Further generalise the decompressors by adding a page handler
abstraction. This adds helpers to allow the decompressors
to access and process the output buffers in an implementation
independant manner.
This allows different types of output buffer to be passed
to the decompressors, with the implementation specific
aspects handled at decompression time, but without the
knowledge being held in the decompressor wrapper code.
This will allow the decompressors to handle Squashfs
cache buffers, and page cache pages.
This patch adds the abstraction and an implementation for
the caches.
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Add a multi-threaded decompression implementation which uses
percpu variables.
Using percpu variables has advantages and disadvantages over
implementations which do not use percpu variables.
Advantages:
* the nature of percpu variables ensures decompression is
load-balanced across the multiple cores.
* simplicity.
Disadvantages: it limits decompression to one thread per core.
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
