It was necessary since an Linux older than 2.6.35 may implement the
virtio-net header but may not allow to change its length. Remove it
since such an old Linux is no longer supported.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
---
 net/tap_int.h     |  1 -
 net/tap-bsd.c     |  5 -----
 net/tap-linux.c   | 20 --------------------
 net/tap-solaris.c |  5 -----
 net/tap-stub.c    |  5 -----
 net/tap.c         |  8 ++------
 6 files changed, 2 insertions(+), 42 deletions(-)

diff --git a/net/tap_int.h b/net/tap_int.h
index 9a2175655b..8857ff299d 100644
--- a/net/tap_int.h
+++ b/net/tap_int.h
@@ -35,7 +35,6 @@ ssize_t tap_read_packet(int tapfd, uint8_t *buf, int maxlen);
 
 void tap_set_sndbuf(int fd, const NetdevTapOptions *tap, Error **errp);
 int tap_probe_vnet_hdr(int fd, Error **errp);
-int tap_probe_vnet_hdr_len(int fd, int len);
 int tap_probe_has_ufo(int fd);
 int tap_probe_has_uso(int fd);
 void tap_fd_set_offload(int fd, int csum, int tso4, int tso6, int ecn, int ufo,
diff --git a/net/tap-bsd.c b/net/tap-bsd.c
index 274ea7bd2c..b4c84441ba 100644
--- a/net/tap-bsd.c
+++ b/net/tap-bsd.c
@@ -217,11 +217,6 @@ int tap_probe_has_uso(int fd)
     return 0;
 }
 
-int tap_probe_vnet_hdr_len(int fd, int len)
-{
-    return 0;
-}
-
 void tap_fd_set_vnet_hdr_len(int fd, int len)
 {
 }
diff --git a/net/tap-linux.c b/net/tap-linux.c
index c7e514ecb0..1226d5fda2 100644
--- a/net/tap-linux.c
+++ b/net/tap-linux.c
@@ -185,26 +185,6 @@ int tap_probe_has_uso(int fd)
     return 1;
 }
 
-/* Verify that we can assign given length */
-int tap_probe_vnet_hdr_len(int fd, int len)
-{
-    int orig;
-    if (ioctl(fd, TUNGETVNETHDRSZ, &orig) == -1) {
-        return 0;
-    }
-    if (ioctl(fd, TUNSETVNETHDRSZ, &len) == -1) {
-        return 0;
-    }
-    /* Restore original length: we can't handle failure. */
-    if (ioctl(fd, TUNSETVNETHDRSZ, &orig) == -1) {
-        fprintf(stderr, "TUNGETVNETHDRSZ ioctl() failed: %s. Exiting.\n",
-                strerror(errno));
-        abort();
-        return -errno;
-    }
-    return 1;
-}
-
 void tap_fd_set_vnet_hdr_len(int fd, int len)
 {
     if (ioctl(fd, TUNSETVNETHDRSZ, &len) == -1) {
diff --git a/net/tap-solaris.c b/net/tap-solaris.c
index 08b13af512..51b7830bef 100644
--- a/net/tap-solaris.c
+++ b/net/tap-solaris.c
@@ -221,11 +221,6 @@ int tap_probe_has_uso(int fd)
     return 0;
 }
 
-int tap_probe_vnet_hdr_len(int fd, int len)
-{
-    return 0;
-}
-
 void tap_fd_set_vnet_hdr_len(int fd, int len)
 {
 }
diff --git a/net/tap-stub.c b/net/tap-stub.c
index 4b24f61e3a..38673434cb 100644
--- a/net/tap-stub.c
+++ b/net/tap-stub.c
@@ -52,11 +52,6 @@ int tap_probe_has_uso(int fd)
     return 0;
 }
 
-int tap_probe_vnet_hdr_len(int fd, int len)
-{
-    return 0;
-}
-
 void tap_fd_set_vnet_hdr_len(int fd, int len)
 {
 }
diff --git a/net/tap.c b/net/tap.c
index c23d0323c2..a1f4d9d49f 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -259,11 +259,7 @@ static bool tap_has_vnet_hdr(NetClientState *nc)
 
 static bool tap_has_vnet_hdr_len(NetClientState *nc, int len)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
-
-    assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
-
-    return !!tap_probe_vnet_hdr_len(s->fd, len);
+    return tap_has_vnet_hdr(nc);
 }
 
 static int tap_get_vnet_hdr_len(NetClientState *nc)
@@ -432,7 +428,7 @@ static TAPState *net_tap_fd_init(NetClientState *peer,
      * Make sure host header length is set correctly in tap:
      * it might have been modified by another instance of qemu.
      */
-    if (tap_probe_vnet_hdr_len(s->fd, s->host_vnet_hdr_len)) {
+    if (vnet_hdr) {
         tap_fd_set_vnet_hdr_len(s->fd, s->host_vnet_hdr_len);
     }
     tap_read_poll(s, true);
-- 
2.42.1