On 03/12/2015 04:32 PM, Harald Becker wrote:
On 12.03.2015 19:38, Michael Conrad wrote:
On 3/12/2015 12:04 PM, Harald Becker wrote:
but that one will only work when you either use the kernel hotplug
helper mechanism, or the netlink approach. You drop out those who
can't / doesn't want to use either.
...which I really do think could be answered in one paragraph :-) If the
netlink socket is the "right way" to solve the forkbomb problem that
happens with hotplug helpers, then why would anyone want to solve it the
wrong way? I don't understand the need.
To clarify,
1 - kernel-spawned hotplug helpers is the traditional way,
2 - netlink socket daemon is the "right way to solve the forkbomb
problem"
3 - kernel-spawned fifo-writer, with fifo read by hotplug daemon is
"solve it the wrong way".
ohh, good question! ... ask Isaac! (answer in one paragraph?)
What I hear Isaac say is "leave #1 (traditional way) alone. I want to
keep using it".
I agree with him that it should stay. But I would choose to use #2 if
it were available. I am asking the purpose of #3.
Conclusion: As I accept different preferences, and I do not want to
force others more than possible, I tried to find a solution which
allows every required mechanism (with maximum code sharing), and let
the user chose which one to use. In addition BB has a config system
which allows to disable unwanted stuff, so you can opt out the hotplug
stuff when you like.
So I think your answer to my original question is "the fifo design is a
way to have #1 and #2 without duplicating code".
In that case, I would offer this idea:
1. Refactor mdev to look like this: (pseudocode)
mdev_main() {
read_options();
load_config();
process_request(); // from environment variables
}
2. Add the following:
mdev_main() {
read_options();
load_config();
#ifdef FEATURE_MDEV_NETLINK
if (option_netlink) {
open_netlink_socket();
while (recv(message)) {
apply_env_from_message(message);
process_request();
}
}
else
#endif
process_request();
}
3. Then to support the ability to launch mdev connected to a netlink
socket that already exists, and time out when not used,
mdev_main() {
read_options();
load_config();
#ifdef FEATURE_MDEV_NETLINK
if (option_netlink) {
if (!option_netlink_on_stdin) {
close(0);
open_netlink_socket();
}
while (select([0], timeout)) {
if (recv(0, message)) {
apply_env_from_message(message);
process_request();
}
}
}
else
#endif
process_request();
}
I think this will be even smaller than what you propose with the fifo.
It will do netlink, it will do the traditional hotplug helper, and even
allow the trick where a tiny daemon monitors netlink and can start mdev
in daemon mode on demand.
-Mike
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