Overhaul documentation of the kernel signal facilities. Some text
liberally borrowed from Paul's psignal(9) manpage. More work can be done here, but there's more here than before, at least.
This commit is contained in:
thorpej
parent
384ed56864
commit
3acbaeb040
@ -1,4 +1,4 @@
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# $NetBSD: Makefile,v 1.112 2002/06/24 22:45:41 gmcgarry Exp $
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# $NetBSD: Makefile,v 1.113 2002/07/09 02:28:10 thorpej Exp $
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# Makefile for section 9 (kernel function and variable) manual pages.
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@ -21,9 +21,9 @@ MAN= access.9 altq.9 arc4random.9 arp.9 audio.9 autoconf.9 \
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panic.9 pci.9 pci_configure_bus.9 pci_intr.9 \
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pcmcia.9 pfil.9 physio.9 \
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pmap.9 pool.9 powerhook_establish.9 ppsratecheck.9 properties.9 \
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psignal.9 radio.9 rasops.9 ratecheck.9 resettodr.9 rnd.9 rt_timer.9 \
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radio.9 rasops.9 ratecheck.9 resettodr.9 rnd.9 rt_timer.9 \
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scsipi.9 setjmp.9 setrunqueue.9 shutdownhook_establish.9 \
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sleep.9 softintr.9 \
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signal.9 sleep.9 softintr.9 \
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spl.9 store.9 suser.9 tc.9 time.9 todr.9 uiomove.9 ucom.9 \
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vattr.9 vfs.9 vfsops.9 vme.9 vnode.9 vnodeops.9 vnsubr.9 \
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usbdi.9 uvm.9 wdc.9 wscons.9 wsdisplay.9 wsfont.9 wskbd.9 wsmouse.9
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@ -266,7 +266,6 @@ MLINKS+=properties.9 propdb_create.9 \
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properties.9 prop_list.9 \
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properties.9 prop_objs.9 \
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properties.9 prop_set.9
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MLINKS+=psignal.9 pgsignal.9 psignal.9 gsignal.9
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MLINKS+=rasops.9 rasops_init.9 \
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rasops.9 rasops_reconfig.9
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MLINKS+=rnd.9 rnd_attach_source.9 rnd.9 rnd_detach_source.9 \
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@ -277,6 +276,29 @@ MLINKS+=rt_timer.9 rt_timer_queue_create.9 rt_timer.9 rt_timer_queue_change.9 \
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MLINKS+=setjmp.9 longjmp.9
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MLINKS+=setrunqueue.9 remrunqueue.9
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MLINKS+=shutdownhook_establish.9 shutdownhook_disestablish.9
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MLINKS+=signal.9 siginit.9 \
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signal.9 sigactsinit.9 \
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signal.9 sigactsunshare.9 \
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signal.9 sigactsfree.9 \
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signal.9 execsigs.9 \
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signal.9 sigaction1.9 \
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signal.9 sigprocmask1.9 \
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signal.9 sigpending1.9 \
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signal.9 sigsuspend1.9 \
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signal.9 sigaltstack1.9 \
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signal.9 gsignal.9 \
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signal.9 pgsignal.9 \
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signal.9 trapsignal.9 \
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signal.9 psignal.9 \
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signal.9 sched_psignal.9 \
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signal.9 issignal.9 \
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signal.9 postsig.9 \
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signal.9 killproc.9 \
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signal.9 sigexit.9 \
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signal.9 sigmasked.9 \
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signal.9 sendsig.9 \
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signal.9 sigcode.9 \
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signal.9 sigtramp.9
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MLINKS+=sleep.9 wakeup.9 sleep.9 tsleep.9 sleep.9 ltsleep.9
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MLINKS+=softintr.9 softintr_establish.9 softintr.9 softintr_disestablish.9 \
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softintr.9 softintr_schedule.9
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@ -1,143 +0,0 @@
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.\" $NetBSD: psignal.9,v 1.5 1999/03/16 00:40:47 garbled Exp $
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.\"
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.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Paul Kranenburg.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
|
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.\" are met:
|
||||
.\" 1. Redistributions of source code must retain the above copyright
|
||||
.\" notice, this list of conditions and the following disclaimer.
|
||||
.\" 2. Redistributions in binary form must reproduce the above copyright
|
||||
.\" notice, this list of conditions and the following disclaimer in the
|
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
|
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.\" contributors may be used to endorse or promote products derived
|
||||
.\" from this software without specific prior written permission.
