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btrfs: refactor extent buffer bitmaps operations
[BACKGROUND]
Currently we handle extent bitmaps manually in
extent_buffer_bitmap_set() and extent_buffer_bitmap_clear().
Although with various helpers like eb_bitmap_offset() it's still a little
messy to read. The code seems to be a copy of bitmap_set(), but with
all the cross-page handling embedded into the code.
[ENHANCEMENT]
This patch would enhance the readability by introducing two helpers:
- memset_extent_buffer()
To handle the byte aligned range, thus all the cross-page handling is
done there.
- extent_buffer_get_byte()
This for the first and the last byte operations, which only need to
grab one byte, thus no need for any cross-page handling.
So we can split both extent_buffer_bitmap_set() and
extent_buffer_bitmap_clear() into 3 parts:
- Handle the first byte
If the range fits inside the first byte, we can exit early.
- Handle the byte aligned part
This is the part which can have cross-page operations, and it would
be handled by memset_extent_buffer().
- Handle the last byte
This refactoring does not only make the code a little easier to read,
but also makes later folio/page switch much easier, as the switch only
needs to be done inside memset_extent_buffer() and extent_buffer_get_byte().
Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>