Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

eopnotsupp(9) [netbsd man page]

NULLOP(9)						   BSD Kernel Developer's Manual						 NULLOP(9)

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

XCALL(9)						   BSD Kernel Developer's Manual						  XCALL(9)

xcall, xc_broadcast, xc_unicast, xc_wait -- cross-call interface SYNOPSIS
#include <sys/xcall.h> typedef void (*xcfunc_t)(void *, void *); uint64_t xc_broadcast(u_int flags, xcfunc_t func, void *arg1, void *arg2); uint64_t xc_unicast(u_int flags, xcfunc_t func, void *arg1, void *arg2, struct cpu_info *ci); void xc_wait(uint64_t where); DESCRIPTION
The machine-independent xcall interface allows any CPU in the system to request that an arbitrary function be executed on any other CPU. Sometimes it is necessary to modify hardware state that is tied directly to individual CPUs (such as a CPU's local timer), and these updates can not be done remotely by another CPU. The LWP requesting the update may be unable to guarantee that it will be running on the CPU where the update must occur, when the update occurs. Additionally, it is sometimes necessary to modify per-CPU software state from a remote CPU. Where these update operations are so rare or the access to the per-CPU data so frequent that the cost of using locking or atomic operations to provide coherency is prohibitive, another way must be found. Cross calls help to solve these types of problem. However, since this facility is heavyweight, it is expected that it will not be used often. xcall provides a mechanism for making ``low priority'' cross calls. The function to be executed runs on the remote CPU within a thread con- text, and not from a software interrupt, so it can ensure that it is not interrupting other code running on the CPU, and so has exclusive access to the CPU. Keep in mind that unless disabled, it may cause a kernel preemption. xcall also provides a mechanism for making ``high priority'' cross calls. The function to be executed runs on the remote CPU within a IPL_SOFTCLOCK software interrupt context, possibly interrupting other lower-priority code running on the CPU. NOTES
Functions being called should be relatively lightweight. They may block on locks, but carefully and minimally, to not interfere with other cross calls in the system. FUNCTIONS
xc_broadcast(flags, func, arg1, arg2) Call (*func)(arg1, arg2) on all CPUs in the system. Return a uint64_t ``ticket'' to xc_wait() on for the cross-call to complete. flags should be XC_HIGHPRI for a "high priority" call, and 0 for a "low priority" call. xc_broadcast() should not be called from interrupt context. xc_unicast(flags, func, arg1, arg2, ci) Like xc_broadcast(), but call (*func)() on only the CPU indicated by ci. xc_unicast() also returns a ``ticket''. xc_wait(where) Wait on the ``ticket'' returned by a prior xc_broadcast() or xc_unicast() for the corresponding cross-call to complete. xc_wait() should be called from a thread context. CODE REFERENCES
The xcall interface is implemented within the file sys/kern/subr_xcall.c. SEE ALSO
kpreempt(9), percpu(9) HISTORY
The xcall interface first appeared in NetBSD 5.0. AUTHORS
Andrew Doran <> BSD
October 24, 2011 BSD
Man Page