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From: Arnd Bergmann <arnd@arndb.de>
To: Martijn Coenen <maco@android.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Michal Marek <michal.lkml@markovi.net>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Oliver Neukum <oneukum@suse.com>, Jessica Yu <jeyu@kernel.org>,
	Stephen Boyd <sboyd@codeaurora.org>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	Sam Ravnborg <sam@ravnborg.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	linux-m68k <linux-m68k@lists.linux-m68k.org>,
	USB list <linux-usb@vger.kernel.org>,
	USB Storage list <usb-storage@lists.one-eyed-alien.net>,
	linux-scsi <linux-scsi@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Martijn Coenen <maco@google.com>,
	Sandeep Patil <sspatil@google.com>,
	Iliyan Malchev <malchev@google.com>,
	Joel Fernandes <joelaf@google.com>
Subject: Re: [PATCH 0/6] Symbol namespaces
Date: Tue, 24 Jul 2018 11:08:21 +0200
Message-ID: <CAK8P3a0SFua3OVzyoWxL+xtozyra5Q5D=GypkOt4hdJ0L3L5Aw@mail.gmail.com> (raw)
In-Reply-To: <CAB0TPYH2G_+faZDcvoEyUmZfwP0j83P0KeZXSJdN9rJ4M1ad3w@mail.gmail.com>

On Tue, Jul 24, 2018 at 10:09 AM, Martijn Coenen <maco@android.com> wrote:
> Hi Arnd,
>
> On Mon, Jul 23, 2018 at 4:28 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>> This looks nice. I don't want to overload you with additional
>> requests, but it might be good to think about how this can
>> be taken further, if we want to actually convert large
>> parts of the kernel to it.
>
> No worries about overloading, I'm happy with all feedback to make this better.
>
>> I have two ideas:
>>
>> - It would be nice to have a simple mechanism in Kconfig
>>   to put all symbols in a module into a namespace that is
>>   derived from KBUILD_MODNAME, to avoid having to
>>   annotate every symbol separately. This could be similar
>>   to how we ended up dealing with EXPORT_NO_SYMBOLS
>>   in the linux-2.4 days, with the goal of eventually having
>>   a namespace for each symbol. Similarly, we could pass
>>   a number of default namespaces through the Makefile,
>>   e.g. if we have a directory that has lots of drivers that all
>>   import the symbols from a common subsystem module.
>
> I'm hinging on two thoughts here; I really like it because it
> obviously reduces work and makes this easier to use. On the other
> hand, you now have to look in multiple places to see if a symbol is
> exported to a namespace/imported from a module. Perhaps it depends on
> how coarse-grained the namespaces end up being. Either way, I think it
> would be pretty easy to cook up patches for this.

Ok, maybe try it and see where we get with it?

>> - If this is possible to implement, it would be great to have
>>   a way to limit the globally visible symbols in a module
>>   to the ones that are explicitly exported  even when a that
>>   module is built-in rather than loadable. Not sure how this
>>   is best done though. A couple of things can be done with
>>   objcopy, or possibly by reintroducing partial linking (which
>>   was removed not too long ago).
>
> If I understand you correctly, this is orthogonal to symbol
> namespaces, right?

Right, the only connection here is that both try to limit the
scope of which symbols are available where. This can definitely
be done without symbol namespaces. The implementation I
had in mind with objcopy might end up using the same
KBUILD_MODNAME as a prefix for internal symbols (which
are not exported to modules), but that is a different problem.

Another related area is the question what happens to symbols
that we want to share between two built-in parts of the kernel
without exporting them to modules. E.g. if we might want to
put all of vfs into one built-in module and make its symbols
private to that module, while all of the mm subsystem is in a
separate built-in module. The symbols that are needed for
communicating between the two could simply be exported
with EXPORT_SYMBOL_GPL(), but we that would open the
surface to loadable modules that can't access them today.
Using namespaces could solve that problem by limiting the
scope in another way, or we could come up with a different
method to annotate them, such as using the gcc visibility
 attributes.

> Do you think these things should be a part of these series, or can it
> be a follow-up?

If you think you can do the first thing easily, I'd say we should
try to come up with an idea of where we want to take this in
the long run. For limiting the scope of global symbols, that may
well be a much bigger task to do upfront, so unless you have an
idea for how to do that, maybe keep it in mind but let's not make
it a dependency.

