6dd333dfe
Denis Vlasenko
2007-08-25
Subject
Start a small document "why ifupdown is bad"
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docs/ifupdown_design.txt+44 -0
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| + | This document is meant to convince you to not use ifup/ifdown. |
| + | |
| + | |
| + | The general problem with ifupdown is that it is "copulated in vertical |
| + | fashion" by design. It tries to do the job of shell script in C, |
| + | and this is invariably doomed to fail. You need ifup/ifdown |
| + | to be adaptable by local admins, and C is an extremely poor choice |
| + | for that. |
| + | |
| + | We are doomed to have problems with ifup/ifdown. Just look as this code: |
| + | |
| + | static const struct dhcp_client_t ext_dhcp_clients[] = { |
| + | { "dhcpcd", "<up cmd>", "<down cmd>" }, |
| + | { "dhclient", ........ }, |
| + | { "pump", ........ }, |
| + | { "udhcpc", ........ }, |
| + | }; |
| + | |
| + | static int dhcp_down(struct interface_defn_t *ifd, execfn *exec) |
| + | { |
| + | #if ENABLE_FEATURE_IFUPDOWN_EXTERNAL_DHCP |
| + | int i ; |
| + | for (i = 0; i < ARRAY_SIZE(ext_dhcp_clients); i++) { |
| + | if (exists_execable(ext_dhcp_clients[i].name)) |
| + | return execute(ext_dhcp_clients[i].stopcmd, ifd, exec); |
| + | } |
| + | bb_error_msg("no dhcp clients found, using static interface shutdown"); |
| + | return static_down(ifd, exec); |
| + | #elif ENABLE_APP_UDHCPC |
| + | return execute("kill " |
| + | "`cat /var/run/udhcpc.%iface%.pid` 2>/dev/null", ifd, exec); |
| + | #else |
| + | return 0; /* no dhcp support */ |
| + | #endif |
| + | } |
| + | |
| + | How the hell it is supposed to work reliably this way? Just imagine that |
| + | admin is using pump and ifup/ifdown. It works. Then, for whatever reason, |
| + | admin installs dhclient, but does NOT use it. ifdown will STOP WORKING, |
| + | just because it will see installed dhclient binary in e.g. /usr/bin/dhclient! |
| + | This is stupid. |
| + | |
| + | I seriously urge people to not use ifup/ifdown. |
| + | Use something less brain damaged. |