1/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
2#ifndef _LINUX_FUTEX_H
3#define _LINUX_FUTEX_H
4
5
6#include <linux/types.h>
7
8/* Second argument to futex syscall */
9
10
11#define FUTEX_WAIT 0
12#define FUTEX_WAKE 1
13#define FUTEX_FD 2
14#define FUTEX_REQUEUE 3
15#define FUTEX_CMP_REQUEUE 4
16#define FUTEX_WAKE_OP 5
17#define FUTEX_LOCK_PI 6
18#define FUTEX_UNLOCK_PI 7
19#define FUTEX_TRYLOCK_PI 8
20#define FUTEX_WAIT_BITSET 9
21#define FUTEX_WAKE_BITSET 10
22#define FUTEX_WAIT_REQUEUE_PI 11
23#define FUTEX_CMP_REQUEUE_PI 12
24#define FUTEX_LOCK_PI2 13
25
26#define FUTEX_PRIVATE_FLAG 128
27#define FUTEX_CLOCK_REALTIME 256
28#define FUTEX_CMD_MASK ~(FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
29
30#define FUTEX_WAIT_PRIVATE (FUTEX_WAIT | FUTEX_PRIVATE_FLAG)
31#define FUTEX_WAKE_PRIVATE (FUTEX_WAKE | FUTEX_PRIVATE_FLAG)
32#define FUTEX_REQUEUE_PRIVATE (FUTEX_REQUEUE | FUTEX_PRIVATE_FLAG)
33#define FUTEX_CMP_REQUEUE_PRIVATE (FUTEX_CMP_REQUEUE | FUTEX_PRIVATE_FLAG)
34#define FUTEX_WAKE_OP_PRIVATE (FUTEX_WAKE_OP | FUTEX_PRIVATE_FLAG)
35#define FUTEX_LOCK_PI_PRIVATE (FUTEX_LOCK_PI | FUTEX_PRIVATE_FLAG)
36#define FUTEX_LOCK_PI2_PRIVATE (FUTEX_LOCK_PI2 | FUTEX_PRIVATE_FLAG)
37#define FUTEX_UNLOCK_PI_PRIVATE (FUTEX_UNLOCK_PI | FUTEX_PRIVATE_FLAG)
38#define FUTEX_TRYLOCK_PI_PRIVATE (FUTEX_TRYLOCK_PI | FUTEX_PRIVATE_FLAG)
39#define FUTEX_WAIT_BITSET_PRIVATE (FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG)
40#define FUTEX_WAKE_BITSET_PRIVATE (FUTEX_WAKE_BITSET | FUTEX_PRIVATE_FLAG)
41#define FUTEX_WAIT_REQUEUE_PI_PRIVATE (FUTEX_WAIT_REQUEUE_PI | \
42 FUTEX_PRIVATE_FLAG)
43#define FUTEX_CMP_REQUEUE_PI_PRIVATE (FUTEX_CMP_REQUEUE_PI | \
44 FUTEX_PRIVATE_FLAG)
45
46/*
47 * Support for robust futexes: the kernel cleans up held futexes at
48 * thread exit time.
49 */
50
51/*
52 * Per-lock list entry - embedded in user-space locks, somewhere close
53 * to the futex field. (Note: user-space uses a double-linked list to
54 * achieve O(1) list add and remove, but the kernel only needs to know
55 * about the forward link)
56 *
57 * NOTE: this structure is part of the syscall ABI, and must not be
58 * changed.
59 */
60struct robust_list {
61 struct robust_list *next;
62};
63
64/*
65 * Per-thread list head:
66 *
67 * NOTE: this structure is part of the syscall ABI, and must only be
68 * changed if the change is first communicated with the glibc folks.
69 * (When an incompatible change is done, we'll increase the structure
70 * size, which glibc will detect)
71 */
72struct robust_list_head {
73 /*
74 * The head of the list. Points back to itself if empty:
75 */
76 struct robust_list list;
77
78 /*
79 * This relative offset is set by user-space, it gives the kernel
80 * the relative position of the futex field to examine. This way
81 * we keep userspace flexible, to freely shape its data-structure,
82 * without hardcoding any particular offset into the kernel:
83 */
84 long futex_offset;
85
86 /*
87 * The death of the thread may race with userspace setting
88 * up a lock's links. So to handle this race, userspace first
89 * sets this field to the address of the to-be-taken lock,
90 * then does the lock acquire, and then adds itself to the
91 * list, and then clears this field. Hence the kernel will
92 * always have full knowledge of all locks that the thread
93 * _might_ have taken. We check the owner TID in any case,
94 * so only truly owned locks will be handled.
95 */
96 struct robust_list *list_op_pending;
97};
98
99/*
100 * Are there any waiters for this robust futex:
101 */
102#define FUTEX_WAITERS 0x80000000
103
104/*
105 * The kernel signals via this bit that a thread holding a futex
106 * has exited without unlocking the futex. The kernel also does
107 * a FUTEX_WAKE on such futexes, after setting the bit, to wake
108 * up any possible waiters:
109 */
110#define FUTEX_OWNER_DIED 0x40000000
111
112/*
113 * The rest of the robust-futex field is for the TID:
114 */
115#define FUTEX_TID_MASK 0x3fffffff
116
117/*
118 * This limit protects against a deliberately circular list.
119 * (Not worth introducing an rlimit for it)
120 */
121#define ROBUST_LIST_LIMIT 2048
122
123/*
124 * bitset with all bits set for the FUTEX_xxx_BITSET OPs to request a
125 * match of any bit.
126 */
127#define FUTEX_BITSET_MATCH_ANY 0xffffffff
128
129
130#define FUTEX_OP_SET 0 /* *(int *)UADDR2 = OPARG; */
131#define FUTEX_OP_ADD 1 /* *(int *)UADDR2 += OPARG; */
132#define FUTEX_OP_OR 2 /* *(int *)UADDR2 |= OPARG; */
133#define FUTEX_OP_ANDN 3 /* *(int *)UADDR2 &= ~OPARG; */
134#define FUTEX_OP_XOR 4 /* *(int *)UADDR2 ^= OPARG; */
135
136#define FUTEX_OP_OPARG_SHIFT 8 /* Use (1 << OPARG) instead of OPARG. */
137
138#define FUTEX_OP_CMP_EQ 0 /* if (oldval == CMPARG) wake */
139#define FUTEX_OP_CMP_NE 1 /* if (oldval != CMPARG) wake */
140#define FUTEX_OP_CMP_LT 2 /* if (oldval < CMPARG) wake */
141#define FUTEX_OP_CMP_LE 3 /* if (oldval <= CMPARG) wake */
142#define FUTEX_OP_CMP_GT 4 /* if (oldval > CMPARG) wake */
143#define FUTEX_OP_CMP_GE 5 /* if (oldval >= CMPARG) wake */
144
145/* FUTEX_WAKE_OP will perform atomically
146 int oldval = *(int *)UADDR2;
147 *(int *)UADDR2 = oldval OP OPARG;
148 if (oldval CMP CMPARG)
149 wake UADDR2; */
150
151#define FUTEX_OP(op, oparg, cmp, cmparg) \
152 (((op & 0xf) << 28) | ((cmp & 0xf) << 24) \
153 | ((oparg & 0xfff) << 12) | (cmparg & 0xfff))
154
155#endif /* _LINUX_FUTEX_H */
156

source code of include/linux/futex.h