mirror of
https://github.com/vdsm/virtual-dsm.git
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84 lines
2.3 KiB
Python
Executable File
84 lines
2.3 KiB
Python
Executable File
#!/usr/bin/env python3
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import argparse
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import ipaddress
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import json
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import re
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import subprocess
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from typing import List
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DEFAULT_ROUTE = "default"
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NS_IP_RE = re.compile(r'^nameserver\s+(\S+)$')
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RESOLV_CONF_PATH = '/etc/resolv.conf'
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DHCP_CONF_TEMPLATE = """
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start {host_addr}
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end {host_addr}
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# avoid dhcpd complaining that we have
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# too many addresses
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maxleases 1
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interface {dhcp_intf}
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option dns {dns}
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option router {gateway}
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option subnet {subnet}
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"""
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def nameservers() -> List[str]:
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"""Returns the list of nameserver IPs in resolv.conf"""
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result = []
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with open(RESOLV_CONF_PATH) as resolv_f:
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for line in resolv_f:
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match = NS_IP_RE.match(line)
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if match:
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result.append(match.group(1))
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return result
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def default_route(routes):
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"""Returns the host's default route"""
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for route in routes:
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if route['dst'] == DEFAULT_ROUTE:
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return route
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raise ValueError('no default route')
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def addr_of(addrs, dev : str) -> ipaddress.IPv4Interface:
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"""Finds and returns the IP address of `dev`"""
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for addr in addrs:
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if addr['ifname'] != dev:
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continue
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if len(addr['addr_info']) != 1:
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raise ValueError('only exactly one address on dev is supported')
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info = addr['addr_info'][0]
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return ipaddress.IPv4Interface((info['local'], info['prefixlen']))
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raise ValueError('dev {0} not found'.format(dev))
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def generate_conf(intf_name : str) -> str:
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"""Generates a dhcpd config. `intf_name` is the interface to listen on."""
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with subprocess.Popen(['ip', '-json', 'route'],
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stdout=subprocess.PIPE) as proc:
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routes = json.load(proc.stdout)
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with subprocess.Popen(['ip', '-json', 'addr'],
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stdout=subprocess.PIPE) as proc:
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addrs = json.load(proc.stdout)
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droute = default_route(routes)
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host_addr = addr_of(addrs, droute['dev'])
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return DHCP_CONF_TEMPLATE.format(
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dhcp_intf = intf_name,
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dns = ' '.join(nameservers()),
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host_addr = host_addr.ip,
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gateway = droute['gateway'],
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subnet = host_addr.network.netmask,
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)
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if __name__ == '__main__':
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parser = argparse.ArgumentParser()
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parser.add_argument('intf_name')
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args = parser.parse_args()
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print(generate_conf(args.intf_name))
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