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1 .\" $NetBSD: _lwp_ctl.2,v 1.5 2012/04/13 15:14:58 yamt Exp $
2 .\"
3 .\" Copyright (c)2007 YAMAMOTO Takashi,
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27 .\" ------------------------------------------------------------
28 .Dd April 13, 2012
29 .Dt _LWP_CTL 2
30 .Os
31 .Sh NAME
32 .Nm _lwp_ctl
33 .Nd prepare per-LWP communication area between kernel and userland
34 .\" ------------------------------------------------------------
35 .Sh LIBRARY
36 .Lb libc
37 .\" ------------------------------------------------------------
38 .Sh SYNOPSIS
39 .In sys/lwpctl.h
40 .In lwp.h
41 .Ft int
42 .Fn _lwp_ctl "int features" "struct lwpctl **address"
43 .\" ------------------------------------------------------------
44 .Sh DESCRIPTION
45 .Fn _lwp_ctl
46 prepares per-LWP communication area for the calling LWP,
47 and maps it into the calling process' address space.
48 It takes the following arguments.
49 .Bl -tag -width features
50 .It Fa features
51 The bitwise-OR of the following flags.
52 .Bl -tag -width LWPCTL_FEATURE_CURCPU
53 .It Dv LWPCTL_FEATURE_CURCPU
54 Request
55 .Vt lc_curcpu .
56 .It Dv LWPCTL_FEATURE_PCTR
57 Request
58 .Vt lc_pctr .
59 .El
60 .It Fa address
61 The address to store a pointer to
62 .Vt lwpctl
63 structure for the calling LWP.
64 .El
65 .Pp
66 The per-LWP communication area is described by an
67 .Vt lwpctl
68 structure.
69 It has following members, depending on
70 .Fa features .
71 .Bl -tag -width int_lc_curcpu
72 .It Vt int lc_curcpu
73 The integral identifier of the CPU on which the LWP is running,
74 or
75 .Dv LWPCTL_CPU_NONE
76 when the LWP is not running on any CPU.
77 It's updated by the kernel and should be considered as read-only for
78 userland.
79 It's available only if requested with the
80 .Dv LWPCTL_FEATURE_CURCPU
81 flag.
82 .It Vt int lc_pctr
83 The integer which is incremented on every context switches to the LWP.
84 It can be used to detect preemption of the LWP.
85 (thus its name "preemption counter".)
86 It's updated by the kernel and should be considered as read-only for
87 userland.
88 It's available only if requested with the
89 .Dv LWPCTL_FEATURE_PCTR
90 flag.
91 .El
92 .\" ------------------------------------------------------------
93 .Sh RETURN VALUES
94 .Fn _lwp_ctl
95 returns 0 on success.
96 Otherwise, \-1 is returned and
97 .Va errno
98 is set to indicate the error.
99 .\" ------------------------------------------------------------
100 .\".Sh ERRORS
101 .\" ------------------------------------------------------------
102 .Sh SEE ALSO
103 .Xr errno 2