linux-kernel - Re: [PATCH RFC] misc/pvpanic: add support for normal shutdowns

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Message-ID: <2023110418-unreached-smith-5625@gregkh>
Date:   Sat, 4 Nov 2023 18:07:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Willy Tarreau <w@....eu>
Cc:     Thomas Weißschuh <linux@...ssschuh.net>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Zhangjin Wu <falcon@...ylab.org>,
        Yuan Tan <tanyuan@...ylab.org>
Subject: Re: [PATCH RFC] misc/pvpanic: add support for normal shutdowns

On Sat, Nov 04, 2023 at 02:56:34PM +0100, Willy Tarreau wrote:
> On Sat, Nov 04, 2023 at 02:53:37PM +0100, Thomas Weißschuh wrote:
> > > > The real reason probably doesn't matter today as the header propably
> > > > can't be dropped from Linux anyways for compatibility reasons.
> > > > 
> > > > > And if they need to be here, why not use the proper BIT() macro for it?
> > > > 
> > > > This was for uniformity with the existing code.
> > > > I can send a (standalone?) patch to fix it up.
> > > 
> > > If we keep it, sure, that would be nice.  But let's try to drop it if
> > > possible :)
> > 
> > It will break the mentioned scripts/update-linux-headers.sh from qemu.
> > 
> > 
> > Note:
> > 
> > BIT() is part of include/vdso/bits.h which is not part of the
> > uapi. How is it supposed to work?
> > Some other uapi header also use BIT() but that seems to work by accident
> > as the users have the macro defined themselves.
> 
> Be careful here, we don't want to expose this kernel macro to userland,
> it would break programs that define their own (possibly different) BIT
> macro. BIT() is used in kernel headers but we should not presume that
> it is available from userland.

It's already there :(

I thought we had a uapi-safe version somewhere, but I can't seem to find
it anymore, so I don't remember what it is called.

thanks,

greg k-h