Zephyr OS QEMU: Network Initialization Fails (Cannot Bind to IP, Defaults to 0.0.0.0)

[learnerr2024]

I'm trying to emulate a smart bulb on Zephyr OS using QEMU with networking support. My setup is designed to run an HTTP server on a TAP interface (tap0) configured with specific IPv4 addresses. However, I keep encountering network initialization errors, and Zephyr defaults to binding to 0.0.0.0 instead of the expected IP. Despite configuring tap0 on the host, Zephyr doesn’t seem to recognize the network interface.

Environment

Zephyr OS Version: v4.0.0-rc1

Host OS: Ubuntu

QEMU: Installed via Zephyr SDK

Steps Taken

Configured tap0 Interface on Host:

sudo ip tuntap add dev tap0 mode tap

sudo ip link set tap0 up

sudo ip addr add [192.0.2.1/24](http://192.0.2.1/24) dev tap0

sudo sysctl -w net.ipv4.ip_forward=1`

2.overlay-tap.conf:

CONFIG_NET_L2_ETHERNET=y
CONFIG_NET_SOCKETS=y
CONFIG_NET_CONFIG_SETTINGS=y
CONFIG_NET_CONFIG_MY_IPV4_ADDR="192.0.2.2"
CONFIG_NET_CONFIG_PEER_IPV4_ADDR="192.0.2.1"
CONFIG_NET_CONFIG_MY_IPV4_GW="192.0.2.1"
CONFIG_NET_CONFIG_MY_IPV4_NETMASK="255.255.255.0"

3.prj.conf

#CONFIG_HTTP_SERVER=y
CONFIG_NETWORKING=y
CONFIG_NET_IPV4=y
CONFIG_NET_TCP=y
CONFIG_NET_SOCKETS=y
CONFIG_NET_SLIP_TAP=n
CONFIG_NET_SOCKETS_POSIX_NAMES=y
# Enable logging
CONFIG_LOG=y
CONFIG_NET_LOG=y

4. HTTP Server Code (main.c)

#include <zephyr/kernel.h>
#include <zephyr/net/socket.h>
#include <zephyr/logging/log.h>

LOG_MODULE_REGISTER(http_server, LOG_LEVEL_INF);

#define HTTP_PORT 80
#define HTTP_RESPONSE "HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nContent-Length: 13\r\n\r\nHello, World!"

void start_http_server(void)
{
struct sockaddr_in addr;
int server_fd, client_fd;
char buffer[128];

addr.sin_family = AF_INET;
addr.sin_port = htons(HTTP_PORT);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
server_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

if (server_fd < 0) {
LOG_ERR("Failed to create socket");
return;
}

bind(server_fd, (struct sockaddr *)&addr, sizeof(addr));
listen(server_fd, 5);

while (1) {
client_fd = accept(server_fd, NULL, NULL);
if (client_fd < 0) {
continue;
}

recv(client_fd, buffer, sizeof(buffer) - 1, 0);
send(client_fd, HTTP_RESPONSE, sizeof(HTTP_RESPONSE) - 1, 0);
close(client_fd);
}

close(server_fd);
}

void main(void)
{
LOG_INF("Starting HTTP server...");
start_http_server();
}

west build -b qemu_x86 -- -DOVERLAY_CONFIG=overlay-tap.conf
west build -t run

output:

[00:00:00.000,000] <err> net_if: There is no network interface to work with!
[00:00:00.000,000] <wrn> net_config: No auto-started network interface - network-bound app initialization skipped.
[00:00:00.000,000] <wrn> net_if: No default interface found!
[00:00:00.000,000] <err> net_ctx: Cannot bind to 0.0.0.0`

• Why is Zephyr not binding to the IP address 192.0.2.2 as configured in overlay-tap.conf?
• How can I ensure that QEMU initializes the network interface correctly for Zephyr?
• Are there any specific configurations I might be missing to get networking working properly in QEMU with Zephyr?

[github-actions[bot]]

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Even though I'm a bot, I can assure you that the whole community is genuinely grateful for your time and effort. 🤖💙

[jukkar]

There are ready made scripts found in net-tools project for setting up the tap interface. This is described here https://docs.zephyrproject.org/latest/connectivity/networking/qemu_setup.html#networking-with-qemu

I just tested this and it works fine:

cd zephyrproject/tools/net-tools
./loop-socat.sh

and in another window

cd zephyrproject/tools/net-tools
sudo ./loop-slip-tap.sh

And I started http-server sample like this:

cd zephyrproject/zephyr
west build -p -b qemu_x86 -t run -d ../build/http-server \
samples/net/sockets/http_server/ -- \
-DCONFIG_NET_HTTP_SERVER_LOG_LEVEL_DBG=y \
-DCONFIG_NET_SHELL=y -DCONFIG_NET_LOG=y

[learnerr2024]

Thanks for your help! I am beginning in this field

I dont have any real device so I tried to emulate a smart bulb seeking reference from this link:https://docs.zephyrproject.org/latest/samples/net/sockets/http_server/README.html

[jukkar]

Could you adjust the code / log output text in the comments to make it readable (now it is hard to read), you need to use triple backticks (and placing them in separate lines). Use the preview button to verify that things look ok. I adjusted the initial message but the latter one has too much stuff going on.

[jukkar]

Your comments are difficult to read because of lack of proper formatting.
What I would suggest to you is take the samples/net/sockets/http_server sample as a base and then adjust it by removing things that you do not need, and adding new stuff that you need. The http_server sample with qemu supports also TAP if you want to use it, other alternative is using normal Ethernet interface zeth which works with native-sim and Qemu. Instructions how to do use the interfaces can be found in the documentation (I had it linked somewhere above).

[learnerr2024]

Hello! I don't have any real device and i am beginner in this area!

