Re: [PATCH 02/10] btrfs-progs: Add extent buffer bitmap manipulation infrastructure

[Omar Sandoval <osandov@osandov.com>]

On Mon, Oct 01, 2018 at 05:46:13PM +0300, Nikolay Borisov wrote:
> Those functions are in preparation for adding the freespace tree
> repair code since it needs to be able to deal with bitmap based fsts.
> This patch adds extent_buffer_bitmap_set and extent_buffer_bitmap_clear
> functions. Since in userspace we don't have to deal with page mappings
> their implementation is vastly simplified by simply setting each bit in
> the passed range.

Reviewed-by: Omar Sandoval <osandov@fb.com>

> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  extent_io.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  extent_io.h |  4 ++++
>  2 files changed, 60 insertions(+)
> 
> diff --git a/extent_io.c b/extent_io.c
> index 198492699438..de47c2c59ae9 100644
> --- a/extent_io.c
> +++ b/extent_io.c
> @@ -204,6 +204,62 @@ static int clear_state_bit(struct extent_io_tree *tree,
>  	return ret;
>  }
>  
> +/**
> + * extent_buffer_bitmap_set - set an area of a bitmap
> + * @eb: the extent buffer
> + * @start: offset of the bitmap item in the extent buffer
> + * @pos: bit number of the first bit
> + * @len: number of bits to set
> + */
> +void extent_buffer_bitmap_set(struct extent_buffer *eb, unsigned long start,
> +                              unsigned long pos, unsigned long len)
> +{
> +	u8 *p = (u8 *)eb->data + start + BIT_BYTE(pos);
> +	const unsigned int size = pos + len;
> +	int bits_to_set = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
> +	u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(pos);
> +
> +	while (len >= bits_to_set) {
> +		*p |= mask_to_set;
> +		len -= bits_to_set;
> +		bits_to_set = BITS_PER_BYTE;
> +		mask_to_set = ~0;
> +		p++;
> +	}
> +	if (len) {
> +		mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
> +		*p |= mask_to_set;
> +	}
> +}
> +
> +
> +/**
> + * extent_buffer_bitmap_clear - clear an area of a bitmap
> + * @eb: the extent buffer
> + * @start: offset of the bitmap item in the extent buffer
> + * @pos: bit number of the first bit
> + * @len: number of bits to clear
> + */
> +void extent_buffer_bitmap_clear(struct extent_buffer *eb, unsigned long start,
> +                                unsigned long pos, unsigned long len)
> +{
> +	u8 *p = (u8 *)eb->data + start + BIT_BYTE(pos);
> +	const unsigned int size = pos + len;
> +	int bits_to_clear = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
> +	u8 mask_to_clear = BITMAP_FIRST_BYTE_MASK(pos);
> +
> +	while (len >= bits_to_clear) {
> +		*p &= ~mask_to_clear;
> +		len -= bits_to_clear;
> +		bits_to_clear = BITS_PER_BYTE;
> +		mask_to_clear = ~0;
> +		p++;
> +	}
> +	if (len) {
> +		mask_to_clear &= BITMAP_LAST_BYTE_MASK(size);
> +		*p &= ~mask_to_clear;
> +	}
> +}
>  /*
>   * clear some bits on a range in the tree.
>   */
> diff --git a/extent_io.h b/extent_io.h
> index d407d93d617e..b67c6fc40e89 100644
> --- a/extent_io.h
> +++ b/extent_io.h
> @@ -175,4 +175,8 @@ int read_data_from_disk(struct btrfs_fs_info *info, void *buf, u64 offset,
>  			u64 bytes, int mirror);
>  int write_data_to_disk(struct btrfs_fs_info *info, void *buf, u64 offset,
>  		       u64 bytes, int mirror);
> +void extent_buffer_bitmap_clear(struct extent_buffer *eb, unsigned long start,
> +                                unsigned long pos, unsigned long len);
> +void extent_buffer_bitmap_set(struct extent_buffer *eb, unsigned long start,
> +                              unsigned long pos, unsigned long len);
>  #endif
> -- 
> 2.7.4
>