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.\"
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||||
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
||||
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
|
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
||||
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
|
||||
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
||||
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
||||
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
||||
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd June 22, 1996
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.Dt PSIGNAL 9
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.Os
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.Sh NAME
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.Nm psignal ,
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.Nm pgsignal ,
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.Nm gsignal
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.Nd post signal to a process
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.Sh SYNOPSIS
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.Ft void
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.Fn "psignal" "struct proc *p" "int signum"
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.Ft void
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.Fn "pgsignal" "struct pgrp *pgrp" "int signum" "int checkctty"
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.Ft void
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.Fn "gsignal" "int pgid" "int signum"
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.Sh DESCRIPTION
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These functions post a signal to one or more processes.
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The argument
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.Fa signum
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common to all three functions should be in the range
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.Bq 1- Ns Dv NSIG .
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.Pp
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The
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.Fn psignal
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function posts signal number
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.Fa signum
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to the process represented by the process structure
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.Fa p .
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With a few exceptions noted below, the target process signal disposition is
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updated and is marked as runnable, so further handling of the signal is done
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in the context of the target process after a context switch.
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Note that
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.Fn psignal
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does not by itself cause a context switch to happen.
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.Pp
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The target process is not marked as runnable in the following cases:
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.Bl -bullet -offset indent
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.It
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The target process is sleeping uninterruptibly.
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The signal will be
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noticed when the process returns from the system call or trap.
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.It
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The target process is currently ignoring the signal.
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.It
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If a stop signal is sent to a sleeping process that takes the
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default action
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.Pq see Xr sigaction 2 ,
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the process is stopped without awakening it.
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.It
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.Dv SIGCONT
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restarts a stopped process
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.Pq or puts them back to sleep
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regardless of the signal action
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.Pq e.g., blocked or ignored .
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.El
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.Pp
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If the target process is being traced
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.Fn psignal
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behaves as if the target process were taking the default action for
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.Fa signum .
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This allows the tracing process to be notified of the signal.
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.Pp
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The
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.Fn pgsignal
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function posts signal number
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.Fa signum
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to each member of the process group described by
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.Fa pgrp .
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If
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.Fa checkctty
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is non-zero, the signal will be posted only to processes that have
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a controlling terminal.
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.Fn pgsignal
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is implemented by walking along the process list headed by the field
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.Li pg_members
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of the process group structure
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pointed at by
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.Fa pgrp
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and calling
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.Fn psignal
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as appropriate.
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If
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.Fa pgrp
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is
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.Dv NULL
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no action is taken.
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.Pp
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The
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.Fn gsignal
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function posts signal number
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.Fa signum
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to each member of the process group identified by the group id
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.Fa pgid .
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.Fn gsignal
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first finds the group structure associated with
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.Fa pgid ,
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then invokes
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.Fn pgsignal
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with the argument
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.Fa checkctty
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set to zero.
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If
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.Fa pgid
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is zero no action is taken.
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.Sh SEE ALSO
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.Xr sigaction 2 ,
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.Xr tsleep 9
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501
share/man/man9/signal.9
Normal file
501
share/man/man9/signal.9
Normal file
@ -0,0 +1,501 @@
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.\" $NetBSD: signal.9,v 1.1 2002/07/09 02:28:08 thorpej Exp $
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.\"
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.\" Copyright (c) 1996, 2002 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Paul Kranenburg and Jason R. Thorpe.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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||||
.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
|
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
|
||||
.\" contributors may be used to endorse or promote products derived
|
||||
.\" from this software without specific prior written permission.
