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

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Message-ID: <fc373999-466d-4587-b049-9f90076b4bd0@t-8ch.de>
Date:   Sat, 4 Nov 2023 18:32:57 +0100
From:   Thomas Weißschuh <linux@...ssschuh.net>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Willy Tarreau <w@....eu>, 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 2023-11-04 18:07:21+0100, Greg Kroah-Hartman wrote:
> 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.

It seems to be _BITUL() and _BITULL() from include/uapi/linux/const.h.

But first we'd need to figure out if we he can drop the pvpanic.h uapi
header. I hoped you could give a definitive answer for that.
Personally I'd hate to break stuff for qemu.


Thomas