NAME

UFFDIO_REGISTER - register a memory address range with the userfaultfd object

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#include <linux/userfaultfd.h>  /* Definition of UFFD* constants */
#include <sys/ioctl.h>

int ioctl(int fd, UFFDIO_REGISTER, struct uffdio_register *argp);

#include <linux/userfaultfd.h>

struct uffdio_range {
    __u64  start;   /* Start of range */
    __u64  len;     /* Length of range (bytes) */
};
struct uffdio_register {
    struct uffdio_range  range;
    __u64                mode;    /* Desired mode of operation (input) */
    __u64                ioctls;  /* Available ioctl()s (output) */
};

DESCRIPTION

Register a memory address range with the userfaultfd object. The pages in the range must be “compatible”. Please refer to the list of register modes below for the compatible memory backends for each mode.

The argp->range field defines a memory range starting at argp->range.start and continuing for argp->range.len bytes that should be handled by the userfaultfd.

The argp->mode field defines the mode of operation desired for this memory region. The following values may be bitwise ORed to set the userfaultfd mode for the specified range:

UFFDIO_REGISTER_MODE_MISSING

Track page faults on missing pages. Since Linux 4.3, only private anonymous ranges are compatible. Since Linux 4.11, hugetlbfs and shared memory ranges are also compatible.

UFFDIO_REGISTER_MODE_WP

Track page faults on write-protected pages. Since Linux 5.7, only private anonymous ranges are compatible.

UFFDIO_REGISTER_MODE_MINOR

Track minor page faults. Since Linux 5.13, only hugetlbfs ranges are compatible. Since Linux 5.14, compatibility with shmem ranges was added.

If the operation is successful, the kernel modifies the argp->ioctls bit-mask field to indicate which ioctl(2) operations are available for the specified range. This returned bit mask can contain the following bits:

1 << _UFFDIO_COPY

The UFFDIO_COPY operation is supported.

1 << _UFFDIO_WAKE

The UFFDIO_WAKE operation is supported.

1 << _UFFDIO_WRITEPROTECT

The UFFDIO_WRITEPROTECT operation is supported.

1 << _UFFDIO_ZEROPAGE

The UFFDIO_ZEROPAGE operation is supported.

1 << _UFFDIO_CONTINUE

The UFFDIO_CONTINUE operation is supported.

1 << _UFFDIO_POISON

The UFFDIO_POISON operation is supported.

RETURN VALUE

On success, 0 is returned. On error, -1 is returned and errno is set to indicate the error.

ERRORS

EBUSY

A mapping in the specified range is registered with another userfaultfd object.

EFAULT

argp refers to an address that is outside the calling process's accessible address space.

EINVAL

An invalid or unsupported bit was specified in the mode field; or the mode field was zero.

EINVAL

There is no mapping in the specified address range.

EINVAL

range.start or range.len is not a multiple of the system page size; or, range.len is zero; or these fields are otherwise invalid.

EINVAL

There as an incompatible mapping in the specified address range.

STANDARDS

Linux.

HISTORY

Linux 4.3.

EXAMPLES

See userfaultfd(2).

SEE ALSO

ioctl(2), ioctl_userfaultfd(2), UFFDIO_UNREGISTER(2const), userfaultfd(2)

linux.git/Documentation/admin-guide/mm/userfaultfd.rst