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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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UFFDIO_SET_MODE(2const) UFFDIO_SET_MODE(2const)
UFFDIO_SET_MODE - toggle userfaultfd runtime mode bits
Standard C library (libc, -lc)
#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 */
};
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.
On success, 0 is returned. On error, -1 is returned and errno is
set to indicate the error.
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.
Linux.
Linux 7.2.
See userfaultfd(2).
ioctl(2), ioctl_userfaultfd(2), userfaultfd(2)
linux.git/Documentation/admin-guide/mm/userfaultfd.rst
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
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2026-09-09. If you discover any rendering problems in this HTML
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Linux man-pages 6.19 2026-05-28 UFFDIO_SET_MODE(2const)
Pages that refer to this page: ioctl_userfaultfd(2), UFFDIO_API(2const)
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HTML rendering created 2026-09-09 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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