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RT_SIGQUEUEINFO(2) Linux Programmer's Manual RT_SIGQUEUEINFO(2)
NAME
rt_sigqueueinfo, rt_tgsigqueueinfo - queue a signal and data
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 cor‐
responds 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 cur‐
rently 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 de‐
fined 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 to Linux in version 2.2. The rt_tgsigqueueinfo() system call was added to Linux in version 2.6.31.
CONFORMING TO
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.
SEE ALSO
kill(2), pidfd_send_signal(2), sigaction(2), sigprocmask(2), tgkill(2), pthread_sigqueue(3), sigqueue(3), signal(7)
Linux 2021-03-22 RT_SIGQUEUEINFO(2)