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SubjectRe: [PATCH v5 00/11] Symbol Namespaces
+++ Matthias Maennich [06/09/19 11:32 +0100]:
>As of Linux 5.3-rc7, there are 31207 [1] exported symbols in the kernel.
>That is a growth of roughly 1000 symbols since 4.17 (30206 [2]). There
>seems to be some consensus amongst kernel devs that the export surface
>is too large, and hard to reason about.
>Generally, these symbols fall in one of these categories:
>1) Symbols actually meant for drivers
>2) Symbols that are only exported because functionality is split over
> multiple modules, yet they really shouldn't be used by modules outside
> of their own subsystem
>3) Symbols really only meant for in-tree use
>When module developers try to upstream their code, it regularly turns
>out that they are using exported symbols that they really shouldn't be
>using. This problem is even bigger for drivers that are currently
>out-of-tree, which may be using many symbols that they shouldn't be
>using, and that break when those symbols are removed or modified.
>This patch allows subsystem maintainers to partition their exported
>symbols into separate namespaces, and module authors to import such
>namespaces only when needed.
>This allows subsystem maintainers to more easily limit availability of
>these namespaced symbols to other parts of the kernel. It can also be
>used to partition the set of exported symbols for documentation
>purposes; for example, a set of symbols that is really only used for
>debugging could be in a "SUBSYSTEM_DEBUG" namespace.
>I continued the work mainly done by Martijn Coenen.
>Changes in v2:
>- Rather than adding and evaluating separate sections __knsimport_NS,
> use modinfo tags to declare the namespaces a module introduces.
> Adjust modpost and the module loader accordingly.
>- Also add support for reading multiple modinfo values for the same tag
> to allow list-like access to modinfo tags.
>- The macros in export.h have been cleaned up to avoid redundancy in the
> macro parameters (ns, nspost, nspost2).
>- The introduction of relative references in the ksymtab entries caused
> a rework of the macros to accommodate that configuration as well.
>- Alignment of kernel_symbol in the ksymtab needed to be fixed to allow
> growing the kernel_symbol struct.
>- Modpost does now also append the namespace suffix to the symbol
> entries in Module.symvers.
>- The configuration option MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS allows
> relaxing the enforcement of properly declared namespace imports at
> module loading time.
>- Symbols can be collectively exported into a namespace by defining
> DEFAULT_SYMBOL_NAMESPACE in the corresponding Makefile.
>- The requirement for a very recent coccinelle spatch has been lifted by
> simplifying the script.
>- nsdeps does now ensures MODULE_IMPORT_NS statements are sorted when
> patching the module source files.
>- Some minor bugs have been addressed in nsdeps to allow it to work with
> modules that have more than one source file.
>- The RFC for the usb-storage symbols has been simplified by using
> DEFAULT_SYMBOL_NAMESPACE=USB_STORAGE rather than explicitly exporting
> each and every symbol into that new namespace.
>Changes in v3:
>- Reword the documentation for the
>- Fix printed required version of spatch in coccinelle script.
>- Adopt kbuild changes for modpost: .mod files are no longer generated
> in .tmp_versions. Similarely, generate the .ns_deps files in the tree
> along with the .mod files. Also, nsdeps now uses modules.order as
> source for the list modules to consider.
>- Add an RFC patch to introduce the namespace WATCHDOG_CORE for symbols
> exported in watchdog_core.c.
>Changes in v4:
>- scripts/nsdeps:
> - exit on first error
> - support out-of-tree builds O=...
>- scripts/ update for new Module.symvers format
>- scripts/mod/modpost: make the namespace a separate field when
> exporting to Module.symvers (rather than symbol.NS)
>- include/linux/export.h: fixed style nits
>- kernel/module.c: ensure namespaces are imported before taking a
> reference to the owner module
>- Documentation: document the Symbol Namespace feature and update
> references to Module.symvers and EXPORT_SYMBOL*
>Changes in v5:
>- Makefile: let 'nsdeps' depend on 'modules' to allow
> `make clean; make nsdeps` to work
>- scripts/nsdeps: drop 'exit on first error' again as it just makes more
> problems than it solves
>- drop the watchdog RFC patch for now
>This patch series was developed against v5.3-rc7.

Great work Matthias!

I think this patchset is shaping up nicely. As the merge window is
coming up soon, I'd like to queue this up in modules-next by the end
of today to allow for some testing and "soak" time in linux-next. If
there are any more complaints, please speak up.



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