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.\"
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||||
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
||||
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
|
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
||||
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
|
||||
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
||||
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
||||
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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||||
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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||||
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
||||
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd July 8, 2002
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.Dt SIGNAL 9
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.Os
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.Sh NAME
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.Nm signal ,
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.Nm siginit ,
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.Nm sigactsinit ,
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.Nm sigactsunshare ,
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.Nm sigactsfree ,
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.Nm execsigs ,
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.Nm sigaction1 ,
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.Nm sigprocmask1 ,
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.Nm sigpending1 ,
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.Nm sigsuspend1 ,
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.Nm sigaltstack1 ,
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.Nm gsignal ,
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.Nm pgsignal ,
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.Nm trapsignal ,
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.Nm psignal ,
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.Nm sched_psignal ,
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.Nm issignal ,
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.Nm postsig ,
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.Nm killproc ,
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.Nm sigexit ,
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.Nm sigmasked ,
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.Nm sendsig ,
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.Nm sigcode ,
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.Nm sigtramp ,
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.Nd software signal facilities
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.Sh SYNOPSIS
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.Fd #include \*[Lt]sys/signal.h\*[Gt]
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.Fd #include \*[Lt]sys/signalvar.h\*[Gt]
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.Ft void
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.Fn siginit "struct proc *p"
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.Ft void
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.Fn sigactsinit "struct proc *np" "struct proc *pp" "int share"
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.Ft void
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.Fn sigactsunsuare "struct proc *p"
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.Ft void
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.Fn sigactsfree "struct proc *p"
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.Ft void
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.Fn execsigs "struct proc *p"
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.Ft int
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.Fn sigaction1 "struct proc *p" "int signum" "const struct sigaction *nsa" \
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"struct sigaction *osa" "void *tramp" "int vers"
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.Ft int
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.Fn sigprocmask1 "struct proc *p" "int how" "const sigset_t *nss" \
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"sigset_t *oss"
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.Ft void
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.Fn sigpending1 "struct proc *p" "sigset_t *ss"
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.Ft int
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.Fn sigsuspend1 "struct proc *p" "const sigset_t *ss"
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.Ft int
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.Fn sigaltstack1 "struct proc *p" "const struct sigaltstack *nss" \
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"struct sigaltstack *oss"
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.Ft void
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.Fn gsignal "int pgid" "int signum"
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.Ft void
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.Fn pgsignal "struct pgrp *pgrp" "int signum" "int checkctty"
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.Ft void
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.Fn trapsignal "struct proc *p" "int signum" "u_long code"
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.Ft void
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.Fn psignal "struct proc *p" "int signum"
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.Ft void
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.Fn sched_psignal "struct proc *p" "int signum"
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.Ft int
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.Fn issignal "struct proc *p"
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.Ft void
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.Fn postsig "int signum"
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.Ft void
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.Fn killproc "struct proc *p" "char *why"
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.Ft void
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.Fn sigexit "struct proc *p" "int signum"
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.Ft int
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.Fn sigmasked "struct proc *p" "int signum"
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.Ft void
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.Fn sendsig "int signum" "sigset_t *mask" "u_long code"
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.Sh DESCRIPTION
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The system defines a set of signals that may be delivered to a process.
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These functions implement the kernel portion of the signal facility.
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.Pp
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Signal numbers used throughout the kernel signal facilities should
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always be within the range of
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.Bq 1- Ns NSIG .
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.Pp
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Most of the kernel's signal infrastructure is implemented in
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machine-independent code. Machine-dependent code provides
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support for invoking a process's signal handler, restoring
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context when the signal handler returns, generating signals
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when hardware traps occur, triggering the delivery of signals
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when a process is about to return from the kernel to userspace.
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.Pp
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The signal state for a process is contained in
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.Fa struct sigctx .
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This includes the list of signals with delivery pending,
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information about the signal handler stack, the signal mask, and the
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address of the signal trampoline.
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.Pp
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The registered signal handlers for a process are recorded in
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.Fa struct sigacts .
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This structure may be shared by multiple processes.
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.Pp
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The kernel's signal facilities are implemented by the following
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functions:
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.Bl -tag -width XXXXX
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.It void Fn siginit "struct proc *p"
|
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.Pp
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This function initializes the signal state of
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.Va proc0
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to the system default. This signal state is then inherited by
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.Xr init 8
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when it is started by the kernel.
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.It void Fn sigactsinit "struct proc *np" "struct proc *pp" "int share"
|
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.Pp
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||||
This function creates an initial
|
||||
.Fa struct sigacts
|
||||
for the process
|
||||
.Fa np .
|
||||
If the
|
||||
.Fa share
|
||||
argument is non-zero, then
|
||||
.Fa np
|
||||
shares the
|
||||
.Fa struct sigacts
|
||||
with the process
|
||||
.Fa pp .
|
||||
Otherwise,
|
||||
.Fa np
|
||||
receives a new
|
||||
.Fa struct sigacts
|
||||
which is copied from
|
||||
.Fa pp
|
||||
if non-NULL.
|
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.It void Fn sigactsunshare "struct proc *p"
|
||||
.Pp
|
||||
This function causes the process
|
||||
.Fa p
|
||||
to no longer share its
|
||||
.Fa struct sigacts
|
||||
The current state of the signal actions is maintained in the new copy.
|
||||
.It void Fn sigactsfree "struct proc *p"
|
||||
.Pp
|
||||
This function decrements the reference count on the
|
||||
.Fa struct sigacts
|
||||
of process
|
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.Fa p .
