man2/get_robust_list.2

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  26 .\" FIXME Something could be added to this page (or exit(2))
  27 .\"       about exit_robust_list processing
  28 .\"
  29 .TH GET_ROBUST_LIST 2 2016-07-17 Linux "Linux System Calls"
  30 .SH NAME
  31 get_robust_list, set_robust_list \- get/set list of robust futexes
  32 .SH SYNOPSIS
  33 .nf
  34 .B #include <linux/futex.h>
  35 .B #include <sys/types.h>
  36 .B #include <syscall.h>
  37 .sp
  38 .BI "long get_robust_list(int " pid ", struct robust_list_head **" head_ptr ,
  39 .BI "                     size_t *" len_ptr );
  40 .BI "long set_robust_list(struct robust_list_head *" head ", size_t " len );
  41 .fi
  42
  43 .IR Note :
  44 There are no glibc wrappers for these system calls; see NOTES.
  45 .SH DESCRIPTION
  46 The robust futex implementation needs to maintain per-thread lists of
  47 the robust futexes which are to be unlocked when the thread exits.
  48 These lists are managed in user space; the kernel is notified about only
  49 the location of the head of the list.
  50
  51 The
  52 .BR get_robust_list ()
  53 system call returns the head of the robust futex list of the thread
  54 whose thread ID is specified in
  55 .IR pid .
  56 If
  57 .I pid
  58 is 0,
  59 the head of the list for the calling thread is returned.
  60 The list head is stored in the location pointed to by
  61 .IR head_ptr .
  62 The size of the object pointed to by
  63 .I **head_ptr
  64 is stored in
  65 .IR len_ptr .
  66
  67 Permission to employ
  68 .BR get_robust_list ()
  69 is governed by a ptrace access mode
  70 .B PTRACE_MODE_READ_REALCREDS
  71 check; see
  72 .BR ptrace (2).
  73
  74 The
  75 .BR set_robust_list ()
  76 system call requests the kernel to record the head of the list of
  77 robust futexes owned by the calling thread.
  78 The
  79 .I head
  80 argument is the list head to record.
  81 The
  82 .I len
  83 argument should be
  84 .IR sizeof(*head) .
  85 .SH RETURN VALUE
  86 The
  87 .BR set_robust_list ()
  88 and
  89 .BR get_robust_list ()
  90 system calls return zero when the operation is successful,
  91 an error code otherwise.
  92 .SH ERRORS
  93 The
  94 .BR set_robust_list ()
  95 system call can fail with the following error:
  96 .TP
  97 .B EINVAL
  98 .I len
  99 does not equal
 100 .IR "sizeof(struct\ robust_list_head)" .
 101 .PP
 102 The
 103 .BR get_robust_list ()
 104 system call can fail with the following errors:
 105 .TP
 106 .B EPERM
 107 The calling process does not have permission to see the robust futex list of
 108 the thread with the thread ID
 109 .IR pid ,
 110 and does not have the
 111 .BR CAP_SYS_PTRACE
 112 capability.
 113 .TP
 114 .B ESRCH
 115 No thread with the thread ID
 116 .I pid
 117 could be found.
 118 .TP
 119 .B EFAULT
 120 The head of the robust futex list can't be stored at the location
 121 .IR head .
 122 .SH VERSIONS
 123 These system calls were added in Linux 2.6.17.
 124 .SH NOTES
 125 These system calls are not needed by normal applications.
 126 No support for them is provided in glibc.
 127 In the unlikely event that you want to call them directly, use
 128 .BR syscall (2).
 129
 130 A thread can have only one robust futex list;
 131 therefore applications that wish
 132 to use this functionality should use the robust mutexes provided by glibc.
 133 .SH SEE ALSO
 134 .BR futex (2)
 135 .\" .BR pthread_mutexattr_setrobust_np (3)
 136
 137 .IR Documentation/robust-futexes.txt
 138 and
 139 .IR Documentation/robust-futex-ABI.txt
 140 in the Linux kernel source tree
 141 .\" http://lwn.net/Articles/172149/