CASUWORD32(9FREEBSD) - Linux man page online | System kernel interfaces

Fetch, compare and store data from user-space.

October 21, 2014
CASU(9) BSD Kernel Developer's Manual CASU(9)


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


#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);


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.


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.


atomic(9), fetch(9), store(9)
BSD October 21, 2014 BSD
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refer to atomic(9freebsd) | fetch(9freebsd) | store(9freebsd)
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