linux-kernel - Re: userfaultfd: two-step UFFDIO

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Message-ID: <2dd0bcee-a594-4de9-b499-a8ad37be155c@yandex.ru>
Date: Tue, 26 Nov 2024 10:32:28 +0300
From: stsp <stsp2@...dex.ru>
To: Muhammad Usama Anjum <Usama.Anjum@...labora.com>,
 Peter Xu <peterx@...hat.com>
Cc: Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: userfaultfd: two-step UFFDIO_API always gives -EINVAL

25.11.2024 21:44, Muhammad Usama Anjum пишет:
> The UFFD_FEATURE_WP_ASYNC was designed for exactly this case.
> The IOCTL will return you the modified pages. An example of usage
> can be found in selftest/mm/pagemap_ioctl.c.
Thank you!
I studied the examples.
They are quite clear and good
for copy/pasting purposes.

I had yet another "problem":
I tried to create the usefaultfd,
then register the API and fork()
the process. In child I do UFFDIO_REGISTER,
but the parent can't see that.
So instead of copy by fork, I
had to use SCM_RIGHTS.
Is this expected, or should it
work fine with forked fd? That
would be a bit simpler than to
apply to SCM_RIGHTS tricks.