NAME

       pdfork, pdgetpid, pdkill, pdwait4 — 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);

       int
       pdwait4(int fd, int *status, int options, struct rusage *rusage);

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.

       pdwait4()  behaves  identically  to  wait4(2), but operates with respect to a process descriptor argument
       rather than a PID.

       The following system calls also have effects specific to process descriptors:

       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 represented by the process descriptor is still alive.

       poll(2) and select(2) allow waiting for process state transitions; currently 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 descriptor, 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.

       pdwait4() returns a PID on success and -1 on failure.

ERRORS

       These  functions  may  return  the  same error numbers as their PID-based equivalents (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 insufficient rights (e.g.  CAP_PDKILL for
                          pdkill()).

SEE ALSO

       close(2), fork(2), fstat(2), kill(2), poll(2), wait4(2), capsicum(4), procdesc(4)

HISTORY

       The pdfork(), pdgetpid(), pdkill() and pdwait4() 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.

BUGS

       pdwait4() has not yet been implemented.

Debian                                            June 8, 2016                                         PDFORK(2)