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From: kevin granade <kevin.granade@gmail.com>
Date: Thu, 2 Dec 2010 14:48:56 -0600
Message-ID: <AANLkTinik7F1=OBnizuQ1Mb4Cya8JKX1Y99AoDZ1Dj-A@mail.gmail.com>
Subject: Re: [PATCH 1/8] Add yaffs2 file system: allocator, attribs, bitmap code
To: Ryan Mallon <ryan@bluewatersys.com>
Cc: Charles Manning <cdhmanning@gmail.com>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Thu, Dec 2, 2010 at 1:49 PM, Ryan Mallon <ryan@bluewatersys.com> wrote:
> On 12/01/2010 10:57 AM, Charles Manning wrote:
>> Signed-off-by: Charles Manning <cdhmanning@gmail.com>
>> ---
>> ?fs/yaffs2/yaffs_allocator.c | ?397 +++++++++++++++++++++++++++++++++++++++++++
>> ?fs/yaffs2/yaffs_allocator.h | ? 30 ++++
>> ?fs/yaffs2/yaffs_attribs.c ? | ?124 ++++++++++++++
>> ?fs/yaffs2/yaffs_attribs.h ? | ? 28 +++
>> ?fs/yaffs2/yaffs_bitmap.c ? ?| ?104 +++++++++++
>> ?fs/yaffs2/yaffs_bitmap.h ? ?| ? 33 ++++
>> ?6 files changed, 716 insertions(+), 0 deletions(-)
>> ?create mode 100644 fs/yaffs2/yaffs_allocator.c
>> ?create mode 100644 fs/yaffs2/yaffs_allocator.h
>> ?create mode 100644 fs/yaffs2/yaffs_attribs.c
>> ?create mode 100644 fs/yaffs2/yaffs_attribs.h
>> ?create mode 100644 fs/yaffs2/yaffs_bitmap.c
>> ?create mode 100644 fs/yaffs2/yaffs_bitmap.h
>>
>> diff --git a/fs/yaffs2/yaffs_allocator.c b/fs/yaffs2/yaffs_allocator.c
>> new file mode 100644
>> index 0000000..b9fe31e
>> --- /dev/null
>> +++ b/fs/yaffs2/yaffs_allocator.c
>> @@ -0,0 +1,397 @@
>> +/*
>> + * YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
>> + *
>> + * Copyright (C) 2002-2010 Aleph One Ltd.
>> + * ? for Toby Churchill Ltd and Brightstar Engineering
>> + *
>> + * Created by Charles Manning <charles@aleph1.co.uk>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#include "yaffs_allocator.h"
>> +#include "yaffs_guts.h"
>> +#include "yaffs_trace.h"
>> +#include "yportenv.h"
>> +
>> +#ifdef CONFIG_YAFFS_YMALLOC_ALLOCATOR
>
> This doesn't appear to be defined anywhere and is not in Kconfig. Is
> this just a wrapper for support on other operating systems or does it
> can it be used on Linux for debugging? In the former case it should
> probably removed and in the latter it should probably have a comment
> explaining why you would want to define it.
>
> <snip>
>
>> +
>> +#include "yaffs_bitmap.h"
>> +#include "yaffs_trace.h"
>> +/*
>> + * Chunk bitmap manipulations
>> + */
>> +
>> +static Y_INLINE u8 *yaffs_block_bits(struct yaffs_dev *dev, int blk)
>
> Should just use inline.
>
> <snip>
>
>> +
>> +int yaffs_still_some_chunks(struct yaffs_dev *dev, int blk)
>> +{
>> + ? ? u8 *blk_bits = yaffs_block_bits(dev, blk);
>> + ? ? int i;
>> + ? ? for (i = 0; i < dev->chunk_bit_stride; i++) {
>
> Nitpick: You should have a blank line between variable declarations and
> start of code.
>
> <snip>
>
>> +int yaffs_count_chunk_bits(struct yaffs_dev *dev, int blk)
>> +{
>> + ? ? u8 *blk_bits = yaffs_block_bits(dev, blk);
>> + ? ? int i;
>> + ? ? int n = 0;
>> + ? ? for (i = 0; i < dev->chunk_bit_stride; i++) {
>> + ? ? ? ? ? ? u8 x = *blk_bits;
>> + ? ? ? ? ? ? while (x) {
>> + ? ? ? ? ? ? ? ? ? ? if (x & 1)
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? n++;
>> + ? ? ? ? ? ? ? ? ? ? x >>= 1;
>> + ? ? ? ? ? ? }
>> +
>> + ? ? ? ? ? ? blk_bits++;
>> + ? ? }
>> + ? ? return n;
>> +}
>
>
> This is possibly more concise as a for loop. Also moving the definitions
> all to the top of the file and combining same types definitions on one
> line reduces this function to:
>
> int yaffs_count_chunk_bits(struct yaffs_dev *dev, int blk)
> {
> ? ? ? ?u8 x, *blk_bits = yaffs_block_bits(dev, blk);
> ? ? ? ?int i, n = 0;
>
> ? ? ? ?for (i = 0; i < dev->chunk_bit_stride; i++, blk_bits++)
> ? ? ? ? ? ? ? ?for (x = *blk_bits; x; x >>= 1)
> ? ? ? ? ? ? ? ? ? ? ? ?if (x & 1)
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?n++;
>
> ? ? ? ?return n;
> }

Actually, how about using the standard hamming weight function?
This adds a dependency on linux/bitops.h, but seems to be carefully
crafted to be as fast as possible based on the available hardware.

int yaffs_count_chunk_bits(struct yaffs_dev *dev, int blk)
{
       u8 *blk_bits = yaffs_block_bits(dev, blk);
       int i, n = 0;

       for (i = 0; i < dev->chunk_bit_stride; i++, blk_bits++)
               n += hweight8(*blk_bits);

       return n;
}

Kevin Granade


>
> ~Ryan
>
> --
> Bluewater Systems Ltd - ARM Technology Solution Centre
>
> Ryan Mallon ? ? ? ? ? ? ? ? ? ? 5 Amuri Park, 404 Barbadoes St
> ryan@bluewatersys.com ? ? ? ? ? PO Box 13 889, Christchurch 8013
> http://www.bluewatersys.com ? ? New Zealand
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