[PATCH V4 14/22] tap: introduce a helper to get the name of an interface

[Jason Wang <jasowang@redhat.com>]

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>
---
 include/net/tap.h |    1 +
 net/tap-aix.c     |    6 ++++++
 net/tap-bsd.c     |    4 ++++
 net/tap-haiku.c   |    4 ++++
 net/tap-linux.c   |   13 +++++++++++++
 net/tap-solaris.c |    4 ++++
 net/tap_int.h     |    1 +
 7 files changed, 33 insertions(+), 0 deletions(-)

diff --git a/include/net/tap.h b/include/net/tap.h
index a994f20..c3eb85a 100644
--- a/include/net/tap.h
+++ b/include/net/tap.h
@@ -37,6 +37,7 @@ void tap_set_offload(NetClientState *nc, int csum, int tso4, int tso6, int ecn,
 void tap_set_vnet_hdr_len(NetClientState *nc, int len);
 int tap_enable(NetClientState *nc);
 int tap_disable(NetClientState *nc);
+int tap_get_ifname(NetClientState *nc, char *ifname);
 
 int tap_get_fd(NetClientState *nc);
 
diff --git a/net/tap-aix.c b/net/tap-aix.c
index 66e0574..e760e9a 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 cfc7a28..4f22109 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 664d40f..b3b5fbb 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 bdb0a79..3b21662 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 12cc392..214d95e 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 ca1c21b..125f83d 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 */
-- 
1.7.1