On 7/30/19 11:19 AM, Greg Kroah-Hartman wrote: > 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? People were lamenting the lack of siginfo in linux back in May, I offered to try to implement it, several people jumped in to offer suggestions, and it turns out you can't really do it without kernel support. https://twitter.com/landley/status/1131764323196522498 >> 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. I couldn't figure out how to do it without kernel support when I tried. http://lists.landley.net/pipermail/toybox-landley.net/2019-May/010461.html Rob
