kqueue(2) already supports EVFILT_PROC. Add an EVFILT_PROCDESC that
behaves the same, but operates on a procdesc(4) instead. Only implement
NOTE_EXIT for now. The nice thing about NOTE_EXIT is that it also
returns the exit status of the process, meaning that we can now obtain
this value, even if pdwait4(2) is still unimplemented.
Notes:
- Simply reuse EVFILT_NETDEV for EVFILT_PROCDESC. As both of these will
be used on totally different descriptor types, this should not clash.
- Let procdesc_kqops_event() reuse the same structure as filt_proc().
The only difference is that procdesc_kqops_event() should also be able
to deal with the case where the process was already terminated after
registration. Simply test this when hint == 0.
- Fix some style(9) issues in filt_proc() to keep it consistent with the
newly added procdesc_kqops_event().
- Save the exit status of the process in pd->pd_xstat, as we cannot pick
up the proctree_lock from within procdesc_kqops_event().
Discussed on: arch@
Reviewed by: kib@
The pdfork(2) man page states:
"pdfork() returns a PID, 0 or -1, as fork(2) does."
As it returns a PID, the return type should obviously be pid_t. As int
and pid_t have the same size on all architectures, this change does not
affect the ABI in any way.
requires process descriptors to work and having PROCDESC in GENERIC
seems not enough, especially that we hope to have more and more consumers
in the base.
MFC after: 3 days
A "process descriptor" file descriptor is used to manage processes
without using the PID namespace. This is required for Capsicum's
Capability Mode, where the PID namespace is unavailable.
New system calls pdfork(2) and pdkill(2) offer the functional equivalents
of fork(2) and kill(2). pdgetpid(2) allows querying the PID of the remote
process for debugging purposes. The currently-unimplemented pdwait(2) will,
in the future, allow querying rusage/exit status. In the interim, poll(2)
may be used to check (and wait for) process termination.
When a process is referenced by a process descriptor, it does not issue
SIGCHLD to the parent, making it suitable for use in libraries---a common
scenario when using library compartmentalisation from within large
applications (such as web browsers). Some observers may note a similarity
to Mach task ports; process descriptors provide a subset of this behaviour,
but in a UNIX style.
This feature is enabled by "options PROCDESC", but as with several other
Capsicum kernel features, is not enabled by default in GENERIC 9.0.
Reviewed by: jhb, kib
Approved by: re (kib), mentor (rwatson)
Sponsored by: Google Inc
