rt_sigqueueinfo(2)

NAME
rt_sigqueueinfo, rt_tgsigqueueinfo - queue a signal and data

LIBRARY
Standard C library (libc, -lc)

SYNOPSIS
#include <linux/signal.h>     /* Definition of SI_* constants */
#include <sys/syscall.h>      /* Definition of SYS_* constants */
#include <unistd.h>

int syscall(SYS_rt_sigqueueinfo, pid_t tgid,
            int sig, siginfo_t *info);
int syscall(SYS_rt_tgsigqueueinfo, pid_t tgid, pid_t tid,
            int sig, siginfo_t *info);

Note: There are no glibc wrappers for these system calls; see NOTES.

DESCRIPTION
The rt_sigqueueinfo() and rt_tgsigqueueinfo() system calls are the low-level interfaces used to send a signal plus data to a process or thread. The receiver of the signal can obtain the accompanying data by establishing a signal handler with the sigaction(2) SA_SIGINFO flag.

These system calls are not intended for direct application use; they are provided to allow the implementation of sigqueue(3) and pthread_sigqueue(3).

The rt_sigqueueinfo() system call sends the signal sig to the thread group with the ID tgid. (The term "thread group" is synonymous with "process", and tid corresponds to the traditional UNIX process ID.) The signal will be delivered to an arbitrary member of the thread group (i.e., one of the threads that is not currently blocking the signal).

The info argument specifies the data to accompany the signal. This argument is a pointer to a structure of type siginfo_t, described in sigaction(2) (and defined by including <sigaction.h>). The caller should set the following fields in this structure:

si_code
    This should be one of the SI_* codes in the Linux kernel source file include/asm-generic/siginfo.h. If the signal is being sent to any process other than the caller itself, the following restrictions apply:

    •   The code can't be a value greater than or equal to zero. In particular, it can't be SI_USER, which is used by the kernel to indicate a signal sent by kill(2), and nor can it be SI_KERNEL, which is used to indicate a signal generated by the kernel.

    •   The code can't (since Linux 2.6.39) be SI_TKILL, which is used by the kernel to indicate a signal sent using tgkill(2).

si_pid
    This should be set to a process ID, typically the process ID of the sender.

si_uid
    This should be set to a user ID, typically the real user ID of the sender.

si_value
    This field contains the user data to accompany the signal. For more information, see the description of the last (union sigval) argument of sigqueue(3).

Internally, the kernel sets the si_signo field to the value specified in sig, so that the receiver of the signal can also obtain the signal number via that field.

The rt_tgsigqueueinfo() system call is like rt_sigqueueinfo(), but sends the signal and data to the single thread specified by the combination of tgid, a thread group ID, and tid, a thread in that thread group.

RETURN VALUE
On success, these system calls return 0. On error, they return -1 and errno is set to indicate the error.

ERRORS

EAGAIN
    The limit of signals which may be queued has been reached. (See signal(7) for further information.)

EINVAL
    sig, tgid, or tid was invalid.

EPERM
    The caller does not have permission to send the signal to the target. For the required permissions, see kill(2).

EPERM
    tgid specifies a process other than the caller and info->si_code is invalid.

ESRCH
    rt_sigqueueinfo(): No thread group matching tgid was found.

rt_tgsigqueinfo(): No thread matching tgid and tid was found.

STANDARDS
Linux.

HISTORY

rt_sigqueueinfo()
    Linux 2.2.

rt_tgsigqueueinfo()
    Linux 2.6.31.

NOTES
Since these system calls are not intended for application use, there are no glibc wrapper functions; use syscall(2) in the unlikely case that you want to call them directly.

As with kill(2), the null signal (0) can be used to check if the specified process or thread exists.

SEE ALSO
kill(2), pidfd_send_signal(2), sigaction(2), sigprocmask(2), tgkill(2), pthread_sigqueue(3), sigqueue(3), signal(7)