When capsicum was originally integrated into FreeBSD, a placeholder syscall (pdwait4(2)) was added, but not completed. This is an enhancement bug/reminder for interested parties to implement the syscall. More information about this can be found in https://reviews.freebsd.org/D18950 .
linimon: a patch to implement the syscall hasn't been provided yet, so I'm going to remove the keyword (to avoid misleading end-users).
A commit references this bug: Author: ngie Date: Thu Feb 28 18:12:15 UTC 2019 New revision: 344662 URL: https://svnweb.freebsd.org/changeset/base/344662 Log: Remove references to pdwait4(2) and `CAP_PDWAIT` from rights(4) @cem removed references to pdwait4(2) (a nonexistent syscall) in r320058. This change removes references to pdwait4(2) and `CAP_PDWAIT` in rights(4) to not mislead the user into thinking that pdwait4(2)/`CAP_PDWAIT` is actually implemented in the stock FreeBSD kernel. The goal of this functionality was to simplify monitoring/manipulating processes started with `pdfork`, et al, and avoid races with waiting on pids. The syscall was never completed though--just discussed on the capsicum mailing list back in 2015: https://lists.cam.ac.uk/pipermail/cl-capsicum-discuss/2015-May/msg00012.html . That being said, there are members of the project (@rwatson, etc) who have longterm goals to implement this syscall to better secure pdfork(2) calls. PR: 235871 Reviewed by: emaste Discussed with: rwatson Approved by: emaste (mentor) MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D18950 Changes: head/share/man/man4/rights.4 head/sys/sys/capsicum.h
A commit references this bug: Author: ngie Date: Tue Apr 9 16:35:24 UTC 2019 New revision: 346059 URL: https://svnweb.freebsd.org/changeset/base/346059 Log: MFC r344662: Remove references to pdwait4(2) and `CAP_PDWAIT` from rights(4) @cem removed references to pdwait4(2) (a nonexistent syscall) in r320058. This change removes references to pdwait4(2) and `CAP_PDWAIT` in rights(4) to not mislead the user into thinking that pdwait4(2)/`CAP_PDWAIT` is actually implemented in the stock FreeBSD kernel. The goal of this functionality was to simplify monitoring/manipulating processes started with `pdfork`, et al, and avoid races with waiting on pids. The syscall was never completed though--just discussed on the capsicum mailing list back in 2015: https://lists.cam.ac.uk/pipermail/cl-capsicum-discuss/2015-May/msg00012.html . That being said, there are members of the project (@rwatson, etc) who have longterm goals to implement this syscall to better secure pdfork(2) calls. PR: 235871 Approved by: emaste (mentor) Differential Revision: https://reviews.freebsd.org/D19805 Changes: stable/12/share/man/man4/rights.4 stable/12/sys/sys/capsicum.h