LXC attach exit on SIGCHLD, corrections

[asainkujovic]

These corrections resolve all mentioned regressions from reverting-commit

I have also prepared possible branches (1) and (2) for introducing the suggested new cmd-line-parameter, but this version still remains significantly cleaner and easier to understand.

[hallyn]

iiuc it doesn't address @mihalicyn 's 4th point, that this changes the API. So i think one of your other branches is required.

[asainkujovic]

@hallyn hi just to mention now when changes are reviewed again, as far as i remember API should stay the same, and program behavior differs only when LXC_ATTACH_TERMINAL flag explicitly turned ON (by default is OFF). Currently it is only used as ON inside lxc_attach.c (lxc_attach program itself where we need the change). And other callers of the API will be affected only if they for some reason attaches terminal too, and if they are setting this flag (where again they probably need the change to, but you know better from experience)

[mihalicyn]

@hallyn hi just to mention now when changes are reviewed again, as far as i remember API should stay the same, and program behavior differs only when LXC_ATTACH_TERMINAL flag explicitly turned ON (by default is OFF). Currently it is only used as ON inside lxc_attach.c (lxc_attach program itself where we need the change). And other callers of the API will be affected only if they for some reason attaches terminal too, and if they are setting this flag (where again they probably need the change to, but you know better from experience)

Hi @asainkujovic,

I don't want to be picky, but actually, if any LXC command changes it's behavior then it's also API change, it is not a liblxc API change, but it's LXC API change. We don't even know in how many places and how LXC command line utilities are used - bash scripts, Python projects, autopkgtests in Debian. I'm afraid to break stuff for so many different projects consuming LXC. It's better to have a new command line parameter and do everything in the most compatible way, IMHO.

Kind regards,
Alex