Re: [RFC PATCH v6] Documentation/arch: Add Documentation/arch-features.txt

Andrew Morton
2015-05-13T22:05:30Z

On Wed, 13 May 2015 09:27:57 -0700 Josh Triplett <josh@joshtriplett.org> wrote:

> If we can't generate this, then the ASCII-art style and right-aligned
> feature names seems *really* likely to produce spurious conflicts,
> especially when adding a feature to the list. Even though it would
> produce a much longer file, would you consider dropping the tables and
> just having a section per feature?

me2. The patch conflicts are going to be pretty bad.

I'd also prefer a format which allows us to add useful notes - it's a
bit hostile to say "thou shalt implement X" without providing any info
about how to do so. Where do we tell maintainers that there's a handy
test app in tools/testing/selftests which they should use?

This way, I can bug patch submitters with "hey, you forgot to update
Documentation/arch-features.txt" and they will add useful info while
it's all still hot in their minds.

And there's a ton of stuff which can go in here, much of it not
immediately apparent.

Just grepping 9 months worth of the stuff I've handled, I'm seeing
things like

HAVE_ARCH_KASAN
__HAVE_ARCH_PMDP_SPLITTING_FLUSH
__HAVE_ARCH_PTE_SPECIAL
__HAVE_ARCH_GATE_AREA
ARCH_HAVE_ELF_ASLR
ARCH_HAS_GCOV_PROFILE_ALL
CONFIG_ARCH_USE_BUILTIN_BSWAP
HAVE_ARCH_HUGE_VMAP
ARCH_HAS_SG_CHAIN
__HAVE_ARCH_STRNCASECMP
ARCH_HAS_ELF_RANDOMIZE
CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID
ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
CONFIG_ARCH_USES_PG_UNCACHED
CONFIG_ARCH_HAS_WALK_MEMORY

and things which don't contain ARCH

HAVE_GENERIC_RCU_GUP
HAVE_RCU_TABLE_FREE
HAVE_GENERIC_RCU_GUP
CONFIG_HAVE_CLK
CONFIG_HAVE_IOREMAP_PROT
CONFIG_HAVE_MEMBLOCK_NODE_MAP

And then there's the increasingly common

arch/include/asm/foo.h:

static inline void wibble(...)
{
...
}
#define wibble wibble

include/linux/foo.h:

#ifndef wibble
static inline void wibble(...)
{
...
}
#define wibble
#endif

which is going to be hard to grep for....

ugh, this thing's going to be enormous. People will go insane reading
it, so each section should have a sentence describing what the feature
does so maintainers can make quick decisions about whether they should
bother.