Ubuntu Manpage: rt_sigqueueinfo, rt_tgsigqueueinfo

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.

VERSIONS

       The  rt_sigqueueinfo() system call was added in Linux 2.2.  The rt_tgsigqueueinfo() system
       call was added in Linux 2.6.31.

STANDARDS

       These system calls are Linux-specific.

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.