NetBSD/lib/libc/compat-43/sigvec.3

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.\"     from: @(#)sigvec.2	8.2 (Berkeley) 4/19/94
.\"
.Dd November 1, 1997
.Dt SIGVEC 3
.Os
.Sh NAME
.Nm sigvec
.Nd software signal facilities
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include <signal.h>
.Bd -literal
struct sigvec {
	void	(*sv_handler)();
	int	sv_mask;
	int	sv_flags;
};
.Ed
.Ft int
.Fn sigvec "int sig" "struct sigvec *vec" "struct sigvec *ovec"
.Sh DESCRIPTION
.Bf -symbolic
This interface is made obsolete by
.Xr sigaction 2 .
.Ef
.Pp
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
.Em handler
to which a signal is delivered, or specify that a signal is to be
.Em 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
.Em blocked ,
in which case its delivery is postponed until it is
.Em 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
.Em "signal stack" .
.Pp
Signal routines execute with the signal that caused their
invocation
.Em blocked ,
but other signals may yet occur.
A global
.Em "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
.Xr sigblock 3
or
.Xr sigsetmask 3
call, or when a signal is delivered to the process.
.Pp
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
.Em 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.
.Pp
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
.Xr sigblock 3
or
.Xr 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.
.Pp
.Fn sigvec
assigns a handler for a specific signal.
If
.Fa vec
is non-zero, it
specifies an action
.Pf ( Dv SIG_DFL ,
.Dv SIG_IGN ,
or a handler routine) and mask
to be used when delivering the specified signal.
Further, if the
.Dv SV_ONSTACK
bit is set in
.Fa sv_flags ,
the system will deliver the signal to the process on a
.Em "signal stack" ,
specified with
.Xr sigaltstack 2 .
If
.Fa ovec
is non-zero, the previous handling information for the signal
is returned to the user.
.Pp
Once a signal handler is installed, it remains installed
until another
.Fn sigvec
call is made, or an
.Xr execve 2
is performed.
A signal-specific default action may be reset by
setting
.Fa sv_handler
to
.Dv 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
.Fa sv_handler
is set to
.Dv 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
.Fa sv_handler
is set to
.Dv SIG_IGN ,
current and pending instances
of the signal are ignored and discarded.
.Pp
Options may be specified by setting
.Em sv_flags .
If the
.Dv SV_ONSTACK
bit is set in
.Fa sv_flags ,
the system will deliver the signal to the process on a
.Em "signal stack" ,
specified with
.Xr sigstack 2 .
.Pp
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 forced to terminate
with the error
.Dv EINTR .
Interrupting of pending calls is requested
by setting the
.Dv SV_INTERRUPT
bit in
.Ar sv_flags .
The affected system calls include
.Xr open 2 ,
.Xr read 2 ,
.Xr write 2 ,
.Xr sendto 2 ,
.Xr recvfrom 2 ,
.Xr sendmsg 2
and
.Xr recvmsg 2
on a communications channel or a slow device (such as a terminal,
but not a regular file)
and during a
.Xr wait 2
or
.Xr ioctl 2 .
However, calls that have already committed are not restarted,
but instead return a partial success (for example, a short read count).
.Pp
After a
.Xr fork 2
or
.Xr vfork 2
all signals, the signal mask, the signal stack,
and the interrupt/restart flags are inherited by the child.
.Pp
The
.Xr 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.
.Pp
See
.Xr signal 7
for comprehensive list of supported signals.
.Sh NOTES
The mask specified in
.Fa vec
is not allowed to block
.Dv SIGKILL
or
.Dv SIGSTOP .
This is enforced silently by the system.
.Pp
The
.Dv SV_INTERRUPT
flag is not available in
.Bx 4.2 ,
hence it should not be used if backward compatibility is needed.
.Sh RETURN VALUES
A 0 value indicated that the call succeeded.
A \-1 return value indicates an error occurred and
.Va errno
is set to indicated the reason.
.Sh EXAMPLE
The handler routine can be declared:
.Bd -literal -offset indent
void
handler(sig, code, scp)
	int sig, code;
	struct sigcontext *scp;
.Ed
.Pp
Here
.Fa sig
is the signal number, into which the hardware faults and traps are
mapped as defined below.
.Fa code
is a parameter that is either a constant
or the code provided by the hardware.
.Fa scp
is a pointer to the
.Fa sigcontext
structure (defined in
.Aq Pa signal.h ) ,
used to restore the context from before the signal.
.Sh ERRORS
.Fn sigvec
will fail and no new signal handler will be installed if one
of the following occurs:
.Bl -tag -width Er
.It Bq Er EFAULT
Either
.Fa vec
or
.Fa ovec
points to memory that is not a valid part of the process
address space.
.It Bq Er EINVAL
.Fa sig
is not a valid signal number.
.It Bq Er EINVAL
An attempt is made to ignore or supply a handler for
.Dv SIGKILL
or
.Dv SIGSTOP .
.El
.Sh SEE ALSO
.Xr kill 1 ,
.Xr kill 2 ,
.Xr ptrace 2 ,
.Xr sigaction 2 ,
.Xr sigaltstack 2 ,
.Xr sigprocmask 2 ,
.Xr sigstack 2 ,
.Xr sigsuspend 2 ,
.Xr setjmp 3 ,
.Xr sigblock 3 ,
.Xr siginterrupt 3 ,
.Xr signal 3 ,
.Xr sigpause 3 ,
.Xr sigsetmask 3 ,
.Xr sigsetops 3 ,
.Xr tty 4 ,
.Xr signal 7