[PATCH 02/14] fs: introduce iomap infrastructure

[Bob Peterson]

----- Original Message -----
> Add infrastructure for multipage buffered writes.  This is implemented
> using an main iterator that applies an actor function to a range that
> can be written.
> 
> This infrastucture is used to implement a buffered write helper, one
> to zero file ranges and one to implement the ->page_mkwrite VM
> operations.  All of them borrow a fair amount of code from fs/buffers.
> for now by using an internal version of __block_write_begin that
> gets passed an iomap and builds the corresponding buffer head.
> 
> The file system is gets a set of paired ->iomap_begin and ->iomap_end
> calls which allow it to map/reserve a range and get a notification
> once the write code is finished with it.
> 
> Based on earlier code from Dave Chinner.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
> +		/*
> +		 * For unwritten regions, we always need to ensure that
> +		 * sub-block writes cause the regions in the block we are not
> +		 * writing to are zeroed. Set the buffer as new to ensre this.

Minor typo: s/ensre/ensure/ above.

Reviewed-off-by: Bob Peterson <rpeterso at redhat.com>