Commit 27c0e374 authored by Al Viro's avatar Al Viro
Browse files

[iov_iter] new privimitive: iov_iter_revert() 



opposite to iov_iter_advance(); the caller is responsible for never
using it to move back past the initial position.

Cc: stable@vger.kernel.org
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent c02ed2e7

include/linux/uio.h

+5 −1
Original line number Diff line number Diff line
@@ -39,7 +39,10 @@ struct iov_iter { 
	};

	union {

		unsigned long nr_segs;

		struct {

			int idx;

			int start_idx;

		};

	};

};
@@ -81,6 +84,7 @@ unsigned long iov_shorten(struct iovec *iov, unsigned long nr_segs, size_t to); 
size_t iov_iter_copy_from_user_atomic(struct page *page,

		struct iov_iter *i, unsigned long offset, size_t bytes);

void iov_iter_advance(struct iov_iter *i, size_t bytes);

void iov_iter_revert(struct iov_iter *i, size_t bytes);

int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);

size_t iov_iter_single_seg_count(const struct iov_iter *i);

size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,

lib/iov_iter.c

+63 −0
Original line number Diff line number Diff line
@@ -786,6 +786,68 @@ void iov_iter_advance(struct iov_iter *i, size_t size) 
}

EXPORT_SYMBOL(iov_iter_advance);



void iov_iter_revert(struct iov_iter *i, size_t unroll)

{

	if (!unroll)

		return;

	i->count += unroll;

	if (unlikely(i->type & ITER_PIPE)) {

		struct pipe_inode_info *pipe = i->pipe;

		int idx = i->idx;

		size_t off = i->iov_offset;

		while (1) {

			size_t n = off - pipe->bufs[idx].offset;

			if (unroll < n) {

				off -= (n - unroll);

				break;

			}

			unroll -= n;

			if (!unroll && idx == i->start_idx) {

				off = 0;

				break;

			}

			if (!idx--)

				idx = pipe->buffers - 1;

			off = pipe->bufs[idx].offset + pipe->bufs[idx].len;

		}

		i->iov_offset = off;

		i->idx = idx;

		pipe_truncate(i);

		return;

	}

	if (unroll <= i->iov_offset) {

		i->iov_offset -= unroll;

		return;

	}

	unroll -= i->iov_offset;

	if (i->type & ITER_BVEC) {

		const struct bio_vec *bvec = i->bvec;

		while (1) {

			size_t n = (--bvec)->bv_len;

			i->nr_segs++;

			if (unroll <= n) {

				i->bvec = bvec;

				i->iov_offset = n - unroll;

				return;

			}

			unroll -= n;

		}

	} else { /* same logics for iovec and kvec */

		const struct iovec *iov = i->iov;

		while (1) {

			size_t n = (--iov)->iov_len;

			i->nr_segs++;

			if (unroll <= n) {

				i->iov = iov;

				i->iov_offset = n - unroll;

				return;

			}

			unroll -= n;

		}

	}

}

EXPORT_SYMBOL(iov_iter_revert);



/*

 * Return the count of just the current iov_iter segment.

 */
@@ -839,6 +901,7 @@ void iov_iter_pipe(struct iov_iter *i, int direction, 
	i->idx = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);

	i->iov_offset = 0;

	i->count = count;

	i->start_idx = i->idx;

}

EXPORT_SYMBOL(iov_iter_pipe);