linux-kernel - Re: [PATCH v2] export: fix string handling of namespace in EXPORT_SYMBOL

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Date:   Tue, 24 May 2022 10:10:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Jessica Yu <jeyu@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        Matthias Maennich <maennich@...gle.com>
Subject: Re: [PATCH v2] export: fix string handling of namespace in
 EXPORT_SYMBOL_NS

On Tue, May 24, 2022 at 03:31:59AM +0900, Masahiro Yamada wrote:
> On Wed, Apr 27, 2022 at 11:50 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Wed, Apr 27, 2022 at 11:29:19PM +0900, Masahiro Yamada wrote:
> > > On Wed, Apr 27, 2022 at 6:06 PM Greg Kroah-Hartman
> > > <gregkh@...uxfoundation.org> wrote:
> > > >
> > > > Commit c3a6cf19e695 ("export: avoid code duplication in
> > > > include/linux/export.h") broke the ability for a defined string to be
> > > > used as a namespace value.
> > >
> > > In hindsight, this was a bad idea.
> > >
> > >
> > > EXPORT_SYMBOL_NS_GPL(dw_spi_resume_host, "SPI_DW_CORE")
> > >
> > >    is much much better than:
> > >
> > > EXPORT_SYMBOL_NS_GPL(dw_spi_resume_host, SPI_DW_CORE)
> >
> > I agree, but it's really not that big of a deal.  We could change it if
> > you want.
> >
> > > ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=USB_STORAGE
> > >
> > > is also a bad idea.
> >
> > That's not such a bad idea as it lets you set a namespace for a
> > directory and below easily.  What would you want to use instead?
> >
> > > When you look at EXPORT_SYMBOL_GPL() in C files, you will not be
> > > aware of the presence of the namespace.
> >
> > It's easy to tell when things do not link properly :)
> >
> > > Anyway, it is presumably too late to fix it.
> >
> > Not really, the number of in-kernel users are still small and can be
> > changed if you like.  External users can update when they hit the change
> > as well, not a big deal.
> 
> 
> If I send a patch for global conversion,
> will you be happy to pick it up?
> 
> 
> I think this should be applied at the very last moment
> of the MW.

Make up a patch right after -rc1 to get into -rc2 as that's usually the
best time for tree-wide changes like this.

> I can convert tree-wide by sed.
> 
> 
> Example of conversion:
> 
> EXPORT_SYMBOL_NS_GPL(dw_spi_resume_host, SPI_DW_CORE)
>    -->
> EXPORT_SYMBOL_NS_GPL(dw_spi_resume_host, "SPI_DW_CORE")

Ah, but then this breaks my use case where I did in the Android tree:

	EXPORT_SYMBOL_NS_GPL(symbol_name, ANDROID_GKI_VFS_EXPORT_ONLY);

and then in the makefile I did:
	subdir-ccflags-y += -DANDROID_GKI_VFS_EXPORT_ONLY=VFS_internal_I_am_really_a_filesystem_and_am_NOT_a_driver

That saved me typing a lot of "VFS_internal_I_am..." in the .c files.

I know out-of-tree stuff does not matter, but a simple way to make this
work would be nice.

I could just do:
	#define ANDROID_GKI_VFS_EXPORT_ONLY	"VFS_internal_I_am..."
in a .c file which would handle this, right?

Ok, so maybe that isn't an issue, nevermind...

But, if we have a string here, what happens if someone puts a space in
it:
	EXPORT_SYMBOL_NS_GPL(symbol_name, "MY DRIVER NAMESPACE");
that will not break the build but will cause the tools to really
complain, right?  Or do the wrong thing and put them in the "MY"
namespace?

thanks,

greg k-h