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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)