linux-kernel - Re: [PATCH] LoongArch: Export some symbols without GPL

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Date:   Wed, 1 Mar 2023 20:08:50 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     WANG Xuerui <kernel@...0n.name>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>, loongarch@...ts.linux.dev,
        linux-arch@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: Export some symbols without GPL

Hi, Xuerui,

On Wed, Mar 1, 2023 at 6:07 PM WANG Xuerui <kernel@...0n.name> wrote:
>
> Hi,
>
> On 2023/3/1 16:51, Huacai Chen wrote:
> > Some symbols, i.e., vm_map_base, empty_zero_page and invalid_pmd_table,
> > could be accessed widely by some out-of-tree non-GPL but important file
> > systems or drivers (e.g., OpenZFS). Let's use EXPORT_SYMBOL() instead of
> > EXPORT_SYMBOL_GPL() to export them, so as to avoid build errors.
>
> The commit title probably could become "Mark 3 symbol exports as non-GPL".
>
> Also you could drop the "some symbols, i.e.," part and go straight to
> the 3 symbols. It sounds more natural to me at least (because I know the
> current wording is 1:1 perfectly idiomatic Chinese, so it is highly
> likely some adjustment would be needed: idiomatic English don't
> *perfectly* map to Chinese).
>
> In addition to this, I've did some archaeology:
>
> In the OpenZFS case, empty_zero_page and vm_map_base are affected.
> vm_map_base is arch/loongarch invention so we actually kind of have
> "authority" over it, but what follows is a little more background on why
> EXPORT_SYMBOL is arguably more appropriate for empty_zero_page.
>
> As it stands today, only 3 architectures export empty_zero_page as a GPL
> symbol: ia64, loongarch and mips. loongarch gets the GPL export by
> inheriting from mips, and the mips export was first introduced in commit
> 497d2adcbf50b ("[MIPS] Export empty_zero_page for sake of the ext4
> module."). The ia64 export was similar: commit a7d57ecf4216e ("[IA64]
> Export three symbols for module use") did so for kvm.
>
> In both ia64 and mips, the export of empty_zero_page was done for
> satisfying some in-kernel component built as module (kvm and ext4
> respectively), and given its reasonably low-level nature, GPL is a
> reasonable choice. But looking at the bigger picture it is evident most
> other architectures do not regard it as GPL, so in effect the symbol
> probably should not be treated as such, in favor of consistency.
>
> You could incorporate some or all of this into the commit message to
> give others some background on the justification. After all reverting
> symbols to non-GPL is relatively rare compared to all the GPL-marking
> actions.
Thank you very much for giving so many backgrounds, I will update the
commit message.

Huacai
>
> >
> > Details about vm_map_base: may be referenced through macros PCI_IOBASE,
> > VMALLOC_START and VMALLOC_END.
> >
> > Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> > ---
> >   arch/loongarch/kernel/cpu-probe.c | 2 +-
> >   arch/loongarch/mm/init.c          | 4 ++--
> >   2 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/loongarch/kernel/cpu-probe.c b/arch/loongarch/kernel/cpu-probe.c
> > index 008b0249905f..001e43dd94ca 100644
> > --- a/arch/loongarch/kernel/cpu-probe.c
> > +++ b/arch/loongarch/kernel/cpu-probe.c
> > @@ -60,7 +60,7 @@ static inline void set_elf_platform(int cpu, const char *plat)
> >
> >   /* MAP BASE */
> >   unsigned long vm_map_base;
> > -EXPORT_SYMBOL_GPL(vm_map_base);
> > +EXPORT_SYMBOL(vm_map_base);
> >
> >   static void cpu_probe_addrbits(struct cpuinfo_loongarch *c)
> >   {
> > diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
> > index e018aed34586..3b7d8129570b 100644
> > --- a/arch/loongarch/mm/init.c
> > +++ b/arch/loongarch/mm/init.c
> > @@ -41,7 +41,7 @@
> >    * don't have to care about aliases on other CPUs.
> >    */
> >   unsigned long empty_zero_page, zero_page_mask;
> > -EXPORT_SYMBOL_GPL(empty_zero_page);
> > +EXPORT_SYMBOL(empty_zero_page);
> >   EXPORT_SYMBOL(zero_page_mask);
> >
> >   void setup_zero_pages(void)
> > @@ -270,7 +270,7 @@ pud_t invalid_pud_table[PTRS_PER_PUD] __page_aligned_bss;
> >   #endif
> >   #ifndef __PAGETABLE_PMD_FOLDED
> >   pmd_t invalid_pmd_table[PTRS_PER_PMD] __page_aligned_bss;
> > -EXPORT_SYMBOL_GPL(invalid_pmd_table);
> > +EXPORT_SYMBOL(invalid_pmd_table);
> >   #endif
> >   pte_t invalid_pte_table[PTRS_PER_PTE] __page_aligned_bss;
> >   EXPORT_SYMBOL(invalid_pte_table);
>
> And in the latter two cases it seems we're actually fixing
> inconsistencies. Nice!
>
> Reviewed-by: WANG Xuerui <git@...0n.name>
>
> --
> WANG "xen0n" Xuerui
>
> Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/
>
>