Commit 9ea9ce04 authored by David Howells's avatar David Howells
Browse files

iov_iter: Add I/O discard iterator 



Add a new iterator, ITER_DISCARD, that can only be used in READ mode and
just discards any data copied to it.

This is useful in a network filesystem for discarding any unwanted data
sent by a server.

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
parent aa563d7b

include/linux/uio.h

+7 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ enum iter_type { 
	ITER_KVEC = 2,

	ITER_BVEC = 4,

	ITER_PIPE = 8,

	ITER_DISCARD = 16,

};



struct iov_iter {
@@ -72,6 +73,11 @@ static inline bool iov_iter_is_pipe(const struct iov_iter *i) 
	return iov_iter_type(i) == ITER_PIPE;

}



static inline bool iov_iter_is_discard(const struct iov_iter *i)

{

	return iov_iter_type(i) == ITER_DISCARD;

}



static inline unsigned char iov_iter_rw(const struct iov_iter *i)

{

	return i->type & (READ | WRITE);
@@ -220,6 +226,7 @@ void iov_iter_bvec(struct iov_iter *i, unsigned int direction, const struct bio_ 
			unsigned long nr_segs, size_t count);

void iov_iter_pipe(struct iov_iter *i, unsigned int direction, struct pipe_inode_info *pipe,

			size_t count);

void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count);

ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages,

			size_t maxsize, unsigned maxpages, size_t *start);

ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, struct page ***pages,

lib/iov_iter.c

+48 −7
Original line number Diff line number Diff line
@@ -83,6 +83,7 @@ 
			const struct kvec *kvec;		\

			struct kvec v;				\

			iterate_kvec(i, n, v, kvec, skip, (K))	\

		} else if (unlikely(i->type & ITER_DISCARD)) {	\

		} else {					\

			const struct iovec *iov;		\

			struct iovec v;				\
@@ -114,6 +115,8 @@ 
			}					\

			i->nr_segs -= kvec - i->kvec;		\

			i->kvec = kvec;				\

		} else if (unlikely(i->type & ITER_DISCARD)) {	\

			skip += n;				\

		} else {					\

			const struct iovec *iov;		\

			struct iovec v;				\
@@ -838,7 +841,9 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes, 
		size_t wanted = copy_to_iter(kaddr + offset, bytes, i);

		kunmap_atomic(kaddr);

		return wanted;

	} else if (likely(!iov_iter_is_pipe(i)))

	} else if (unlikely(iov_iter_is_discard(i)))

		return bytes;

	else if (likely(!iov_iter_is_pipe(i)))

		return copy_page_to_iter_iovec(page, offset, bytes, i);

	else

		return copy_page_to_iter_pipe(page, offset, bytes, i);
@@ -850,7 +855,7 @@ size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes, 
{

	if (unlikely(!page_copy_sane(page, offset, bytes)))

		return 0;

	if (unlikely(iov_iter_is_pipe(i))) {

	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {

		WARN_ON(1);

		return 0;

	}
@@ -910,7 +915,7 @@ size_t iov_iter_copy_from_user_atomic(struct page *page, 
		kunmap_atomic(kaddr);

		return 0;

	}

	if (unlikely(iov_iter_is_pipe(i))) {

	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {

		kunmap_atomic(kaddr);

		WARN_ON(1);

		return 0;
@@ -978,6 +983,10 @@ void iov_iter_advance(struct iov_iter *i, size_t size) 
		pipe_advance(i, size);

		return;

	}

	if (unlikely(iov_iter_is_discard(i))) {

		i->count -= size;

		return;

	}

	iterate_and_advance(i, size, v, 0, 0, 0)

}

EXPORT_SYMBOL(iov_iter_advance);
@@ -1013,6 +1022,8 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll) 
		pipe_truncate(i);

		return;

