Commit 747b1f65 authored by Jens Axboe's avatar Jens Axboe
Browse files

iov_iter: overlay struct iovec and ubuf/len 



Add an internal struct iovec that we can return as a pointer, with the
fields of the iovec overlapping with the ITER_UBUF ubuf and length
fields.

Then we can have iter_iov() check for the appropriate type, and return
&iter->__ubuf_iovec for ITER_UBUF and iter->__iov for ITER_IOVEC and
things will magically work out for a single segment request regardless
of either type.

Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent cd0bd57a

include/linux/uio.h

+35 −9
Original line number Diff line number Diff line
@@ -49,7 +49,24 @@ struct iov_iter { 
		size_t iov_offset;

		int last_offset;

	};

	size_t count;

	/*

	 * Hack alert: overlay ubuf_iovec with iovec + count, so

	 * that the members resolve correctly regardless of the type

	 * of iterator used. This means that you can use:

	 *

	 * &iter->__ubuf_iovec or iter->__iov

	 *

	 * interchangably for the user_backed cases, hence simplifying

	 * some of the cases that need to deal with both.

	 */

	union {

		/*

		 * This really should be a const, but we cannot do that without

		 * also modifying any of the zero-filling iter init functions.

		 * Leave it non-const for now, but it should be treated as such.

		 */

		struct iovec __ubuf_iovec;

		struct {

			union {

				/* use iter_iov() to get the current vec */

				const struct iovec *__iov;
@@ -59,6 +76,9 @@ struct iov_iter { 
				struct pipe_inode_info *pipe;

				void __user *ubuf;

			};

			size_t count;

		};

	};

	union {

		unsigned long nr_segs;

		struct {
@@ -69,7 +89,13 @@ struct iov_iter { 
	};

};



#define iter_iov(iter)	(iter)->__iov

static inline const struct iovec *iter_iov(const struct iov_iter *iter)

{

	if (iter->iter_type == ITER_UBUF)

		return (const struct iovec *) &iter->__ubuf_iovec;

	return iter->__iov;

}



#define iter_iov_addr(iter)	(iter_iov(iter)->iov_base + (iter)->iov_offset)

#define iter_iov_len(iter)	(iter_iov(iter)->iov_len - (iter)->iov_offset)