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 66e0574fd..e760e9a0e 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 cfc7a289f..4f22109e9 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 664d40fb4..b3b5fbb61 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 bdb0a790c..3b21662c1 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 12cc392c9..214d95e62 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 ca1c21b45..125f83d5b 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 */