NAME
sigvec —
software signal
facilities
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <signal.h>
struct sigvec {
void (*sv_handler)();
int sv_mask;
int sv_flags;
};
int
sigvec(
int
sig,
struct sigvec
*vec,
struct sigvec
*ovec);
DESCRIPTION
This interface is
made obsolete by
sigaction(2). The structure,
flags, and function declaration have been removed from the header files but
the function is kept in the c library for binary compatibility.
The system defines a set of signals that may be delivered to a process. Signal
delivery resembles the occurrence of a hardware interrupt: the signal is
blocked from further occurrence, the current process context is saved, and a
new one is built. A process may specify a
handler to which a
signal is delivered, or specify that a signal is to be
ignored. A process may also specify that a default action is
to be taken by the system when a signal occurs. A signal may also be
blocked, in which case its delivery is postponed until it is
unblocked. The action to be taken on delivery is determined
at the time of delivery. Normally, signal handlers execute on the current
stack of the process. This may be changed, on a per-handler basis, so that
signals are taken on a special
signal stack.
Signal routines execute with the signal that caused their invocation
blocked, but other signals may yet occur. A global
signal mask defines the set of signals currently blocked
from delivery to a process. The signal mask for a process is initialized from
that of its parent (normally 0). It may be changed with a
sigblock(3) or
sigsetmask(3) call, or when
a signal is delivered to the process.
When a signal condition arises for a process, the signal is added to a set of
signals pending for the process. If the signal is not currently
blocked by the process then it is delivered to the process.
When a caught signal is delivered, the current state of the process is saved,
a new signal mask is calculated (as described below), and the signal handler
is invoked. The call to the handler is arranged so that if the signal handling
routine returns normally the process will resume execution in the context from
before the signal's delivery. If the process wishes to resume in a different
context, then it must arrange to restore the previous context itself.
When a signal is delivered to a process a new signal mask is installed for the
duration of the process' signal handler (or until a
sigblock(3) or
sigsetmask(3) call is made).
This mask is formed by taking the union of the current signal mask, the signal
to be delivered, and the signal mask associated with the handler to be
invoked.
sigvec() assigns a handler for a specific signal. If
vec is non-zero, it specifies an action
(
SIG_DFL
,
SIG_IGN
, or a
handler routine) and mask to be used when delivering the specified signal.
Further, if the
SV_ONSTACK
bit is set in
sv_flags, the system will deliver the signal to the
process on a
signal stack, specified with
sigaltstack(2). If
ovec is non-zero, the previous handling information for
the signal is returned to the user.
Once a signal handler is installed, it remains installed until another
sigvec() call is made, or an
execve(2) is performed. A
signal-specific default action may be reset by setting
sv_handler to
SIG_DFL
. The
defaults are process termination, possibly with core dump; no action; stopping
the process; or continuing the process. See the signal list below for each
signal's default action. If
sv_handler is set to
SIG_DFL
, the default action for the signal is to
discard the signal, and if a signal is pending, the pending signal is
discarded even if the signal is masked. If
sv_handler is
set to
SIG_IGN
, current and pending instances of the
signal are ignored and discarded.
Options may be specified by setting
sv_flags. If the
SV_ONSTACK
bit is set in
sv_flags, the system will deliver the signal to the
process on a
signal stack, specified with
sigstack(2).
If a signal is caught during the system calls listed below, the call may be
restarted, the call may return with a data transfer shorter than requested, or
the call may be forced to terminate with the error
EINTR
. Interrupting of pending calls is requested by
setting the
SV_INTERRUPT
bit in
sv_flags. The affected system calls include
open(2),
read(2),
write(2),
sendto(2),
recvfrom(2),
sendmsg(2) and
recvmsg(2) on a communications
channel or a slow device (such as a terminal, but not a regular file) and
during a
wait(2) or
ioctl(2). However, calls that
have already committed are not restarted, but instead return a partial success
(for example, a short read count).
After a
fork(2) or
vfork(2) all signals, the signal
mask, the signal stack, and the interrupt/restart flags are inherited by the
child.
The
execve(2) system call
reinstates the default action for all signals which were caught and resets all
signals to be caught on the user stack. Ignored signals remain ignored; the
signal mask remains the same; signals that interrupt pending system calls
continue to do so.
See
signal(7) for comprehensive
list of supported signals.
NOTES
The mask specified in
vec is not allowed to block
SIGKILL
or
SIGSTOP
. This is
enforced silently by the system.
The
SV_INTERRUPT
flag is not available in
4.2BSD, hence it should not be used if backward
compatibility is needed.
RETURN VALUES
A 0 value indicated that the call succeeded. A -1 return value indicates an
error occurred and
errno is set to indicated the reason.
EXAMPLES
The handler routine can be declared:
void
handler(sig, code, scp)
int sig, code;
struct sigcontext *scp;
Here
sig is the signal number, into which the hardware
faults and traps are mapped as defined below.
code is a
parameter that is either a constant or the code provided by the hardware.
scp is a pointer to the
sigcontext
structure (defined in
<signal.h>),
used to restore the context from before the signal.
ERRORS
sigvec() will fail and no new signal handler will be installed
if one of the following occurs:
-
-
- [
EFAULT
]
- Either vec or
ovec points to memory that is not a valid part of
the process address space.
-
-
- [
EINVAL
]
- sig is not a valid signal
number.
-
-
- [
EINVAL
]
- An attempt is made to ignore or supply a handler for
SIGKILL
or SIGSTOP
.
SEE ALSO
kill(1),
kill(2),
ptrace(2),
sigaction(2),
sigaltstack(2),
sigprocmask(2),
sigstack(2),
sigsuspend(2),
setjmp(3),
sigblock(3),
siginterrupt(3),
signal(3),
sigpause(3),
sigsetmask(3),
sigsetops(3),
tty(4),
signal(7)