Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
CASU(9)			 BSD Kernel Developer's	Manual		       CASU(9)

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 suc-
     cess and -1 on failure.

SEE ALSO
     atomic(9),	fetch(9), store(9)

BSD			       October 21, 2014				   BSD

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | SEE ALSO

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=casueword&sektion=9&manpath=FreeBSD+12.0-RELEASE+and+Ports>

home | help