      Arnd

  reply index

Thread overview: 134+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-16 12:21 Martijn Coenen
2018-07-16 12:21 ` [PATCH 1/6] export: explicitly align struct kernel_symbol Martijn Coenen
2018-07-16 12:21 ` [PATCH 2/6] module: add support for symbol namespaces Martijn Coenen
2018-07-19 16:32   ` Jessica Yu
2018-07-20  7:54     ` Martijn Coenen
2018-07-20 14:49       ` Jessica Yu
2018-07-20 15:42         ` Martijn Coenen
2018-07-23 11:12           ` Jessica Yu
2018-07-24  7:44             ` Martijn Coenen
2018-07-24  7:56   ` Martijn Coenen
2018-07-25 15:55     ` Jessica Yu
2018-07-25 16:48       ` Lucas De Marchi
2018-07-26  7:44         ` Martijn Coenen
2018-07-16 12:21 ` [PATCH 3/6] modpost: add support for checking " Martijn Coenen
2018-07-16 12:21 ` [PATCH 4/6] modpost: add support for generating namespace dependencies Martijn Coenen
2018-07-23  6:49   ` Jessica Yu
2018-07-16 12:21 ` [PATCH 5/6] scripts: Coccinelle script for " Martijn Coenen
2018-07-16 12:21 ` [PATCH 6/6] RFC: USB: storage: move symbols into USB_STORAGE namespace Martijn Coenen
2018-07-17 15:04   ` Alan Stern
2018-07-18 13:28     ` Martijn Coenen
2018-07-16 15:33 ` [PATCH 0/6] Symbol namespaces Greg Kroah-Hartman
2018-07-23 14:28 ` Arnd Bergmann
2018-07-24  8:09   ` Martijn Coenen
2018-07-24  9:08     ` Arnd Bergmann [this message]
2019-08-13 12:16 ` [PATCH v2 0/10] Symbol namespaces - RFC Matthias Maennich
2019-08-13 12:16   ` [PATCH v2 01/10] module: support reading multiple values per modinfo tag Matthias Maennich
2019-08-13 12:40     ` Greg KH
2019-08-13 12:16   ` [PATCH v2 02/10] export: explicitly align struct kernel_symbol Matthias Maennich
2019-08-13 12:41     ` Greg KH
2019-08-13 12:17   ` [PATCH v2 03/10] module: add support for symbol namespaces Matthias Maennich
2019-08-13 15:26     ` Greg KH
2019-08-13 12:17   ` [PATCH v2 04/10] modpost: " Matthias Maennich
2019-08-13 15:27     ` Greg KH
2019-08-13 12:17   ` [PATCH v2 05/10] module: add config option MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS Matthias Maennich
2019-08-13 18:17     ` Greg KH
2019-08-13 20:15     ` Saravana Kannan
2019-08-14 12:54       ` Matthias Maennich
2019-08-14 17:34         ` Saravana Kannan
2019-08-13 12:17   ` [PATCH v2 06/10] export: allow definition default namespaces in Makefiles or sources Matthias Maennich
2019-08-13 18:16     ` Greg KH
2019-08-13 18:16     ` Greg KH
2019-08-13 12:17   ` [PATCH v2 07/10] modpost: add support for generating namespace dependencies Matthias Maennich
2019-08-13 18:21     ` Greg KH
2019-08-13 12:17   ` [PATCH v2 08/10] scripts: Coccinelle script for " Matthias Maennich
2019-08-13 12:31     ` Julia Lawall
2019-08-13 12:44     ` Greg KH
2019-08-14  6:36     ` [Cocci] " Himanshu Jha
2019-08-14  8:03       ` Matthias Maennich
2019-08-15 13:50     ` [v2 " Markus Elfring
2019-08-22  9:18       ` Matthias Maennich
2019-08-22 11:00         ` Markus Elfring
2019-08-13 12:17   ` [PATCH v2 09/10] usb-storage: remove single-use define for debugging Matthias Maennich
2019-08-13 12:42     ` Greg KH
2019-08-13 13:12       ` Greg KH
2019-08-13 12:17   ` [PATCH v2 10/10] RFC: usb-storage: export symbols in USB_STORAGE namespace Matthias Maennich
2019-08-13 12:45     ` Greg KH
2019-08-13 12:47     ` Greg KH
2019-08-13 15:02       ` Matthias Maennich
     [not found]   ` <20190821114955.12788-1-maennich@google.com>
2019-08-21 11:49     ` [PATCH v3 01/11] module: support reading multiple values per modinfo tag Matthias Maennich
2019-08-21 11:49     ` [PATCH v3 02/11] export: explicitly align struct kernel_symbol Matthias Maennich
2019-08-21 11:49     ` [PATCH v3 03/11] module: add support for symbol namespaces Matthias Maennich
2019-08-27 15:37       ` Jessica Yu
2019-08-27 16:04         ` Matthias Maennich
2019-08-21 11:49     ` [PATCH v3 04/11] modpost: " Matthias Maennich
2019-08-26 16:21       ` Jessica Yu
2019-08-27 14:41         ` Matthias Maennich
2019-08-28  9:43           ` Jessica Yu
2019-08-28  9:55             ` Matthias Maennich
2019-08-28 10:16               ` Jessica Yu
2019-08-21 11:49     ` [PATCH v3 05/11] module: add config option MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS Matthias Maennich
2019-08-21 11:49     ` [PATCH v3 06/11] export: allow definition default namespaces in Makefiles or sources Matthias Maennich
2019-08-28 10:49       ` Jessica Yu
2019-08-28 10:56         ` Matthias Maennich
