libc/sys/procctl.2

    procctl.2 revision 276686
     Copyright (c) 2013 Advanced Computing Technologies LLC
 Written by: John H. Baldwin <jhb@FreeBSD.org>
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 Copyright (c) 2014 The FreeBSD Foundation
 Portions of this documentation were written by Konstantin Belousov
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 $FreeBSD: stable/10/lib/libc/sys/procctl.2 276686 2015-01-05 03:27:09Z kib $

.Dd December 16, 2014
.Dt PROCCTL 2
.Os
.Sh NAME
.Nm procctl
.Nd control processes
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
n sys/procctl.h .Ft int
.Fn procctl "idtype_t idtype" "id_t id" "int cmd" "void *arg"
.Sh DESCRIPTION
The
.Fn procctl
system call provides for control over processes.
The
.Fa idtype
and
.Fa id
arguments specify the set of processes to control.
If multiple processes match the identifier,
.Nm
will make a
.Dq best effort
to control as many of the selected processes as possible.
An error is only returned if no selected processes successfully complete
the request.
The following identifier types are supported:
l -tag -width "Dv P_PGID" t Dv P_PID Control the process with the process ID
.Fa id .
t Dv P_PGID Control processes belonging to the process group with the ID
.Fa id .
.El
p
The control request to perform is specified by the
.Fa cmd
argument.
The following commands are supported:
l -tag -width "Dv PROC_REAP_GETPIDS" t Dv PROC_SPROTECT Set process protection state.
This is used to mark a process as protected from being killed if the system
exhausts available memory and swap.
The
.Fa arg
parameter must point to an integer containing an operation and zero or more
optional flags.
The following operations are supported:
l -tag -width "Dv PPROT_CLEAR" t Dv PPROT_SET Mark the selected processes as protected.
t Dv PPROT_CLEAR Clear the protected state of selected processes.
.El
p
The following optional flags are supported:
l -tag -width "Dv PPROT_DESCE" t Dv PPROT_DESCEND Apply the requested operation to all child processes of each selected process
in addition to each selected process.
t Dv PPROT_INHERIT When used with
.Dv PPROT_SET ,
mark all future child processes of each selected process as protected.
Future child processes will also mark all of their future child processes.
.El
t Dv PROC_REAP_ACQUIRE Acquires the reaper status for the current process.
The status means that children orphaned by the reaper's descendants
that were forked after the acquisition of the status are reparented to the
reaper.
After the system initialization,
.Xr init 8
is the default reaper.
p
t Dv PROC_REAP_RELEASE Releases the reaper state for the current process.
The reaper of the current process becomes the new reaper of the
current process's descendants.
t Dv PROC_REAP_STATUS Provides the information about the reaper of the specified process,
or the process itself when it is a reaper.
The
.Fa data
argument must point to a
.Vt procctl_reaper_status
structure which is filled in by the syscall on successful return.
d -literal struct procctl_reaper_status {
 u_int rs_flags;
 u_int rs_children;
 u_int rs_descendants;
 pid_t rs_reaper;
 pid_t rs_pid;
};
.Ed
The
.Fa rs_flags
may have the following flags returned:
l -tag -width "Dv REAPER_STATUS_REALINIT" t Dv REAPER_STATUS_OWNED The specified process has acquired the reaper status and has not
released it.
When the flag is returned, the specified process
.Fa id ,
pid, identifies the reaper, otherwise the
.Fa rs_reaper
field of the structure is set to the pid of the reaper
for the specified process id.
t Dv REAPER_STATUS_REALINIT The specified process is the root of the reaper tree, i.e.
.Xr init 8 .
.El
The
.Fa rs_children
field returns the number of children of the reaper.
The
.Fa rs_descendants
field returns the total number of descendants of the reaper(s),
not counting descendants of the reaper in the subtree.
The
.Fa rs_reaper
field returns the reaper pid.
The
.Fa rs_pid
returns the pid of one reaper child if there are any descendants.
t Dv PROC_REAP_GETPIDS Queries the list of descendants of the reaper of the specified process.
The request takes a pointer to a
.Vt procctl_reaper_pids
structure in the
.Fa data
parameter.
d -literal struct procctl_reaper_pids {
 u_int rp_count;
 struct procctl_reaper_pidinfo *rp_pids;
};
.Ed
When called, the
.Fa rp_pids
field must point to an array of
.Vt procctl_reaper_pidinfo
structures, to be filled in on return,
and the
.Fa rp_count
field must specify the size of the array,
into which no more than
.Fa rp_count
elements will be filled in by the kernel.
p
The
.Vt "struct procctl_reaper_pidinfo"
structure provides some information about one of the reaper's descendants.
