Commit Graph

4 Commits

Author SHA1 Message Date
Nicholas J. Kain
a9874d4959 Support running an executable file when a new lease is acquired.
If no 'script-file = SCRIPTFILE' is specified in the configuration
file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE'
command argument is provided, then this functionality is entirely
inactive and no associated subprocess is spawned.

Otherwise, ndhc will spawn a subprocess that runs as root that has the
sole job of forking off a subprocess that exec's the specified script in
a sanitized and fixed-state environment whenever a new DHCPv4 lease is
acquired.

Note that this script is provided no information about ndhc or the
DHCP state in the environment or in any argument fields; it is the
responsibility of this script to gather whatever information it needs
from either the filesystem or syscalls.  This design is intended to
avoid the historical problems that are associated with dhcp clients
invoking scripts.

The path of the scriptfile cannot be changed after ndhc is initially
run; ndhc forks off the privsep script subprocess that executes scripts
after it has read the configuration file and command arguments, but
before it begins processing network data; thus, it is impossible for the
network-handling process to modify or influence the script assuming
proper OS memory protection.

The privsep channel communicates that the script should be run by simply
writing a newline; anything else will result in ndhc terminating itself.

Before the recommended way to update system state after a change in
lease information was to run the fcactus program and watch the
associated leasefile for the interface for modification; now no external
program is needed for this job.
2022-02-24 03:58:37 -05:00
Nicholas J. Kain
2fb16567f1 Support s6 service startup notification
This can be enabled via the s6-notify configure option; see
http://www.skarnet.org/software/s6/notifywhenup.html for details.

ndhc will signal that it is ready when the first valid lease is
obtained.  Programs dependent on a working network interface
can then simply use s6-wait on the associated ndhc service dir.

A typical command line option assuming the s6 service directory
notification-fd contains '3' would be '--s6-notify 3', and
a typical configure file option would be 's6-notify 3'.
2022-02-13 05:25:17 -05:00
Nicholas J. Kain
1732bccccc Relicense as MIT.
It's a lot more common than BSD 2-clause it is both compatible
and nearly identical in effect.
2022-02-06 20:05:29 -05:00
Nicholas J. Kain
8db8c5589d Replace CMake with GNU Make.
There was previously support for both build systems, but ndhc is
undemanding and there is no point in maintaining a complex
CMake build.
2022-01-22 18:39:41 -05:00