casueword (9)

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Part of this documentation was written by
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from the FreeBSD Foundation.

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(The comments found at the beginning of the groff file "man9/casueword.9freebsd".)

NAME

casueword casueword32 casuword casuword32 - fetch, compare and store data from user-space

SYNOPSIS

In sys/types.h In sys/systm.h Ft int Fn casueword volatile u_long *base u_long oldval u_long *oldvalp u_long newval Ft int Fn casueword32 volatile uint32_t *base uint32_t oldval uint32_t *oldvalp uint32_t newval Ft u_long Fn casuword volatile u_long *base u_long oldval u_long newval Ft uint32_t Fn casuword32 volatile uint32_t *base uint32_t oldval uint32_t newval

DESCRIPTION

The functions are designed to perform atomic compare-and-swap operation on the value in the usermode memory of the current process.

The routines reads the value from user memory with address base and compare the value read with oldval If the values are equal, newval is written to the *base In case of Fn casueword32 and Fn casueword , old value is stored into the (kernel-mode) variable pointed by *oldvalp The userspace value must be naturally aligned.

The callers of Fn casuword and Fn casuword32 functions cannot distinguish between -1 read from userspace and function failure.

RETURN VALUES

The Fn casuword and Fn casuword32 functions return the data fetched or -1 on failure. The Fn casueword and Fn casueword32 functions return 0 on success and -1 on failure.

SEE ALSO

atomic(9), fetch(9), store(9)