Date: Thu, 24 Aug 2023 13:29:06 -0600 From: Warner Losh <imp@bsdimp.com> To: John Baldwin <jhb@freebsd.org> Cc: Jessica Clarke <jrtc27@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "dev-commits-src-all@freebsd.org" <dev-commits-src-all@freebsd.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@freebsd.org> Subject: Re: git: 4a69fc16a583 - main - Add membarrier(2) Message-ID: <CANCZdfq7y2RxtMNF7stt1hSbwqEWsia3muy4nT0oqwaCOv=maA@mail.gmail.com> In-Reply-To: <747e34d5-8191-5fb9-deb4-c94d7f1693e0@FreeBSD.org> References: <202308230007.37N07cOK082906@gitrepo.freebsd.org> <748B7A01-5011-44EE-BB04-282AE96F9B5B@freebsd.org> <ZOVxDqInEgUhBaIN@kib.kiev.ua> <0F3EA94D-6696-471C-ABF6-840B5E92967F@freebsd.org> <CANCZdfpqJM4dsyEFJt6P_Yf9WBJ9V3hYe8tVCipJr0pecsHekg@mail.gmail.com> <747e34d5-8191-5fb9-deb4-c94d7f1693e0@FreeBSD.org>
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--0000000000007190d10603b03e8c Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Aug 24, 2023 at 10:19=E2=80=AFAM John Baldwin <jhb@freebsd.org> wro= te: > On 8/23/23 6:01 AM, Warner Losh wrote: > > On Tue, Aug 22, 2023 at 11:37=E2=80=AFPM Jessica Clarke <jrtc27@freebsd= .org> > wrote: > > > >> > >>> The addition does not change any existing code path in the kernel. > >> > >> No, but it commits us to a new syscall being stable just days before 1= 4 > >> branches and has its ABI frozen. > >> > > > > I'd planned on committing timerfd later today. I didn't consider it an > ABI > > breakage, since it was just additive. It's one of the things that can b= e > > MFC'd (we don't prohibit new system calls). > > (Not taking a side on the merits of the current membarrier(2) > implementation) > > I think Jess's point here is not that a new syscall is not a valid ABI > breakage, but more that once you add a new syscall that makes it into a > release, now the ABI of that syscall is frozen and can't be changed. Tha= t > said, syscall numbers are relatively "cheap", so if we had to renumber > membarrier(2) because its ABI was found to be a problem that could be don= e, > albeit at the cost of keeping the old one around under COMPAT_FREEBSD<n>. > OK. I jumped to the wrong conclusion... Good points all around. Warner --0000000000007190d10603b03e8c Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote">= <div dir=3D"ltr" class=3D"gmail_attr">On Thu, Aug 24, 2023 at 10:19=E2=80= =AFAM John Baldwin <<a href=3D"mailto:jhb@freebsd.org">jhb@freebsd.org</= a>> wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0p= x 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On= 8/23/23 6:01 AM, Warner Losh wrote:<br> > On Tue, Aug 22, 2023 at 11:37=E2=80=AFPM Jessica Clarke <<a href=3D= "mailto:jrtc27@freebsd.org" target=3D"_blank">jrtc27@freebsd.org</a>> wr= ote:<br> > <br> >><br> >>> The addition does not change any existing code path in the ker= nel.<br> >><br> >> No, but it commits us to a new syscall being stable just days befo= re 14<br> >> branches and has its ABI frozen.<br> >><br> > <br> > I'd planned on committing timerfd later today. I didn't consid= er it an ABI<br> > breakage, since it was just additive. It's one of the things that = can be<br> > MFC'd (we don't prohibit new system calls).<br> <br> (Not taking a side on the merits of the current membarrier(2) implementatio= n)<br> <br> I think Jess's point here is not that a new syscall is not a valid ABI<= br> breakage, but more that once you add a new syscall that makes it into a<br> release, now the ABI of that syscall is frozen and can't be changed.=C2= =A0 That<br> said, syscall numbers are relatively "cheap", so if we had to ren= umber<br> membarrier(2) because its ABI was found to be a problem that could be done,= <br> albeit at the cost of keeping the old one around under COMPAT_FREEBSD<n&= gt;.<br></blockquote><div><br></div><div>OK. I jumped to the wrong conclusi= on...=C2=A0 Good points all around.</div><div><br></div><div><br></div><div= >Warner</div></div></div> --0000000000007190d10603b03e8c--
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