|
||||
If the reference count reaches zero, the
|
||||
.Fa struct sigacts
|
||||
is freed.
|
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.It void Fn execsigs "struct proc *p"
|
||||
.Pp
|
||||
This function is used to reset the signal state of the process
|
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.Fa p
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||||
to the system defaults when the process execs a new program image.
|
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.It int Fn sigaction1 "struct proc *p" "int signum" \
|
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"const struct sigaction *nsa" "struct sigaction *osa" \
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"void *tramp" "int vers"
|
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.Pp
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This function implements the
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.Xr sigaction 2
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system call. The
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.Fa tramp
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and
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.Fa vers
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arguments provide support for userspace signal trampolines.
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Trampoline version 0 is reserved for the legacy kernel-provided
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signal trampoline;
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.Fa tramp
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must be NULL in this case. Otherwise,
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.Fa vers
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specifies the ABI of the trampoline specified by
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.Fa tramp .
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The signal trampoline ABI is machine-dependent, and must be cooridinated
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with the
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.Fn sendsig
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function.
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.It int Fn sigprocmask1 "struct proc *p" "int how" "const sigset_t *nss" \
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"sigset_t *oss"
|
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.Pp
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This function implements the
|
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.Xr sigprocmask 2
|
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system call.
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.It void Fn sigpending1 "struct proc *p" "sigset_t *ss"
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.Pp
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This function implements the
|
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.Xr sigpending 2
|
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system call.
|
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.It int Fn sigsuspend1 "struct proc *p" "const sigset_t *ss"
|
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.Pp
|
||||
This function implements the
|
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.Xr sigsuspend 2
|
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system call.
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.It int Fn sigaltstack1 "struct proc *p" "const struct sigaltstack *nss" \
|
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"struct sigaltstack *oss"
|
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.Pp
|
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This function implements the
|
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.Xr sigaltstack 2
|
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system call.
|
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.It void Fn gsignal "int pgid" "int signum"
|
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.Pp
|
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Schedule the signal
|
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.Fa signum
|
||||
to be delivered to all members of the process group specified by
|
||||
.Fa pgid .
|
||||
See
|
||||
.Fn psignal
|
||||
below for a complete description of the signal scheduling semantics.
|
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.It void Fn pgsignal "struct pgrp *pgrp" "int signum" "int checkctty"
|
||||
.Pp
|
||||
Schedule the signal
|
||||
.Fa signum
|
||||
to be delivered to all members of the process group
|
||||
.Fa pgrp .
|
||||
If
|
||||
.Fa checkctty
|
||||
is non-zero, the signal is only sent to processes which have a
|
||||
controlling terminal. See
|
||||
.Fn psignal
|
||||
below for a complete description of the signal scheduling semantics.
|
||||
.It void Fn trapsignal "struct proc *p" "int signum" "u_long code"
|
||||
.Pp
|
||||
Sends the signal
|
||||
.Fa signum
|
||||
with code
|
||||
.Fa code
|
||||
caused by a hardware trap to the process
|
||||
.Fa p .
|
||||
This function is meant to be called by machine-dependent trap handling
|
||||
code.
|
||||
.It void Fn psignal "struct proc *p" "int signum"
|
||||
.Pp
|
||||
Schedule the signal
|
||||
.Fa signum
|
||||
to be delivered to the process
|
||||
.Fa p .
|
||||
With a few exceptions noted below, the target process signal disposition is
|
||||
updated and is marked as runnable, so further handling of the signal is done
|
||||
in the context of the target process after a context switch; see
|
||||
.Fn issignal
|
||||
below.
|
||||
Note that
|
||||
.Fn psignal
|
||||
does not by itself cause a context switch to happen.
|
||||
.Pp
|
||||
The target process is not marked as runnable in the following cases:
|
||||
.Bl -bullet -offset indent
|
||||
.It
|
||||
The target process is sleeping uninterruptibly. The signal will be
|
||||
noticed when the process returns from the system call or trap.
|
||||
.It
|
||||
The target process is currently ignoring the signal.
|
||||
.It
|
||||
If a stop signal is sent to a sleeping process that takes the
|
||||
default action
|
||||
.Pq see Xr sigaction 2 ,
|
||||
the process is stopped without awakening it.
|
||||
.It
|
||||
SIGCONT
|
||||
restarts a stopped process
|
||||
.Pq or puts them back to sleep
|
||||
regardless of the signal action
|
||||
.Pq e.g., blocked or ignored .
