linux-kernel - Re: [PATCH 1/2] uapi: split openat2(2) definitions from fcntl.h

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Date:   Fri, 20 Dec 2019 20:31:53 +1100
From:   Aleksa Sarai <cyphar@...har.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Florian Weimer <fweimer@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Shuah Khan <shuah@...nel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        "dev@...ncontainers.org" <dev@...ncontainers.org>,
        "containers@...ts.linux-foundation.org" 
        <containers@...ts.linux-foundation.org>,
        "libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 1/2] uapi: split openat2(2) definitions from fcntl.h

On 2019-12-19, David Laight <David.Laight@...LAB.COM> wrote:
> From: Aleksa Sarai
> > Sent: 19 December 2019 13:45
> > On 2019-12-19, Florian Weimer <fweimer@...hat.com> wrote:
> > > * Aleksa Sarai:
> > >
> > > > diff --git a/include/uapi/linux/openat2.h b/include/uapi/linux/openat2.h
> > > > new file mode 100644
> > > > index 000000000000..19ef775e8e5e
> > > > --- /dev/null
> > > > +++ b/include/uapi/linux/openat2.h
> > > > @@ -0,0 +1,41 @@
> > > > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > > > +#ifndef _UAPI_LINUX_OPENAT2_H
> > > > +#define _UAPI_LINUX_OPENAT2_H
> > >
> > > I think you should include the relevant header for __align_u64
> > > etc. here.
> > 
> > Right -- no idea why I forgot to include them.
> 
> I'm guessing that is just 64bit aligned on 32bit archs like x86?

Yeah,

#define __aligned_u64 __u64 __attribute__((aligned(8)))

> No need to enforce it provided the structure will have no padding on
> archs where the 64bit fields are 64bit aligned. A plain __u64 should
> be fine.

Will this cause problems for x86-on-x86_64 emulation? Requiring an
8-byte alignment for 'struct open_how' really isn't that undue of a
burden IMHO. Then again, clone3 is a bit of an outlier since both
perf_event_open and sched_setattr just use __u64s.

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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