ntsync(4)

The driver implements the ntsync interface as specified in the Linux
7.0-rc3 document Documentation/userspace-api/ntsync.rst. Only the
documentation and the userspace tests (Linux'
tools/

ntsync(4)

The driver implements the ntsync interface as specified in the Linux
7.0-rc3 document Documentation/userspace-api/ntsync.rst. Only the
documentation and the userspace tests (Linux'
tools/testing/selftests/drivers/ntsync/ntsync.c) were used for
reference. When the documentation contradicted the tests, tests
behavior was implemented.

One quirk is that Linux API needs to return an error from ioctl() and to
copyout the modified ioctl() argument. Our generic ioctl() is not flexible
enough to implement this, so the ntsync_ioctl_copyout() hack allows to
copyout the ioctl parameter directly from the ioctl method, instead of
relying on the ioctl infra.

The FreeBSD port of the tests, that can be compiled both on FreeBSD and
Linux, is available at https://github.com/kostikbel/freebsd-ntsync-test.
The Linux binary compiled with the Linux test harness, cannot be run
under linuxolator due to unimplemented syscalls, but the shims in
freebsd-ntsync-test can be compiled on Linux and resulting Linux/glibc
binary run on linuxolator to test linux compat.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D57038

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