|
||||
.El
|
||||
.Pp
|
||||
If the target process is being traced,
|
||||
.Fn psignal
|
||||
behaves as if the target process were taking the default action for
|
||||
.Fa signum .
|
||||
This allows the tracing process to be notified of the signal.
|
||||
.It void Fn sched_psignal "struct proc *p" "int signum"
|
||||
.Pp
|
||||
An alternate version of
|
||||
.Fn psignal
|
||||
which is intended for use by code which holds the scheduler lock.
|
||||
.It int Fn issignal "struct proc *p"
|
||||
.Pp
|
||||
This function determines which signal, if any, is to be posted to
|
||||
the process
|
||||
.Fa p .
|
||||
A signal is to be posted if:
|
||||
.Bl -bullet -offset indent
|
||||
.It
|
||||
The signal has a handler provided by the program image.
|
||||
.It
|
||||
The signal should cause the process to dump core and/or terminate.
|
||||
.It
|
||||
The signal should interrupt the current system call.
|
||||
.El
|
||||
.Pp
|
||||
Signals which cause the process to be stopped are handled within
|
||||
.Fn issignal
|
||||
directly.
|
||||
.Pp
|
||||
.Fn issignal
|
||||
should be called by machine-dependent code when returning to
|
||||
userspace from a system call or other trap or interrupt by
|
||||
using the following code:
|
||||
.Bd -literal -offset indent
|
||||
while (signum = CURSIG(curproc))
|
||||
postsig(signum);
|
||||
.Ed
|
||||
.Pp
|
||||
.It void Fn postsig "int signum"
|
||||
.Pp
|
||||
The
|
||||
.Fn postsig
|
||||
function is used to invoke the action for the signal
|
||||
.Fa signum
|
||||
in the current process. If the default action of a signal
|
||||
is to terminate the process, and the signal does not have
|
||||
a registered handler, the process exits using
|
||||
.Fn sigexit ,
|
||||
dumping a core image if necessary.
|
||||
.It void Fn killproc "struct proc *p" "char *why"
|
||||
.Pp
|
||||
This function sends a SIGKILL signal to the specified process. The
|
||||
message provided by
|
||||
.Fa why
|
||||
is sent to the system log and is also displayed on the process's
|
||||
controlling terminal.
|
||||
.It void Fn sigexit "struct proc *p" "int signum"
|
||||
.Pp
|
||||
This function forces the process
|
||||
.Fa p
|
||||
to exit with the signal
|
||||
.Fa signum ,
|
||||
generating a core file if appropriate. No checks are made for masked
|
||||
or caught signals; the process always exits.
|
||||
.It int Fn sigmasked "struct proc *p" "int signum"
|
||||
.Pp
|
||||
This function returns non-zero if the signal specifed by
|
||||
.Fa signum
|
||||
is ignored or masked for process
|
||||
.Fa p .
|
||||
.It void Fn sendsig "int sig" "sigset_t *mask" "u_long code"
|
||||
.Pp
|
||||
This function is provided by machine-dependent code, and is used to
|
||||
invoke a signal handler for the current process.
|
||||
.Fn sendsig
|
||||
must prepare the registers and stack of the current process to
|
||||
invoke the signal handler stored in the process's
|
||||
.Fa struct sigacts .
|
||||
This may include switching to an alternate signal
|
||||
stack specified by the process. The previous register, stack,
|
||||
and signal state are stored in a
|
||||
.Fa struct sigcontext ,
|
||||
which is then copied out to the user's stack.
|
||||
.Pp
|
||||
The registers and stack must be set up to invoke the singal handler as
|
||||
follows:
|
||||
.Bd -literal -offset indent
|
||||
(*handler)(signum, code, scp)
|
||||
.Ed
|
||||
.Pp
|
||||
where
|
||||
.Fa signum
|
||||
is the signal number,
|
||||
.Fa code
|
||||
is a signal-specific code, and
|
||||
.Fa scp
|
||||
is the pointer to the
|
||||
.Fa struct sigcontext
|
||||
on the user's stack. The registers and stack must also
|
||||
arrange for the signal handler to return to the signal trampoline.
|
||||
The trampoline is then used to return to the code which was executing
|
||||
when the signal was delivered using the
|
||||
.Xr sigreturn 2
|
||||
system call.
