sigvec(3) — Linux manual pages

Linux manual pages	Section 3

Name

sigvec, sigblock, sigsetmask, siggetmask, sigmask — BSD signal API

Synopsis

#include <signal.h>

`int sigvec(`	int `sig`,
	struct sigvec *`vec`,
	struct sigvec *`ovec)`;

int sigmask( int signum);

int sigblock( int mask);

int sigsetmask( int mask);

int siggetmask( void);

Note

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
All functions shown above:
`_BSD_SOURCE`

DESCRIPTION

These functions are provided in glibc as a compatibility interface for programs that make use of the historical BSD signal API. This API is obsolete: new applications should use the POSIX signal API (sigaction(2), sigprocmask(2), etc.)

The sigvec() function sets and/or gets the disposition of the signal sig (like the POSIX sigaction(2)). If vec is not NULL, it points to a sigvec structure that defines the new disposition for sig. If ovec is not NULL, it points to a sigvec structure that is used to return the previous disposition of sig. To obtain the current disposition of sig without changing it, specify NULL for vec, and a non-NULL pointer for ovec.

The dispositions for SIGKILL and SIGSTOP cannot be changed.

The sigvec structure has the following form:

struct sigvec {

void (* sv_handler)();
/* Signal disposition */

int sv_mask;
/* Signals to be blocked in handler */

int sv_flags;
/* Flags */

};

The sv_handler field specifies the disposition of the signal, and is either: the address of a signal handler function; or SIG_DFL meaning the default disposition applies for the signal; or SIG_IGN meaning that the signal is ignored.

If sv_handler specifies the address of a signal handler, then sv_mask specifies a mask of signals that are to be blocked while the handler is executing. In addition, the signal for which the handler is invoked is also blocked by default. Attempts to block SIGKILL or SIGSTOP are silently ignored.

If sv_handler specifies the address of a signal handler, then the sv_flags field specifies flags controlling what happens when the handler is called. This field may contain zero or more of the following flags:

SV_INTERRUPT: If the signal handler interrupts a blocking system call, then upon return from the handler the system call will not be restarted: instead it will fail with the error EINTR. If this flag is not specified, then system calls are restarted by default.
SV_RESETHAND: Reset the disposition of the signal to the default before calling the signal handler. If this flag is not specified, then the handler remains established until explicitly removed by a later call to sigvec() or until the process performs an execve(2).
SV_ONSTACK: Handle the signal on the alternate signal stack (historically established under BSD using the obsolete sigstack() function; the POSIX replacement is sigaltstack(2)).

The sigmask() function constructs and returns a "signal mask" for signum. For example, we can initialize the vec.sv_mask field given to sigvec() using code such as the following:

    vec.sv_mask = sigmask(SIGQUIT) | sigpause(SIGABRT);
                /* Block SIGQUIT and SIGABRT during
                   handler execution */

The sigblock() function adds the signals in mask to the process's signal mask (like POSIX sigprocmask(SIG_BLOCK)), and returns the process's previous signal mask. Attempts to block SIGKILL or SIGSTOP are silently ignored.

The sigsetmask() function sets the process's signal mask to the value given in mask (like POSIX sigprocmask(SIG_SETMASK)), and returns the process's previous signal mask.

The siggetmask() function returns the process's current signal mask. This call is equivalent to sigblock(0).

RETURN VALUE

The sigvec() function returns 0 on success; on error, it returns −1 and sets errno to indicate the error.

The sigblock() and sigsetmask() functions return the previous signal mask.

The sigmask() function returns the signal mask for signum.

ERRORS

See the ERRORS under sigaction(2) and sigprocmask(2).

CONFORMING TO

All of these functions were in 4.3BSD, except siggetmask(), whose origin is unclear. These functions are obsolete: do not use them in new programs.

NOTES

On 4.3BSD, the signal() function provided reliable semantics (as when calling sigvec() with vec.sv_mask equal to 0). On System V, signal() provides unreliable semantics. POSIX.1-2001 leaves these aspects of signal() unspecified. See signal(2) for further details.

In order to wait for a signal, BSD and System V both provided a function named sigpause(3), but this function has a different argument on the two systems. See sigpause(3) for details.

COLOPHON

This page is part of release 3.33 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man-pages/.

  t
Copyright (c) 2005 by Michael Kerrisk <mtk.manpagesgmail.com>

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.

struct	sigvec {
	void	(*	`sv_handler`)();	/* Signal disposition */
	int		`sv_mask`;	/* Signals to be blocked in handler */
	int		`sv_flags`;	/* Flags */
};