NULLOP(9) BSD Kernel Developer's Manual NULLOP(9)NAME
nullop -- dummy functions
SYNOPSIS
#include <sys/systm.h>
int
nullop(void *v);
void
voidop(void);
int
enodev(void);
int
enxio(void);
int
enoioctl(void);
int
enosys(void);
int
eopnotsupp(void);
DESCRIPTION
The nullop() function provides a generic ``null operation''. It always returns the value 0. The voidop() function takes no arguments and
does nothing.
The enodev(), enxio(), enoioctl(), enosys(), and eopnotsupp() functions always fail, returning ENODEV, ENXIO, ENOTTY, ENOSYS, and EOPNOTSUPP,
respectively.
EXAMPLES
The following example demonstrates a case where nullop() may be useful:
uint64_t xc;
...
xc = xc_broadcast(0, (xcfunc_t)nullop, NULL, NULL);
xc_wait(xc);
BSD July 25, 2010 BSD
Check Out this Related Man Page
UCAS(9) BSD Kernel Developer's Manual UCAS(9)NAME
ucas -- atomic memory operations on user-space address
SYNOPSIS
#include <sys/systm.h>
int
ucas_ptr(volatile void *uptr, void *old, void *new, void *retp);
int
ucas_int(volatile int *uptr, int old, int new, int *retp);
DESCRIPTION
These functions provide compare-and-swap (CAS) functionality on user-space address.
Except that they can be safely used for the kernel to access user-space address, they are semantically equivalents of atomic_cas(3).
uptr The pointer to the variable. This should be a user-space pointer.
old The value to compare with the variable.
new The value to store to the variable.
retp The pointer to the memory to store the old value of the variable.
RETURN VALUES
On success, these functions return 0. In that case, the caller can consult the value returned via retp to check the result of the CAS opera-
tion. Otherwise, these functions return an appropriate errno(9) error code, typically EFAULT.
SEE ALSO atomic_cas(3), intro(9)BUGS
Conceptually, the retp argument of ucas_ptr() would be of void **. The current prototype is a compromise for usability.
BSD October 24, 2011 BSD
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