NAME

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

SYNOPSIS

     #include <sys/types.h>
     #include <sys/systm.h>

     int
     casueword(volatile u_long *base, u_long oldval, u_long *oldvalp, u_long newval);

     int
     casueword32(volatile uint32_t *base, uint32_t oldval, uint32_t *oldvalp, uint32_t newval);

     u_long
     casuword(volatile u_long *base, u_long oldval, u_long newval);

     uint32_t
     casuword32(volatile uint32_t *base, uint32_t oldval, uint32_t newval);

DESCRIPTION

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

     The casueword 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 casueword32() and
     casueword(), old value is stored into the (kernel-mode) variable pointed by *oldvalp.  The userspace value
     must be naturally aligned.

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

RETURN VALUES

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

SEE ALSO

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