Ubuntu Manpage: UFFDIO_REGISTER - register a memory address range with the userfaultfd object

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).