On 11.03.2018 17:25, Robert Elz wrote: > Date: Sun, 11 Mar 2018 16:02:57 +0100 > From: Kamil Rytarowski <n...@gmx.com> > Message-ID: <10b0efe2-35bb-d1e8-ed28-587f643bd...@gmx.com> > > | POSIX people told me that polling of a process entity is reliable only > | for parent (whether a real one or a tracer in non-POSIX extensions). > > I agree with that - what's more, that is all it reasonably can be. > > | We can use pid lookup in this particular case calling proc_find_raw(). > > Yes, there's an XXX comment in the code already, but I agree: > > | I treat this as just an optimization (something nice to have, but not > | important now). > > An alternative would be to simply break out of the loop after having > found the process in the case of (op == KERN_PROC_PID) > > | This will not solve the bug for other sysctl_doeproc() cases and a fix > | is still needed. > > Is it really? Those cases won't have the issue you saw of there > being insufficient buffer space (or the code will handle that already) > as the number of processes that match could be anything, the buffer > will not (should not) have space for just one (unlike the KERN_PROC_PID > case where only 1 should be possible). >
I consider the status of two processes (alive and zombie) returned at once as a bug and non-logical snapshot of the list of processes. POSIX specifies lifetime of a process and it's either alive or zombie, not both. There is a lack of specification what happens in between: Process: "A live process (see Live Process) or a zombie process (see Zombie Process )." I expect an interface like sysctl(3) to get a quick snapshot of the current system, and an observation of 0 or 1 makes sense to me, while 2 does not. We are not cloning a process and making the clone a zomie, and killing the living one. We could get a list of duplicates for KERN_PROC_PGRP, KERN_PROC_SESSION etc. I don't think that KERN_PROC_PID is fundamentally different. Assuming that a process died and is invisible, before becoming a zombie is a good [to me] metaphor. We could also return ESRCH for 0 detected results to make handling of this case easier and repeat the polling function. Regarding short-circuit, if we want to go this route now, I propose to go immediately to proc_find_raw() and make it O(1) instead of O(n). I will prepare a patch once we will agree whether to return 0-1 or 1-2 entries for a single process. > | We already use markers so I prefer to stick to this solution and it > | makes this code reliable. > > I don't much like the way you LIST_REMOVE(marker0) - if we add almost > any fix to short circuit the complete list scan after having found the proc > entry for the KERN_PROC_PID case your current method will fail. > > Better to simply remove it after the loop ends (no matter why it ends), > rather than when it is used (and then also do it in the cleanup code > always, rather than only when !mmmbrains). That's simpler, and easier > to understand. > OK!
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