NAME¶

UFFDIO_SET_MODE - toggle userfaultfd runtime mode bits

LIBRARY¶

Standard C library (libc, -lc)

SYNOPSIS¶

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

int ioctl(int fd, UFFDIO_SET_MODE, struct uffdio_set_mode *argp);

#include <linux/userfaultfd.h>

struct uffdio_set_mode {
    __u64  enable;   /* Feature bits to set */
    __u64  disable;  /* Feature bits to clear */
};

DESCRIPTION¶

Toggle userfaultfd features that may be flipped at runtime.

Bits set in .enable turn the named features on; bits set in .disable turn them off. The two fields must not overlap. Today only UFFD_FEATURE_RWP_ASYNC is a valid bit in either field; any other bit causes the ioctl to fail with EINVAL. Enabling UFFD_FEATURE_RWP_ASYNC also requires UFFD_FEATURE_RWP to have been negotiated at UFFDIO_API(2const) time.

The operation is serialized against in-flight page faults, so the new mode takes effect only after every fault that started before the call has finished, and any fault that starts after the call observes the new mode. This allows a single userfaultfd to switch between lightweight async detection and synchronous eviction without re-registering its ranges.

RETURN VALUE¶

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

ERRORS¶

EINVAL

A bit other than UFFD_FEATURE_RWP_ASYNC was specified in .enable or .disable.

EINVAL

The fields .enable and .disable overlap.

EINVAL

UFFD_FEATURE_RWP_ASYNC was requested without UFFD_FEATURE_RWP having been negotiated.

EFAULT

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

STANDARDS¶

Linux.

HISTORY¶

Linux 7.2.

EXAMPLES¶

See userfaultfd(2).

SEE ALSO¶

ioctl(2), ioctl_userfaultfd(2), userfaultfd(2)

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