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ZERO_REGION(9) FreeBSD Kernel Developer's Manual ZERO_REGION(9)
NAME
zero_region - Read-only region prefilled with zeroes
SYNOPSIS
#include <sys/param.h>
#include <sys/systm.h>
#include <vm/vm_param.h>
extern const void *zero_region;
DESCRIPTION
The global variable zero_region points to a read-only region prefilled
with zeroes. The size of the region is specified by the ZERO_REGION_SIZE
macro.
IMPLEMENTATION NOTES
The region zero_region points to is mapped to the same page multiple
times.
EXAMPLES
/*
* This function writes zeroes to the vnode at offset 0
* with ZERO_REGION_SIZE length.
*/
static int
write_example(struct vnode *vp)
{
struct thread *td;
struct iovec aiov;
struct uio auio;
int error;
td = curthread;
aiov.iov_base = __DECONST(void *, zero_region);
aiov.iov_len = ZERO_REGION_SIZE;
auio.uio_iov = &aiov;
auio.uio_iovcnt = 1;
auio.uio_offset = 0;
auio.uio_resid = ZERO_REGION_SIZE;
auio.uio_segflg = UIO_SYSSPACE;
auio.uio_rw = UIO_WRITE;
auio.uio_td = td;
error = VOP_WRITE(vp, &auio, 0, td->td_ucred);
return (error);
}
SEE ALSO
pmap(9), vm_map(9)
AUTHORS
This manual page was written by Ka Ho Ng <khng@FreeBSDFoundation.org>
under sponsorship from the FreeBSD Foundation.
FreeBSD 14.0-RELEASE-p6 March 2, 2021 FreeBSD 14.0-RELEASE-p6