The only standard tools that support SIGINFO are sleep, dd and ping, (and kill, for obvious reasons) so it's not like there's a vast hole in the tooling or something, nor is there a large legacy software base just waiting for SIGINFO to appear. So while I very much enjoyed figuring out how to make SIGINFO work ... I'll have the VSTATUS patch out in a little bit. I also think there might be some merit in consolidating the 10 'sigsetsize != sizeof(sigset_t)' checks in a macro and adding comments that wave people off on trying to do what I did. If that would be useful, happy to provide the patch. On Tue, Jan 4, 2022 at 2:23 PM Theodore Ts'o <tytso@xxxxxxx> wrote: > > On Tue, Jan 04, 2022 at 04:05:26PM -0600, Eric W. Biederman wrote: > > > > That is all as expected, and does not demonstrate a regression would > > happen if SIGPWR were to treat SIG_DFL as SIG_IGN, as SIGWINCH, SIGCONT, > > SIGCHLD, SIGURG do. It does show there is the possibility of problems. > > > > The practical question is does anything send SIGPWR to anything besides > > init, and expect the process to handle SIGPWR or terminate? > > So if I *cared* about SIGINFO, what I'd do is ask the systemd > developers and users list if there are any users of the sigpwr.target > feature that they know of. And I'd also download all of the open > source UPS monitoring applications (and perhaps documentation of > closed-source UPS applications, such as for example APC's program) and > see if any of them are trying to send the SIGPWR signal. > > I don't personally think it's worth the effort to do that research, > but maybe other people care enough to do the work. > > > > I claim, though, that we could implement VSTATUS without implenting > > > the SIGINFO part of the feature. > > > > I agree that is the place to start. And if we aren't going to use > > SIGINFO perhaps we could have an equally good notification method > > if anyone wants one. Say call an ioctl and get an fd that can > > be read when a VSTATUS request comes in. > > > > SIGINFO vs SIGCONT vs a fd vs something else is something we can sort > > out when people get interested in modifying userspace. > > > Once VSTATUS support lands in the kernel, we can wait and see if there > is anyone who shows up wanting the SIGINFO functionality. Certainly > we have no shortage of userspace notification interfaces in Linux. :-) > > - Ted
