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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dmXc/1pXGW2+/HEeumfywZ51IU4Hs5ACQTZujqaS/qyTSxTlsOeh8HFq8IulI9qqu 1uX2Fb+M5C9jdIceHxJ1lmQxiJY1GZm8asgiujFw5MmKrRdh/QqKflnkizvac1oZAB 57w1VbzOAW4CAdDxdRUSaAZ1MUUHO5yPdcSK6Pn0pNnC+iWKqOsC7AOJ0o67I2FRR7 sdLEBHKlWv1K4WaxL5E4yVIntF7vVbXJMupEw8UY/QrIXCEeSO57MNDIjKjWtiWMh9 i66AoBMSH7j1uMEHB8iVA7n5QrRXc1LJyz/LJhnIATMmUI/mgPf4X9RUbC+8AQotBg SRix/cACrcuKw== Date: Tue, 26 Sep 2023 01:32:15 +0200 From: Alejandro Colomar To: Axel Rasmussen Cc: Peter Xu , linux-man@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 03/10] userfaultfd.2: comment on feature detection in the example program Message-ID: References: <20230919190206.388896-1-axelrasmussen@google.com> <20230919190206.388896-4-axelrasmussen@google.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="7eflzcifipfkwrsh" Content-Disposition: inline In-Reply-To: <20230919190206.388896-4-axelrasmussen@google.com> X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: B9A9940005 X-Stat-Signature: 8h8a18913jhyxqk579dm7m819y6pxr7f X-Rspam-User: X-HE-Tag: 1695684740-205420 X-HE-Meta: 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 Tlo0UJhb HoFIQ1+xk5hD1R7MXpTMVqpePjo7pNQuOpuEllx5uduSIj4RgGpDulWe81pgZhD/vs4CPhf57ufSglWbkMy8ztRmwsPFPUtdysiP2xuFTBeDa29VDlOqsabkbwh3xAeHmyTN19prScskjnWRmMosotnokq/uljCnSmECIPy4h/Jw6zYfKpCwXuFqYaW4fAwBv8Rz6kQ6dtKl3GPgcEjx02H/DJPb3HvdoDk62LAcg9SI+Opx6X0d0Fz+7w0Mo0kOdvObIXoIgkmS34R6ns7b7tO3QgFQBYCxVX6rb4nUbgThpKxBsLofcSY3d9w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: --7eflzcifipfkwrsh Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH 03/10] userfaultfd.2: comment on feature detection in the example program MIME-Version: 1.0 Hi Axel, On Tue, Sep 19, 2023 at 12:01:59PM -0700, Axel Rasmussen wrote: > The example program doesn't depend on any extra features, so it does not > make use of the two-step feature handshake process. This is fine, but it > might set a bad example for programs which *do* depend on specific > features (e.g. they may conclude they don't need to do anything to > enable / detect them). >=20 > No need to make the example program more complicated: let's just add a > comment indicating why we do it the way we do it in the example, and > describing briefly what a more complicated program would need to do > instead. >=20 > The comment is kept rather brief; a full description of this feature > will be included in ioctl_userfaultfd.2 instead. >=20 > Signed-off-by: Axel Rasmussen Patch applied. Thanks, Alex > --- > man2/userfaultfd.2 | 7 +++++++ > 1 file changed, 7 insertions(+) >=20 > diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 > index 00d94e514..b2b79f61d 100644 > --- a/man2/userfaultfd.2 > +++ b/man2/userfaultfd.2 > @@ -881,6 +881,13 @@ main(int argc, char *argv[]) > if (uffd =3D=3D \-1) > err(EXIT_FAILURE, "userfaultfd"); > \& > + /* NOTE: Two-step feature handshake is not needed here, since this > + example doesn't require any specific features. > + > + Programs that *do* should call UFFDIO_API twice: once with > + `features =3D 0` to detect features supported by this kernel, and > + again with the subset of features the program actually wants to > + enable. */ > uffdio_api.api =3D UFFD_API; > uffdio_api.features =3D 0; > if (ioctl(uffd, UFFDIO_API, &uffdio_api) =3D=3D \-1) > --=20 > 2.42.0.459.ge4e396fd5e-goog >=20 --7eflzcifipfkwrsh Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEE6jqH8KTroDDkXfJAnowa+77/2zIFAmUSGH8ACgkQnowa+77/ 2zJTTxAAlq3w3g9XKdtWdAY0IFZ8OLHqDNS4ORRDwwc6CYY0LLe7lTDsHVO0jDTl Bl4F7WF+OcvPNu9gVwI9Ry8q3uZlOkr6WVi/2wvYV0j6FOmcYf1F4s9mRADGaadZ qvjuQbXsXfV6es4zi1j7HpoJ4mh2UwWyYvzm4HHaiGFCeErkj7JOUPCiIY0YjtCu HZtSMtKEzq8bhawccBa1yKABrKteu/zykDuo620dybqiDivfrvpLwjRJMJ+uZXXQ wis+GPLry0B6ZmfhzIptVQVsm/03bNZU0YrCyGU9VoX/u6W0PqQHRmuedX61F0XI 8BmVBRpEL7F1tdGe6nCUpWmVVHTSAcb24L2hQ6n3eGOWPDNL3wAXbsIy+Vxfa5nY DEkIttpfc4sdfU7UEJ3y/hWkZX/ZKm+CI7opeqkyiw4Qg+sZQGjgudeZ0mSccert xgpsLgPT02ZCEqoEFjAK4z50PSrhVxycja1nbMd5ycUzS7Uy72+izckT16YsFf5b kgvxXo4BEwps4Sfc2yhXejuVwixzvuoBfTR+GXaiLSfyj3ai/No7wtQZPt2myXT2 A7xnYpqfR9ilNaug3ZiXY+e28SAcKWCRM8OpEqIy14RKEzkMhf22zzfE6rBOkQ9g u0wgcrNXyq4RBjKa3tQxnYeB2/3nNgAK8AT2jgKwZZ9XrFfYCCI= =hPpM -----END PGP SIGNATURE----- --7eflzcifipfkwrsh--