Re: [PATCH 0/4] lib: rework bitmap_parse

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Sat, Apr 27, 2019 at 08:29:30PM -0700, Yury Norov wrote:
> On top of next-20190418.
> 
> Similarly to recently revisited bitmap_parselist() [1],
> bitmap_parse() is ineffective and overcomplicated.  This
> series reworks it, aligns its interface with bitmap_parselist()
> and makes usage simpler.
> 
> The series also adds a test for the function and fixes usage of it
> in cpumask_parse() according to new design - drops the calculating
> of length of an input string.
> 
> The following users would also consider to drop the length argument,
> if possible:
> drivers/block/drbd/drbd_main.c:2608
> kernel/padata.c:924
> net/core/net-sysfs.c:726
> net/core/net-sysfs.c:1309
> net/core/net-sysfs.c:1391
> 
> bitmap_parse() takes the array of numbers to be put into the map in
> the BE order which is reversed to the natural LE order for bitmaps.
> For example, to construct bitmap containing a bit on the position 42,
> we have to put a line '400,0'. Current implementation reads chunk
> one by one from the beginning ('400' before '0') and makes bitmap
> shift after each successful parse. It makes the complexity of the
> whole process as O(n^2). We can do it in reverse direction ('0'
> before '400') and avoid shifting, but it requires reverse parsing
> helpers.

Shouldn't test ceases pass on existing code base? I would rather start series
with enabling tests and then we will have a proof that before and after at
least tests have not been broken.

> 
> Tested on arm64 and BE mips.
> 
> [1] https://lkml.org/lkml/2019/4/16/66
> 
> Yury Norov (6):
>   lib/string: add strnchrnul()
>   bitops: more BITS_TO_* macros
>   lib/bitmap: make bitmap_parse_user a wrapper on bitmap_parse
>   lib: rework bitmap_parse()
>   lib: add test for bitmap_parse()
>   cpumask: don't calculate length of the input string
> 
>  include/linux/bitmap.h       |   8 +-
>  include/linux/bitops.h       |   3 +
>  include/linux/cpumask.h      |   4 +-
>  include/linux/string.h       |   3 +
>  lib/bitmap.c                 | 197 +++++++++++++++++------------------
>  lib/string.c                 |  20 ++++
>  lib/test_bitmap.c            | 102 +++++++++++++++++-
>  tools/include/linux/bitops.h |   9 +-
>  8 files changed, 230 insertions(+), 116 deletions(-)
> 
> -- 
> 2.17.1
> 

-- 
With Best Regards,
Andy Shevchenko