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Date: Mon, 6 May 2024 20:01:35 -0400
From: Rich Felker <dalias@libc.org>
To: Tony Ambardar <tony.ambardar@gmail.com>
Cc: musl@lists.openwall.com
Message-ID: <20240507000135.GF5341@brightrain.aerifal.cx>
References: <20240421153640.379015-1-Tony.Ambardar@gmail.com>
 <20240423234355.2414567-1-Tony.Ambardar@gmail.com>
 <20240506145056.GG10433@brightrain.aerifal.cx>
 <Zjlq0nlT6POMfWb8@kodidev-ubuntu>
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User-Agent: Mutt/1.5.21 (2010-09-15)
Subject: Re: [musl] [PATCH v2] add renameat2 linux syscall wrapper

On Mon, May 06, 2024 at 04:42:10PM -0700, Tony Ambardar wrote:
> On Mon, May 06, 2024 at 10:50:57AM -0400, Rich Felker wrote:
> > On Tue, Apr 23, 2024 at 04:43:55PM -0700, Tony Ambardar wrote:
> > > This syscall is available since Linux 3.15 and also implemented in glibc
> > > from version 2.28. It is commonly used in filesystem or security contexts.
> > > 
> 
> [SNIP]
> 
> > 
> > If flags is 0, the SYS_renameat syscall is semantically equivalent to
> > the SYS_renameat2 one, so it would be better to just unconditionally
> > do that first rather than failing and falling back.
> > 
> 
> Do you mean rearranging and dropping the ENOSYS conditional, e.g. something
> like below?
> 
> >       int r;
> > #ifdef SYS_renameat
> >       if (!flags) r = __syscall(SYS_renameat, oldfd, old, newfd, new);
> >       else
> > #endif
> >       r = __syscall(SYS_renameat2, oldfd, old, newfd, new, flags);
> >       return __syscall_ret(r);
> 
> Please clarify and I'll update.
> 
> Thanks,
> Tony

Yes, or just (simpler, without any "int r;"):

	if (!flags) return syscall(SYS_renameat, ...);

etc. The use of __syscall and manually calling __syscall_ret is only
helpful if you want to peek/poke at error codes prior to setting errno
and returning.

Rich