On Tue, Jun 25, 2019 at 07:11:53PM +0300, Arseny Maslennikov wrote: > If the three termios local flags isig, icanon, iexten are enabled > and the local flag nokerninfo is disabled for a tty governed > by the n_tty line discipline, then on receiving the keyboard status > character n_tty will generate a status message and write it out to > the tty before sending SIGINFO to the tty's foreground process group. > > This kerninfo line contains information about the current system load > as well as some properties of "the most interesting" process in the > tty's current foreground process group, namely: > - its PID as seen inside its deepest PID namespace; > * the whole process group ought to be in a single PID namespace, > so this is actually deterministic > - its saved command name truncated to 16 bytes (task_struct::comm); > * at the time of writing TASK_COMM_LEN == 16 > - its state and some related bits, procps-style; > - for S and D: its symbolic wait channel, if available; or a short > description for other process states instead; > - its user, system and real rusage time values; > - its resident set size (as well as the high watermark) in kilobytes. Why is this really all needed as we have the SysRq handlers that report all of this today? > The "most interesting" process is chosen as follows: > - runnables over everything > - uninterruptibles over everything else > - among 2 runnables pick the biggest utime + stime > - any unresolved ties are decided in favour of greatest PID. This does not feel like something that the tty core code should be doing at all. > While the kerninfo line is not very useful for debugging the kernel > itself, since we have much more powerful debugging tools, it still gives > the user behind the terminal some meaningful feedback to a VSTATUS that > works even if no processes respond. That's what SysRq is for. If there's a specific set of values that we don't currently report in that facility, why not just add the information there? It's much simpler and "safer" that way. thanks, greg k-h