Note that for a descendant that is not a child, it may be incorrectly
identified because of a race in which the original child process exited
and the exited process's pid was reused for an unrelated process.
d -literal struct procctl_reaper_pidinfo {
 pid_t pi_pid;
 pid_t pi_subtree;
 u_int pi_flags;
};
.Ed
The
.Fa pi_pid
field is the process id of the descendant.
The
.Fa pi_subtree
field provides the pid of the child of the reaper, which is the (grand-)parent
of the process.
The
.Fa pi_flags
field returns the following flags, further describing the descendant:
l -tag -width "Dv REAPER_PIDINFO_VALID" t Dv REAPER_PIDINFO_VALID Set to indicate that the
.Vt procctl_reaper_pidinfo
structure was filled in by the kernel.
Zero-filling the
.Fa rp_pids
array and testing the
.Dv REAPER_PIDINFO_VALID
flag allows the caller to detect the end
of the returned array.
t Dv REAPER_PIDINFO_CHILD The
.Fa pi_pid
field identifies the direct child of the reaper.
.El
t Dv PROC_REAP_KILL Request to deliver a signal to some subset of the descendants of the reaper.
The
.Fa data
parameter must point to a
.Vt procctl_reaper_kill
structure, which is used both for parameters and status return.
d -literal struct procctl_reaper_kill {
 int rk_sig;
 u_int rk_flags;
 pid_t rk_subtree;
 u_int rk_killed;
 pid_t rk_fpid;
};
.Ed
The
.Fa rk_sig
field specifies the signal to be delivered.
Zero is not a valid signal number, unlike
.Xr kill 2 .
The
.Fa rk_flags
field further directs the operation.
It is or-ed from the following flags:
l -tag -width "Dv REAPER_KILL_CHILDREN" t Dv REAPER_KILL_CHILDREN Deliver the specified signal only to direct children of the reaper.
t Dv REAPER_KILL_SUBTREE Deliver the specified signal only to descendants that were forked by
the direct child with pid specified in the
.Fa rk_subtree
field.
.El
If neither the
.Dv REAPER_KILL_CHILDREN
nor the
.Dv REAPER_KILL_SUBTREE
flags are specified, all current descendants of the reaper are signalled.
p
If a signal was delivered to any process, the return value from the request
is zero.
In this case, the
.Fa rk_killed
field identifies the number of processes signalled.
The
.Fa rk_fpid
field is set to the pid of the first process for which signal
delivery failed, e.g. due to the permission problems.
If no such process exist, the
.Fa rk_fpid
field is set to -1.
.El
.Sh RETURN VALUES
If an error occurs, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn procctl
system call
will fail if:
l -tag -width Er t Bq Er EFAULT The
.Fa arg
parameter points outside the process's allocated address space.
t Bq Er EINVAL The
.Fa cmd
argument specifies an unsupported command.
p
The
.Fa idtype
argument specifies an unsupported identifier type.
t Bq Er EPERM The calling process does not have permission to perform the requested
operation on any of the selected processes.
t Bq Er ESRCH No processes matched the requested
.Fa idtype
and
.Fa id .
t Bq Er EINVAL An invalid operation or flag was passed in
.Fa arg
for a
.Dv PROC_SPROTECT
command.
t Bq Er EPERM The
.Fa idtype
argument is not equal to
.Dv P_PID ,
or
.Fa id
is not equal to the pid of the calling process, for
.Dv PROC_REAP_ACQUIRE
or
.Dv PROC_REAP_RELEASE
requests.
t Bq Er EINVAL Invalid or undefined flags were passed to a
.Dv PROC_REAP_KILL
request.
t Bq Er EINVAL An invalid or zero signal number was requested for a
.Dv PROC_REAP_KILL
request.
t Bq Er EINVAL The
.Dv PROC_REAP_RELEASE
request was issued by the
.Xr init 8
process.
t Bq Er EBUSY The
.Dv PROC_REAP_ACQUIRE
request was issued by a process that had already acquired reaper status
and has not yet released it.
.El
.Sh SEE ALSO
.Xr kill 2 ,
.Xr ptrace 2 ,
.Xr wait 2 ,
.Xr init 8
.Sh HISTORY
The
.Fn procctl
function appeared in
.Fx 10.0 .
The reaper facility is based on a similar feature of Linux and
DragonflyBSD, and first appeared in
.Fx 10.2 .