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39 .Nd fetch, compare and store data from user-space
45 .Fa "volatile u_long *base"
52 .Fa "volatile uint32_t *base"
54 .Fa "uint32_t *oldvalp"
59 .Fa "volatile u_long *base"
65 .Fa "volatile uint32_t *base"
72 functions are designed to perform atomic compare-and-swap operation on
73 the value in the usermode memory of the current process.
77 routines reads the value from user memory with address
79 and compare the value read with
81 If the values are equal,
89 old value is stored into the (kernel-mode) variable pointed by
91 The userspace value must be naturally aligned.
97 functions cannot distinguish between -1 read from
98 userspace and function failure.
104 functions return the data fetched or -1 on failure.
109 functions return 0 on success, -1 on failure to access memory,
110 and 1 when comparison or store failed.
111 The store can fail on load-linked/store-conditional architectures.