linux-kernel - Re: [PATCH v3 2/5] fs: Add fchmodat4()

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Date:   Tue, 11 Jul 2023 16:01:03 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Alexey Gladkov <legion@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, LKML <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
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        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH v3 2/5] fs: Add fchmodat4()

On Tue, Jul 11, 2023 at 02:51:01PM +0200, Alexey Gladkov wrote:
> On Tue, Jul 11, 2023 at 01:52:01PM +0200, Christian Brauner wrote:
> > On Tue, Jul 11, 2023 at 01:42:19PM +0200, Arnd Bergmann wrote:
> > > On Tue, Jul 11, 2023, at 13:25, Alexey Gladkov wrote:
> > > > From: Palmer Dabbelt <palmer@...ive.com>
> > > >
> > > > On the userspace side fchmodat(3) is implemented as a wrapper
> > > > function which implements the POSIX-specified interface. This
> > > > interface differs from the underlying kernel system call, which does not
> > > > have a flags argument. Most implementations require procfs [1][2].
> > > >
> > > > There doesn't appear to be a good userspace workaround for this issue
> > > > but the implementation in the kernel is pretty straight-forward.
> > > >
> > > > The new fchmodat4() syscall allows to pass the AT_SYMLINK_NOFOLLOW flag,
> > > > unlike existing fchmodat.
> > > >
> > > > [1] 
> > > > https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/fchmodat.c;h=17eca54051ee28ba1ec3f9aed170a62630959143;hb=a492b1e5ef7ab50c6fdd4e4e9879ea5569ab0a6c#l35
> > > > [2] 
> > > > https://git.musl-libc.org/cgit/musl/tree/src/stat/fchmodat.c?id=718f363bc2067b6487900eddc9180c84e7739f80#n28
> > > >
> > > > Signed-off-by: Palmer Dabbelt <palmer@...ive.com>
> > > > Signed-off-by: Alexey Gladkov <legion@...nel.org>
> > > 
> > > I don't know the history of why we ended up with the different
> > > interface, or whether this was done intentionally in the kernel
> > > or if we want this syscall.
> > > 
> > > Assuming this is in fact needed, I double-checked that the
> > > implementation looks correct to me and is portable to all the
> > > architectures, without the need for a compat wrapper.
> > > 
> > > Acked-by: Arnd Bergmann <arnd@...db.de>
> > 
> > The system call itself is useful afaict. But please,
> > 
> > s/fchmodat4/fchmodat2/
> 
> Sure. I will.

Thanks. Can you also wire this up for every architecture, please?
I don't see that this has been done in this series.