NAME
pdfork, pdgetpid,
pdkill —
System calls to manage process
descriptors
LIBRARY
library “libc”
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 usingpdfork(),
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 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.
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_PDKILLforpdkill()).
SEE ALSO
close(2), fork(2), fstat(2), kill(2), poll(2), kqueue(2), wait4(2), capsicum(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.