get_robust_list

GET_ROBUST_LIST(2)            Linux System Calls            GET_ROBUST_LIST(2)



NAME
       get_robust_list, set_robust_list - get/set list of robust futexes

SYNOPSIS
       #include <linux/futex.h>
       #include <sys/types.h>
       #include <syscall.h>

       long get_robust_list(int pid, struct robust_list_head **head_ptr,
                            size_t *len_ptr);
       long set_robust_list(struct robust_list_head *head, size_t len);

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

DESCRIPTION
       These system calls deal with per-thread robust futex lists.  These
       lists are managed in user space: the kernel knows only about the
       location of the head of the list.  A thread can inform the kernel of
       the location of its robust futex list using set_robust_list().  The
       address of a thread's robust futex list can be obtained using
       get_robust_list().

       The purpose of the robust futex list is to ensure that if a thread
       accidentally fails to unlock a futex before terminating or calling
       execve(2), another thread that is waiting on that futex is notified
       that the former owner of the futex has died.  This notification
       consists of two pieces: the FUTEX_OWNER_DIED bit is set in the futex
       word, and the kernel performs a futex(2) FUTEX_WAKE operation on one of
       the threads waiting on the futex.

       The get_robust_list() system call returns the head of the robust futex
       list of the thread whose thread ID is specified in pid.  If pid is 0,
       the head of the list for the calling thread is returned.  The list head
       is stored in the location pointed to by head_ptr.  The size of the
       object pointed to by **head_ptr is stored in len_ptr.

       Permission to employ get_robust_list() is governed by a ptrace access
       mode PTRACE_MODE_READ_REALCREDS check; see ptrace(2).

       The set_robust_list() system call requests the kernel to record the
       head of the list of robust futexes owned by the calling thread.  The
       head argument is the list head to record.  The len argument should be
       sizeof(*head).

RETURN VALUE
       The set_robust_list() and get_robust_list() system calls return zero
       when the operation is successful, an error code otherwise.

ERRORS
       The set_robust_list() system call can fail with the following error:

       EINVAL len does not equal sizeof(struct robust_list_head).

       The get_robust_list() system call can fail with the following errors:

       EFAULT The head of the robust futex list can't be stored at the
              location head.

       EPERM  The calling process does not have permission to see the robust
              futex list of the thread with the thread ID pid, and does not
              have the CAP_SYS_PTRACE capability.

       ESRCH  No thread with the thread ID pid could be found.

VERSIONS
       These system calls were added in Linux 2.6.17.

NOTES
       These system calls are not needed by normal applications.  No support
       for them is provided in glibc.  In the unlikely event that you want to
       call them directly, use syscall(2).

       A thread can have only one robust futex list; therefore applications
       that wish to use this functionality should use the robust mutexes
       provided by glibc.

       In the initial implementation, a thread waiting on a futex was notified
       that the owner had died only if the owner terminated.  Starting with
       Linux 2.6.28, notification was extended to include the case where the
       owner performs an execve(2).

       The thread IDs mentioned in the main text are kernel thread IDs of the
       kind returned by clone(2) and gettid(2).

SEE ALSO
       futex(2), pthread_mutexattr_setrobust(3)

       Documentation/robust-futexes.txt and Documentation/robust-futex-ABI.txt
       in the Linux kernel source tree

COLOPHON
       This page is part of release 5.04 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



Linux                             2019-10-10                GET_ROBUST_LIST(2)