[PATCH 02/14] fs: introduce iomap infrastructure

[Jan Kara]

On Wed 01-06-16 16:44:45, Christoph Hellwig wrote:
> 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>
> Reviewed-by: Bob Peterson <rpeterso at redhat.com>

When reading through the patch I've noticed two minor errors in the
comments:

...
> +static loff_t
> +iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
> +		struct iomap_ops *ops, void *data, iomap_actor_t actor)
> +{
> +	struct iomap iomap = { 0 };
> +	loff_t written = 0, ret;
> +
> +	/*
> +	 * Need to map a range from start position for count bytes. This can
						       ^^^^ length
...

>  struct iomap {
> -	sector_t	blkno;	/* first sector of mapping */
> -	loff_t		offset;	/* file offset of mapping, bytes */
> -	u64		length;	/* length of mapping, bytes */
> -	int		type;	/* type of mapping */
> +	sector_t		blkno;	/* first sector of mapping, fs blocks */

This is actually in 512-byte units, not in fs blocks as the comment
suggests, right?

								Honza
-- 
Jan Kara <jack at suse.com>
SUSE Labs, CR