	}

	if (unlikely(iov_iter_is_discard(i)))

		return;

	if (unroll <= i->iov_offset) {

		i->iov_offset -= unroll;

		return;
@@ -1055,6 +1066,8 @@ size_t iov_iter_single_seg_count(const struct iov_iter *i) 
		return i->count;	// it is a silly place, anyway

	if (i->nr_segs == 1)

		return i->count;

	if (unlikely(iov_iter_is_discard(i)))

		return i->count;

	else if (iov_iter_is_bvec(i))

		return min(i->count, i->bvec->bv_len - i->iov_offset);

	else
@@ -1103,6 +1116,24 @@ void iov_iter_pipe(struct iov_iter *i, unsigned int direction, 
}

EXPORT_SYMBOL(iov_iter_pipe);



/**

 * iov_iter_discard - Initialise an I/O iterator that discards data

 * @i: The iterator to initialise.

 * @direction: The direction of the transfer.

 * @count: The size of the I/O buffer in bytes.

 *

 * Set up an I/O iterator that just discards everything that's written to it.

 * It's only available as a READ iterator.

 */

void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)

{

	BUG_ON(direction != READ);

	i->type = ITER_DISCARD | READ;

	i->count = count;

	i->iov_offset = 0;

}

EXPORT_SYMBOL(iov_iter_discard);



unsigned long iov_iter_alignment(const struct iov_iter *i)

{

	unsigned long res = 0;
@@ -1127,7 +1158,7 @@ unsigned long iov_iter_gap_alignment(const struct iov_iter *i) 
	unsigned long res = 0;

	size_t size = i->count;



	if (unlikely(iov_iter_is_pipe(i))) {

	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {

		WARN_ON(1);

		return ~0U;

	}
@@ -1197,6 +1228,9 @@ ssize_t iov_iter_get_pages(struct iov_iter *i, 


	if (unlikely(iov_iter_is_pipe(i)))

		return pipe_get_pages(i, pages, maxsize, maxpages, start);

	if (unlikely(iov_iter_is_discard(i)))

		return -EFAULT;



	iterate_all_kinds(i, maxsize, v, ({

		unsigned long addr = (unsigned long)v.iov_base;

		size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
@@ -1274,6 +1308,9 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, 


	if (unlikely(iov_iter_is_pipe(i)))

		return pipe_get_pages_alloc(i, pages, maxsize, start);

	if (unlikely(iov_iter_is_discard(i)))

		return -EFAULT;



	iterate_all_kinds(i, maxsize, v, ({

		unsigned long addr = (unsigned long)v.iov_base;

		size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
@@ -1315,7 +1352,7 @@ size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum, 
	__wsum sum, next;

	size_t off = 0;

	sum = *csum;

	if (unlikely(iov_iter_is_pipe(i))) {

	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {

		WARN_ON(1);

		return 0;

	}
@@ -1357,7 +1394,7 @@ bool csum_and_copy_from_iter_full(void *addr, size_t bytes, __wsum *csum, 
	__wsum sum, next;

	size_t off = 0;

	sum = *csum;

	if (unlikely(iov_iter_is_pipe(i))) {

	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {

		WARN_ON(1);

		return false;

	}
@@ -1402,7 +1439,7 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, __wsum *csum, 
	__wsum sum, next;

	size_t off = 0;

	sum = *csum;

	if (unlikely(iov_iter_is_pipe(i))) {

	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {

		WARN_ON(1);	/* for now */

		return 0;

	}
@@ -1444,6 +1481,8 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages) 


	if (!size)

		return 0;

	if (unlikely(iov_iter_is_discard(i)))

		return 0;



	if (unlikely(iov_iter_is_pipe(i))) {

		struct pipe_inode_info *pipe = i->pipe;
@@ -1487,6 +1526,8 @@ const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags) 
		WARN_ON(1);

		return NULL;

	}

	if (unlikely(iov_iter_is_discard(new)))

		return NULL;

	if (iov_iter_is_bvec(new))

		return new->bvec = kmemdup(new->bvec,

				    new->nr_segs * sizeof(struct bio_vec),