disable(int fd)
 {
     return -1;
 }
+
+int tap_fd_get_ifname(int fd, char *ifname)
+{
+    return -1;
+}
+
diff --git a/net/tap-bsd.c b/net/tap-bsd.c
index cfc7a289f8..4f22109e94 100644
--- a/net/tap-bsd.c
+++ b/net/tap-bsd.c
@@ -156,3 +156,7 @@ int tap_fd_disable(int fd)
     return -1;
 }
 
+int tap_fd_get_ifname(int fd, char *ifname)
+{
+    return -1;
+}
diff --git a/net/tap-haiku.c b/net/tap-haiku.c
index 664d40fb4d..b3b5fbb61e 100644
--- a/net/tap-haiku.c
+++ b/net/tap-haiku.c
@@ -70,3 +70,7 @@ int tap_fd_disable(int fd)
     return -1;
 }
 
+int tap_fd_get_ifname(int fd, char *ifname)
+{
+    return -1;
+}
diff --git a/net/tap-linux.c b/net/tap-linux.c
index bdb0a790c8..3b21662c13 100644
--- a/net/tap-linux.c
+++ b/net/tap-linux.c
@@ -261,3 +261,16 @@ int tap_fd_disable(int fd)
     return ret;
 }
 
+int tap_fd_get_ifname(int fd, char *ifname)
+{
+    struct ifreq ifr;
+
+    if (ioctl(fd, TUNGETIFF, &ifr) != 0) {
+        error_report("TUNGETIFF ioctl() failed: %s",
+                     strerror(errno));
+        return -1;
+    }
+
+    pstrcpy(ifname, sizeof(ifr.ifr_name), ifr.ifr_name);
+    return 0;
+}
diff --git a/net/tap-solaris.c b/net/tap-solaris.c
index 12cc392c94..214d95e626 100644
--- a/net/tap-solaris.c
+++ b/net/tap-solaris.c
@@ -236,3 +236,7 @@ int tap_fd_disable(int fd)
     return -1;
 }
 
+int tap_fd_get_ifname(int fd, char *ifname)
+{
+    return -1;
+}
diff --git a/net/tap_int.h b/net/tap_int.h
index ca1c21b451..125f83d5b0 100644
--- a/net/tap_int.h
+++ b/net/tap_int.h
@@ -44,5 +44,6 @@ void tap_fd_set_offload(int fd, int csum, int tso4, int tso6, int ecn, int ufo);
 void tap_fd_set_vnet_hdr_len(int fd, int len);
 int tap_fd_enable(int fd);
 int tap_fd_disable(int fd);
+int tap_fd_get_ifname(int fd, char *ifname);
 
 #endif /* QEMU_TAP_H */