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PDFORK(2)		       System Calls Manual		       PDFORK(2)

NAME
     pdfork, pdgetpid, pdkill -- System calls to manage process descriptors

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/procdesc.h>

     pid_t
     pdfork(int *fdp, int flags);

     int
     pdgetpid(int fd, pid_t *pidp);

     int
     pdkill(int fd, int signum);

DESCRIPTION
     Process  descriptors are special file descriptors that represent processes,
     and are created using pdfork(), a variant of fork(2), which, if successful,
     returns a process descriptor in the integer pointed to by	fdp.   Processes
     created  via  pdfork() will not cause SIGCHLD on termination.  pdfork() can
     accept the flags:

     PD_DAEMON	Instead of the default terminate-on-close behaviour,  allow  the
		process to live until it is explicitly killed with kill(2).

		This option is not permitted in capsicum(4) capability mode (see
		cap_enter(2)).

     PD_CLOEXEC
		Set close-on-exec on process descriptor.

     pdgetpid() queries the process ID (PID) in the process descriptor fd.

     pdkill()  is  functionally  identical  to kill(2), except that it accepts a
     process descriptor, fd, rather than a PID.

     The following system calls also have effects specific to  process	descrip-
     tors:

     fstat(2)  queries	status	of  a  process	descriptor;  currently	only the
     st_mode, st_birthtime, st_atime, st_ctime and st_mtime fields are	defined.
     If  the owner read, write, and execute bits are set then the process repre-
     sented by the process descriptor is still alive.

     poll(2) and select(2) allow waiting for  process  state  transitions;  cur-
     rently  only  POLLHUP is defined, and will be raised when the process dies.
     Process state transitions can also  be  monitored	using  kqueue(2)  filter
     EVFILT_PROCDESC; currently only NOTE_EXIT is implemented.

     close(2)  will close the process descriptor unless PD_DAEMON is set; if the
     process is still alive and this is the last reference to  the  process  de-
     scriptor, the process will be terminated with the signal SIGKILL.

RETURN VALUES
     pdfork() returns a PID, 0 or -1, as fork(2) does.

     pdgetpid() and pdkill() return 0 on success and -1 on failure.

ERRORS
     These functions may return the same error numbers as their PID-based equiv-
     alents  (e.g.  pdfork() may return the same error numbers as fork(2)), with
     the following additions:

     [EINVAL]		The signal number given to pdkill() is invalid.

     [ENOTCAPABLE]	The process descriptor being operated  on  has	insuffi-
			cient rights (e.g.  CAP_PDKILL for pdkill()).

SEE ALSO
     close(2),	fork(2),  fstat(2),  kill(2), kqueue(2), poll(2), wait4(2), cap-
     sicum(4), procdesc(4)

HISTORY
     The pdfork(), pdgetpid(), and  pdkill()  system  calls  first  appeared  in
     FreeBSD 9.0.

     Support  for  process  descriptors  mode  was  developed  as  part  of  the
     TrustedBSD Project.

AUTHORS
     These functions and the capability facility were created by  Robert  N.  M.
     Watson  <rwatson@FreeBSD.org>  and Jonathan Anderson <jonathan@FreeBSD.org>
     at the University of Cambridge Computer  Laboratory  with	support  from  a
     grant from Google, Inc.

FreeBSD 15.0			October 14, 2018		       PDFORK(2)
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