[PATCH] splice: add comments documenting more of the code

	loff_t pos;			/* file position */

};

/*

 * Attempt to steal a page from a pipe buffer. This should perhaps go into

 * a vm helper function, it's already simplified quite a bit by the

 * addition of remove_mapping(). If success is returned, the caller may

 * attempt to reuse this page for another destination.

 */

static int page_cache_pipe_buf_steal(struct pipe_inode_info *info,

				     struct pipe_buffer *buf)

{

	.steal = page_cache_pipe_buf_steal,

};

/*

 * Pipe output worker. This sets up our pipe format with the page cache

 * pipe buffer operations. Otherwise very similar to the regular pipe_writev().

 */

static ssize_t move_to_pipe(struct inode *inode, struct page **pages,

			    int nr_pages, unsigned long offset,

			    unsigned long len, unsigned int flags)

	return move_to_pipe(pipe, pages, i, offset, len, flags);

}

/**

 * generic_file_splice_read - splice data from file to a pipe

 * @in:		file to splice from

 * @pipe:	pipe to splice to

 * @len:	number of bytes to splice

 * @flags:	splice modifier flags

 *

 * Will read pages from given file and fill them into a pipe.

 *

 */

ssize_t generic_file_splice_read(struct file *in, struct inode *pipe,

				 size_t len, unsigned int flags)

{

 *	- Destination page does not exist, we can add the pipe page to

 *	  the page cache and avoid the copy.

 *

 * For now we just do the slower thing and always copy pages over, it's

 * easier than migrating pages from the pipe to the target file. For the

 * case of doing file | file splicing, the migrate approach had some LRU

 * nastiness...

 * If asked to move pages to the output file (SPLICE_F_MOVE is set in

 * sd->flags), we attempt to migrate pages from the pipe to the output

 * file address space page cache. This is possible if no one else has

 * the pipe page referenced outside of the pipe and page cache. If

 * SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create

 * a new page in the output file page cache and fill/dirty that.

 */

static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,

			struct splice_desc *sd)

	 * reuse buf page, if SPLICE_F_MOVE is set

	 */

	if (sd->flags & SPLICE_F_MOVE) {

		/*

		 * If steal succeeds, buf->page is now pruned from the vm

		 * side (LRU and page cache) and we can reuse it.

		 */

		if (buf->ops->steal(info, buf))

			goto find_page;

typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,

			   struct splice_desc *);

/*

 * Pipe input worker. Most of this logic works like a regular pipe, the

 * key here is the 'actor' worker passed in that actually moves the data

 * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.

 */

static ssize_t move_from_pipe(struct inode *inode, struct file *out,

			      size_t len, unsigned int flags,

			      splice_actor *actor)

}

/**

 * generic_file_splice_write - splice data from a pipe to a file

 * @inode:	pipe inode

 * @out:	file to write to

 * @len:	number of bytes to splice

 * @flags:	splice modifier flags

 *

 * Will either move or copy pages (determined by @flags options) from

 * the given pipe inode to the given file.

 *

 */

ssize_t generic_file_splice_write(struct inode *inode, struct file *out,

				  size_t len, unsigned int flags)

{

	return ret;

}

/**

 * generic_splice_sendpage - splice data from a pipe to a socket

 * @inode:	pipe inode

 * @out:	socket to write to

 * @len:	number of bytes to splice

 * @flags:	splice modifier flags

 *

 * Will send @len bytes from the pipe to a network socket. No data copying

 * is involved.

 *

 */

ssize_t generic_splice_sendpage(struct inode *inode, struct file *out,

				size_t len, unsigned int flags)

{

EXPORT_SYMBOL(generic_file_splice_write);

EXPORT_SYMBOL(generic_file_splice_read);

/*

 * Attempt to initiate a splice from pipe to file.

 */

static long do_splice_from(struct inode *pipe, struct file *out, size_t len,

			   unsigned int flags)

{

	return out->f_op->splice_write(pipe, out, len, flags);

}

/*

 * Attempt to initiate a splice from a file to a pipe.

 */

static long do_splice_to(struct file *in, struct inode *pipe, size_t len,

			 unsigned int flags)

{

	return in->f_op->splice_read(in, pipe, len, flags);

}

/*

 * Determine where to splice to/from.

 */

static long do_splice(struct file *in, struct file *out, size_t len,

		      unsigned int flags)

{