This allows users to pass a pre-configured fd to use for the network
interface.

For example:
        kvm run -n mode=tap,fd=3 3<>/dev/net/tap3

Cc: Daniel P. Berrange <berra...@redhat.com>
Cc: Osier Yang <jy...@redhat.com>
Signed-off-by: Sasha Levin <levinsasha...@gmail.com>
---
 tools/kvm/builtin-run.c            |    2 ++
 tools/kvm/include/kvm/virtio-net.h |    1 +
 tools/kvm/virtio/net.c             |    6 ++++++
 3 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/tools/kvm/builtin-run.c b/tools/kvm/builtin-run.c
index 9148d83..924ae80 100644
--- a/tools/kvm/builtin-run.c
+++ b/tools/kvm/builtin-run.c
@@ -220,6 +220,8 @@ static int set_net_param(struct virtio_net_params *p, const 
char *param,
                p->host_ip = strdup(val);
        } else if (strcmp(param, "vhost") == 0) {
                p->vhost = atoi(val);
+       } else if (strcmp(param, "fd") == 0) {
+               p->fd = atoi(val);
        }
 
        return 0;
diff --git a/tools/kvm/include/kvm/virtio-net.h 
b/tools/kvm/include/kvm/virtio-net.h
index dade8cb..a3219b6 100644
--- a/tools/kvm/include/kvm/virtio-net.h
+++ b/tools/kvm/include/kvm/virtio-net.h
@@ -12,6 +12,7 @@ struct virtio_net_params {
        struct kvm *kvm;
        int mode;
        int vhost;
+       int fd;
 };
 
 void virtio_net__init(const struct virtio_net_params *params);
diff --git a/tools/kvm/virtio/net.c b/tools/kvm/virtio/net.c
index 3fb5054..9b93c5d 100644
--- a/tools/kvm/virtio/net.c
+++ b/tools/kvm/virtio/net.c
@@ -178,6 +178,12 @@ static bool virtio_net__tap_init(const struct 
virtio_net_params *params,
        struct sockaddr_in sin = {0};
        struct ifreq ifr;
 
+       /* Did the user already gave us the FD? */
+       if (params->fd) {
+               ndev->tap_fd = params->fd;
+               return 1;
+       }
+
        ndev->tap_fd = open("/dev/net/tun", O_RDWR);
        if (ndev->tap_fd < 0) {
                pr_warning("Unable to open /dev/net/tun");
-- 
1.7.8

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