I am facing this error::
output:
-- west build: running target run

[0/1] To exit from QEMU enter: 'CTRL+a, x'[QEMU] CPU: qemu32,+nx,+pae
SeaBIOS (version zephyr-v1.0.0-0-g31d4e0e-dirty-20200714_234759-fv-az50-zephyr)
Booting from ROM..
*** Booting Zephyr OS build v4.0.0-rc1-22-g14478cafa6a4 ***
[00:00:00.020,000] net_sock_tls: No entropy device on the system, TLS communication is insecure!
[00:00:00.020,000] net_config: Initializing network
[00:00:00.020,000] net_config: IPv4 address: 192.0.2.1
[00:00:00.120,000] net_config: IPv6 address: 2001:db8::1
[00:00:00.120,000] net_config: IPv6 address: 2001:db8::1
[00:00:00.120,000] smart_bulb_emulator: TLS setup completed
[00:00:00.120,000] net_http_server: All services failed (0)
[00:00:00.120,000] net_http_server: Failed to initialize HTTP2 server
[00:00:00.120,000] net_http_server: Re-starting server (-3)
[00:00:01.130,000] net_http_server: All services failed (0)
[00:00:01.130,000] net_http_server: Failed to initialize HTTP2 server
[00:00:01.130,000] net_http_server: Re-starting server (-3)
[00:00:02.140,000] net_http_server: All services failed (0)
[00:00:02.140,000] net_http_server: Failed to initialize HTTP2 server
[00:00:02.140,000] net_http_server: Re-starting server (-3)
uart:~$ qemu-system-i386: terminating on signal 2

what changes should i make in prj.conf to solve this error.
prj.conf
prj.conf:
General Configuration
CONFIG_MAIN_STACK_SIZE=3072
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048
CONFIG_SHELL=y
CONFIG_LOG=y
CONFIG_ENTROPY_GENERATOR=y
CONFIG_TEST_RANDOM_GENERATOR=y
CONFIG_INIT_STACKS=y
CONFIG_ZVFS_OPEN_MAX=32
CONFIG_POSIX_API=y
CONFIG_FDTABLE=y
CONFIG_ZVFS_POLL_MAX=32
CONFIG_EVENTFD=y
CONFIG_NETWORKING=y
CONFIG_NET_IPV4=y
CONFIG_NET_IPV6=y
CONFIG_NET_TCP=y
CONFIG_NET_SOCKETS=y
CONFIG_NET_CONNECTION_MANAGER=y
CONFIG_NET_SHELL=y
CONFIG_NET_STATISTICS=y
CONFIG_NET_STATISTICS_USER_API=y
CONFIG_NET_LOG=y
CONFIG_JSON_LIBRARY=y
CONFIG_HTTP_PARSER_URL=y
CONFIG_HTTP_PARSER=y
CONFIG_HTTP_SERVER=y
CONFIG_HTTP_SERVER_WEBSOCKET=y
CONFIG_NET_PKT_RX_COUNT=16
CONFIG_NET_PKT_TX_COUNT=16
CONFIG_NET_BUF_RX_COUNT=128
CONFIG_NET_BUF_TX_COUNT=128
CONFIG_NET_CONTEXT_NET_PKT_POOL=y
CONFIG_NET_IF_UNICAST_IPV6_ADDR_COUNT=3
CONFIG_NET_IF_MCAST_IPV6_ADDR_COUNT=4
CONFIG_NET_MAX_CONTEXTS=32
CONFIG_NET_MAX_CONN=32
CONFIG_NET_CONFIG_SETTINGS=y
CONFIG_NET_CONFIG_NEED_IPV4=y
CONFIG_NET_CONFIG_NEED_IPV6=y
CONFIG_NET_CONFIG_MY_IPV4_ADDR="192.0.2.1"
CONFIG_NET_CONFIG_PEER_IPV4_ADDR="192.0.2.2"
CONFIG_NET_CONFIG_MY_IPV4_GW="192.0.2.2"
CONFIG_NET_CONFIG_MY_IPV6_ADDR="2001:db8::1"
CONFIG_NET_CONFIG_PEER_IPV6_ADDR="2001:db8::2"
CONFIG_MBEDTLS=y
CONFIG_MBEDTLS_BUILTIN=y
CONFIG_MBEDTLS_ENABLE_HEAP=y
CONFIG_MBEDTLS_HEAP_SIZE=60000
CONFIG_MBEDTLS_SSL_MAX_CONTENT_LEN=2048
CONFIG_MBEDTLS_USE_PSA_CRYPTO=n
CONFIG_NET_SOCKETS_SOCKOPT_TLS=y
CONFIG_NET_SOCKETS_TLS_MAX_CONTEXTS=6
CONFIG_TLS_CREDENTIALS=y
CONFIG_TLS_MAX_CREDENTIALS_NUMBER=5
CONFIG_NET_TCP_TIME_WAIT_DELAY=0
CONFIG_GPIO=n
CONFIG_LED=n
CONFIG_NET_SOCKETS_LOG_LEVEL_DBG=n
CONFIG_NET_HTTP_LOG_LEVEL_DBG=n
CONFIG_NET_IPV6_LOG_LEVEL_DBG=n
CONFIG_NET_IPV6_ND_LOG_LEVEL_DBG=n

[rlubos]

Have you tried out the samples/net/sockets/http_server as suggested by @jukkar? It works out of the box with qemu_x86.

[00:00:00.120,000] net_http_server: All services failed (0)
[00:00:00.120,000] net_http_server: Failed to initialize HTTP2 server

This looks as if no HTTP services were defined, please check the sample code:
https://github.com/zephyrproject-rtos/zephyr/blob/main/samples/net/sockets/http_server/src/main.c#L250