|
||||
.Pp
|
||||
For performance reasons, it is recommended that
|
||||
.Fn sendsig
|
||||
arrange for the signal handler to be invoked directly on architectures
|
||||
where it is convenient to do so. In this case, the trampoline is used
|
||||
only for the signal return path. If it is not feasible to directly
|
||||
invoke the signal handler, the trampoline is also used to invoke the
|
||||
handler, performing any final set up that was not possible for
|
||||
.Fn sendsig
|
||||
to perform.
|
||||
.Pp
|
||||
.Fn sendsig
|
||||
must invoke the signal trampoline with the correct ABI. The ABI of
|
||||
the signal trampoline is specified on a per-signal basis in the
|
||||
.Fn sigacts
|
||||
structure for the process. Trampoline version 0 is reserved for the
|
||||
legacy kernel-provided, on-stack signal trampoline. All other trampoline
|
||||
versions indicate a specific trampoline ABI. This ABI is coordinated
|
||||
with machine-dependent code in the system C library.
|
||||
.El
|
||||
.Ss SIGNAL TRAMPOLINE
|
||||
The signal trampoline is a special piece of code which provides
|
||||
support for invoking the signal handlers for a process. The trampoline
|
||||
is used to return from the signal handler back to the code which was
|
||||
executing when the signal was delivered, and is also used to invoke the
|
||||
handler itself on architectures where it is not feasible to have the
|
||||
kernel invoke the handler directly.
|
||||
.Pp
|
||||
In traditional
|
||||
.Ux
|
||||
systems, the signal trampoline, also referred to as the
|
||||
.Dq sigcode ,
|
||||
is provided by the kernel and copied to the top of the user's
|
||||
stack when a new process is created or a new program image is
|
||||
exec'd. Starting in
|
||||
.Nx 2.0 ,
|
||||
the signal trampoline is provided by the system C library. This
|
||||
allows for more flexibility when the signal facility is extended,
|
||||
makes dealing with signals easier in debuggers, such as
|
||||
.Xr gdb 1 ,
|
||||
and may also enhance system security by allowing the kernel to
|
||||
disallow execution of code on the stack.
|
||||
.Pp
|
||||
The signal trampoline is specified on a per-signal basis. The
|
||||
correct trampoline is selected automatically by the C library
|
||||
when a signal handler is registered by a process.
|
||||
.Pp
|
||||
Signal trampolines have a special naming convention which enables
|
||||
debuggers to determine the characteristics of the signal handler
|
||||
and its arguments. Trampoline functions are named like so:
|
||||
.Bd -literal -offset indent
|
||||
__sigtramp_\*[Lt]flavor\*[Gt]_\*[Lt]version\*[Gt]
|
||||
.Ed
|
||||
.Pp
|
||||
where:
|
||||
.Bl -tag -width versionXX
|
||||
.It \*[Lt]flavor\*[Gt]
|
||||
The flavor of the signal handler. The following flavors are valid:
|
||||
.Bl -tag -width sigcontextXX
|
||||
.It sigcontext
|
||||
Specifies a traditional BSD-style signal handler with the following
|
||||
signature:
|
||||
.Bd -literal
|
||||
void (*handler)(int signum,
|
||||
int code,
|
||||
struct sigcontext *scp);
|
||||
.Ed
|
||||
.It siginfo
|
||||
Specifies a POSIX-style signal handler with the following signature:
|
||||
.Bd -literal
|
||||
void (*handler)(int signum,
|
||||
struct siginfo *si,
|
||||
void *uc);
|
||||
.Ed
|
||||
.Pp
|
||||
Note: support for POSIX-style signal
|
||||
handlers is not yet implemented in the
|
||||
.Nx
|
||||
kernel.
|
||||
.El
|
||||
.It \*[Lt]version\*[Gt]
|
||||
Specifies the ABI version of the signal trampoline. The trampoline
|
||||
ABI is coordinated with the machine-dependent kernel
|
||||
.Fn sendsig
|
||||
function.
|
||||
.El
|
||||
.Pp
|
||||
The following is an example if a signal trampoline name which indicates
|
||||
that the trampoline is used for traditional BSD-style signal handlers
|
||||
and implements version 1 of the signal trampoline ABI:
|
||||
.Bd -literal -offset indent
|
||||
__sigtramp_sigcontext_1
|
||||
.Ed
|
||||
.Sh SEE ALSO
|
||||
.Xr sigaction 2 ,
|
||||
.Xr signal 7 ,
|
||||
.Xr tsleep 9
|
||||
Loading…
x
Reference in New Issue
Block a user