Messages in this thread | | | From | Masahiro Yamada <> | Date | Tue, 31 May 2022 16:44:21 +0900 | Subject | Re: [PATCH v2] export: fix string handling of namespace in EXPORT_SYMBOL_NS |
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On Tue, May 24, 2022 at 5:10 PM Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > > 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@linuxfoundation.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@linuxfoundation.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.
Kbuild provides a macro "stringify"
It shall be converted to:
subdir-ccflags-y += -DANDROID_GKI_VFS_EXPORT_ONLY=$(call stringify,VFS_internal_I_am_really_a_filesystem_and_am_NOT_a_driver)
> > 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?
Yes, that is an alternative.
> 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?
Right, the compiler does not complain about a space in the namespace. We can check it in modpost if we like.
BTW, do we need EXPORT_SYMBOL_NS() in the first place?
If you think DEFAULT_SYMBOL_NAMESPACE is useful, you have already noticed that the per-module namespace is more convenient than the per-symbol namespace.
For example, if you look at drivers/hwmon/pmbus/pmbus_core.c, all symbols are exported by EXPORT_SYMBOL_NS_GPL(... , PMBUS). I do not see any module that exports multiple namespaces.
So, I think per-module namespace control is enough.
[Deprecate] EXPORT_SYMBOL_NS(<symbol>, <namespace>) EXPORT_SYMBOL_NS_GPL(<symbol>, <namespace>)
[Add] MODULE_NAMESPACE(<namespace>)
If MODULE_NAMESPACE(<namespace>) is added to a module, all symbols exported from that module belong to <namespace>.
> thanks, > > greg k-h
-- Best Regards Masahiro Yamada
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