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vmspawn: convert network device setup to bridge

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Remove the static netdev/nic INI config sections for both privileged
TAP, nsresourced TAP, and user-mode networking. Replace them with a
NetworkInfo struct that captures the network type, TAP fd or interface
name, and MAC address, passed to vmspawn_varlink_setup_network() for
runtime configuration via QMP.

For the nsresourced TAP path the fd is now passed to QEMU via QMP
getfd + SCM_RIGHTS instead of being inherited through pass_fds.

Declare the MachineConfig aggregate that this and the following
conversion patches populate, zero-initialized with explicit -EBADF
for the fd fields so every sub-structure cleans up safely regardless
of which device types the invocation ends up using.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Christian Brauner
2026-04-15 10:14:48 +02:00
parent 0d8fb7d543
commit cc045f5326
1 changed files with 35 additions and 44 deletions
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src/vmspawn/vmspawn.c
+35 -44
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@@ -2335,6 +2335,10 @@ static int run_virtual_machine(int kvm_device_fd, int vhost_device_fd) {
_cleanup_close_ int notify_sock_fd = -EBADF;
_cleanup_strv_free_ char **cmdline = NULL;
_cleanup_free_ int *pass_fds = NULL;
_cleanup_(machine_config_done) MachineConfig config = {
.network = { .fd = -EBADF },
.vsock = { .fd = -EBADF },
};
sd_event_source **children = NULL;
size_t n_children = 0, n_pass_fds = 0;
int r;
@@ -2573,8 +2577,14 @@ static int run_virtual_machine(int kvm_device_fd, int vhost_device_fd) {
return log_oom();
_cleanup_close_ int delegate_userns_fd = -EBADF, tap_fd = -EBADF;
_cleanup_free_ char *tap_name = NULL;
struct ether_addr mac_vm = {};
if (arg_network_stack == NETWORK_STACK_TAP) {
if (have_effective_cap(CAP_NET_ADMIN) <= 0) {
/* Without CAP_NET_ADMIN we use nsresourced to create a TAP device.
* The TAP fd is passed to QEMU via QMP getfd + SCM_RIGHTS after
* the handshake, then referenced by name in netdev_add. */
delegate_userns_fd = userns_acquire_self_root();
if (delegate_userns_fd < 0)
return log_error_errno(delegate_userns_fd, "Failed to acquire userns: %m");
@@ -2596,65 +2606,39 @@ static int run_virtual_machine(int kvm_device_fd, int vhost_device_fd) {
if (tap_fd < 0)
return log_error_errno(tap_fd, "Failed to allocate network tap device: %m");
r = strv_extend(&cmdline, "-netdev");
if (r < 0)
return log_oom();
r = strv_extendf(&cmdline, "tap,id=net0,fd=%i", tap_fd);
if (r < 0)
return log_oom();
r = strv_extend_many(&cmdline, "-device", "virtio-net-pci,netdev=net0");
if (r < 0)
return log_oom();
if (!GREEDY_REALLOC(pass_fds, n_pass_fds + 1))
return log_oom();
pass_fds[n_pass_fds++] = tap_fd;
config.network = (NetworkInfo) {
.type = "tap",
.fd = TAKE_FD(tap_fd),
};
} else {
_cleanup_free_ char *tap_name = NULL;
struct ether_addr mac_vm = {};
/* With CAP_NET_ADMIN we create the TAP interface by name.
* Configure via QMP after QEMU starts. */
tap_name = strjoin("vt-", arg_machine);
if (!tap_name)
return log_oom();
(void) net_shorten_ifname(tap_name, /* check_naming_scheme= */ false);
if (ether_addr_is_null(&arg_network_provided_mac)){
if (ether_addr_is_null(&arg_network_provided_mac)) {
r = net_generate_mac(arg_machine, &mac_vm, VM_TAP_HASH_KEY, 0);
if (r < 0)
return log_error_errno(r, "Failed to generate predictable MAC address for VM side: %m");
} else
mac_vm = arg_network_provided_mac;
r = qemu_config_section(config_file, "netdev", "net0",
"type", "tap",
"ifname", tap_name,
"script", "no",
"downscript", "no");
if (r < 0)
return r;
r = qemu_config_section(config_file, "device", "nic0",
"driver", "virtio-net-pci",
"netdev", "net0",
"mac", ETHER_ADDR_TO_STR(&mac_vm));
if (r < 0)
return r;
config.network = (NetworkInfo) {
.type = "tap",
.ifname = TAKE_PTR(tap_name),
.mac = mac_vm,
.mac_set = true,
.fd = -EBADF,
};
}
} else if (arg_network_stack == NETWORK_STACK_USER) {
r = qemu_config_section(config_file, "netdev", "net0",
"type", "user");
if (r < 0)
return r;
r = qemu_config_section(config_file, "device", "nic0",
"driver", "virtio-net-pci",
"netdev", "net0");
if (r < 0)
return r;
config.network = (NetworkInfo) {
.type = "user",
.fd = -EBADF,
};
} else {
r = strv_extend_many(&cmdline, "-nic", "none");
if (r < 0)
@@ -3621,6 +3605,13 @@ static int run_virtual_machine(int kvm_device_fd, int vhost_device_fd) {
if (r < 0)
return r;
/* Device setup — all before resuming vCPUs */
if (config.network.type) {
r = vmspawn_qmp_setup_network(bridge, &config.network);
if (r < 0)
return r;
}
/* Resume vCPUs and switch to async event processing */
r = vmspawn_qmp_start(bridge);
if (r < 0)