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