catch-22 VTY error

I'd like to share a VTY config error analysis that has a tricky solution: I started osmo-bsc -c osmo-bsc.cfg with, according to openbsc/doc/examples/osmo-bsc: net [...] bts 0 [...] periodic location update 30 trx 0 [...] and get this error: There is no such command. Error occurred during reading below line: trx 0 what? 'net / bts / trx' is no command?? Solution: I'm on the vlr_3G branch (incorporating 2G via A-interface) and on this branch, I've actually moved the 'periodic location update N' command a level up, from net / bts / periodic to net / periodic (background: assuming that OsmoMSC does not have individual BTS info, we moved some settings up to network level; whether this makes sense for osmo-bsc is a different question, it's just what happens to be on the vlr_3G branch now). So there is no net / bts / periodic command. Why do I get an error for net / bts / trx instead? two reasons: 1. 'trx 0' was the line following the 'periodic' command, 2. since 'periodic' exists one level above, the vty code goes to the parent node automatically. About 2: we tend to indent our VTY config files, but in fact the indentation has no effect whatsoever, it is just eye candy (very useful eye candy). The code in question: If a command does not exist, try 'vty_go_parent()' and see if the command exists there. That's what allows us to omit 'exit' in our config files to go to the parent node explicitly: libosmocore/src/vty/command.c: int config_from_file(struct vty *vty, FILE * fp) { int ret; vector vline; while (fgets(vty->buf, VTY_BUFSIZ, fp)) { vline = cmd_make_strvec(vty->buf); /* In case of comment line */ if (vline == NULL) continue; /* Execute configuration command : this is strict match */ ret = cmd_execute_command_strict(vline, vty, NULL); /* Try again with setting node to CONFIG_NODE */ while (ret != CMD_SUCCESS && ret != CMD_WARNING && ret != CMD_ERR_NOTHING_TODO && is_config_child(vty)) { HERE -----> vty_go_parent(vty); ret = cmd_execute_command_strict(vline, vty, NULL); } cmd_free_strvec(vline); if (ret != CMD_SUCCESS && ret != CMD_WARNING && ret != CMD_ERR_NOTHING_TODO) return ret; } return CMD_SUCCESS; } In this case the 'periodic...' command does in fact now exist one level above, so the vty_go_parent() is successful and running that command works. But, the vty config parsing then sits above on the 'network' level, is no longer in 'bts 0' and hence refuses to accept the following bts-level command, in this case 'trx 0'. Confusing! So it's not a bug, it's a feature. But it's a feature we might see quite often if we move the 'periodic' command up to network level and users attempt to use their old config files. Same goes for the 'timezone' command, BTW, so we might want to rename commands, or re-consider moving commands one level up in the first place. Maybe we should leave backward compat catchers in place that print a warning. ~N -- - Neels Hofmeyr <nhofmeyr(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschäftsführer / Managing Directors: Harald Welte