Manual Pages  — ZERO_REGION

zero_region – Read-only region prefilled with zeroes

SYNOPSIS DESCRIPTION IMPLEMENTATION NOTES EXAMPLES SEE ALSO AUTHORS

#include <sys/param.h>

#include <sys/systm.h>

#include <vm/vm_param.h>

extern const void *zero_region;

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.

The region zero_region points to is mapped to the same page multiple times.

/*
 * 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);
}

This manual page was written by Ka Ho Ng <Mt khng@FreeBSDFoundation.org> under sponsorship from the FreeBSD Foundation.