2019-08-21 11:49     ` [PATCH v3 07/11] modpost: add support for generating namespace dependencies Matthias Maennich
2019-08-21 11:49     ` [PATCH v3 08/11] scripts: Coccinelle script for " Matthias Maennich
2019-08-22  6:09       ` [v3 " Markus Elfring
2019-08-29 12:13       ` [PATCH v3 " Jessica Yu
2019-08-21 11:49     ` [PATCH v3 09/11] usb-storage: remove single-use define for debugging Matthias Maennich
2019-08-21 12:37       ` Greg KH
2019-08-21 13:21       ` Thomas Gleixner
2019-08-21 13:32         ` Greg KH
2019-08-21 11:49     ` [PATCH v3 10/11] RFC: usb-storage: export symbols in USB_STORAGE namespace Matthias Maennich
2019-08-21 12:38       ` Greg KH
2019-08-21 14:36         ` Jessica Yu
2019-08-21 23:13       ` Christoph Hellwig
2019-08-22  8:32         ` Matthias Maennich
2019-09-03 15:06 ` [PATCH v4 00/12] Symbol Namespaces Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 01/12] module: support reading multiple values per modinfo tag Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 02/12] export: explicitly align struct kernel_symbol Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 03/12] module: add support for symbol namespaces Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 04/12] modpost: " Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 05/12] module: add config option MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 06/12] export: allow definition default namespaces in Makefiles or sources Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 07/12] modpost: add support for generating namespace dependencies Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 08/12] scripts: Coccinelle script for " Matthias Maennich
2019-09-04  9:53     ` Masahiro Yamada
2019-09-05 14:46       ` Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 09/12] docs: Add documentation for Symbol Namespaces Matthias Maennich
2019-09-04  7:16     ` Greg KH
2019-09-03 15:06   ` [PATCH v4 10/12] usb-storage: remove single-use define for debugging Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 11/12] RFC: usb-storage: export symbols in USB_STORAGE namespace Matthias Maennich
2019-09-03 15:06   ` [PATCH v4 12/12] RFC: watchdog: export core symbols in WATCHDOG_CORE namespace Matthias Maennich
2019-09-03 16:10     ` Guenter Roeck
2019-09-04  8:45       ` Masahiro Yamada
2019-09-04 12:12         ` Guenter Roeck
2019-09-04 16:16           ` [usb-storage] " Matthew Dharm
2019-09-05 10:41             ` Jessica Yu
2019-09-05 10:52               ` Arnd Bergmann
2019-09-05 11:16                 ` Jessica Yu
2019-09-05 11:25                   ` Masahiro Yamada
2019-09-05 12:00                     ` Greg Kroah-Hartman
2019-09-05 11:25               ` Matthias Maennich
2019-09-04  9:37   ` [PATCH v4 00/12] Symbol Namespaces Masahiro Yamada
2019-09-06 10:32 ` [PATCH v5 00/11] " Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 01/11] module: support reading multiple values per modinfo tag Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 02/11] export: explicitly align struct kernel_symbol Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 03/11] module: add support for symbol namespaces Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 04/11] modpost: " Matthias Maennich
2019-09-26 22:24     ` [PATCH] modpost: Copy namespace string into 'struct symbol' Shaun Ruffell
2019-09-27  5:31       ` Greg Kroah-Hartman
2019-09-27  8:03       ` Matthias Maennich
2019-09-30 21:20         ` Shaun Ruffell
2019-10-01 16:19           ` Matthias Maennich
2019-10-01 19:37             ` Shaun Ruffell
2019-09-06 10:32   ` [PATCH v5 05/11] module: add config option MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 06/11] export: allow definition default namespaces in Makefiles or sources Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 07/11] modpost: add support for generating namespace dependencies Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 08/11] scripts: Coccinelle script for " Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 09/11] docs: Add documentation for Symbol Namespaces Matthias Maennich
2019-09-06 10:32   ` [PATCH v5 10/11] usb-storage: remove single-use define for debugging Matthias Maennich
2019-09-06 12:59     ` Jessica Yu
2019-09-06 13:22       ` Greg KH
2019-09-06 10:32   ` [PATCH v5 11/11] usb-storage: export symbols in USB_STORAGE namespace Matthias Maennich
2019-09-09  8:35   ` [PATCH v5 00/11] Symbol Namespaces Jessica Yu

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