[PATCH v3 02/10] iov_iter: add iterator type for dmabuf maps

Pavel Begunkov
2026-04-29T15:26:30Z

Introduce a new iterator type for dmabuf maps. The map in an opaque
object with internals and format specific to the subsystem / driver, and
only it can use that subsystem / driver for issuing IO. The task of the
middle layers is to pass the map / iterator further down, maybe doing
basic splitting and length checking. The iterator can only be used by
operations of the file the associated map was created for.

Suggested-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
include/linux/uio.h | 11 +++++++++++
lib/iov_iter.c | 29 +++++++++++++++++++++++------
2 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index a9bc5b3067e3..75051aed70de 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -12,6 +12,7 @@

struct page;
struct folio_queue;
+struct io_dmabuf_map;

typedef unsigned int __bitwise iov_iter_extraction_t;

@@ -29,6 +30,7 @@ enum iter_type {
ITER_FOLIOQ,
ITER_XARRAY,
ITER_DISCARD,
+ ITER_DMABUF_MAP,
};

#define ITER_SOURCE 1 // == WRITE
@@ -71,6 +73,7 @@ struct iov_iter {
const struct folio_queue *folioq;
struct xarray *xarray;
void __user *ubuf;
+ struct io_dmabuf_map *dmabuf_map;
};
size_t count;
};
@@ -155,6 +158,11 @@ static inline bool iov_iter_is_xarray(const struct iov_iter *i)
return iov_iter_type(i) == ITER_XARRAY;
}

+static inline bool iov_iter_is_dmabuf_map(const struct iov_iter *i)
+{
+ return iov_iter_type(i) == ITER_DMABUF_MAP;
+}
+
static inline unsigned char iov_iter_rw(const struct iov_iter *i)
{
return i->data_source ? WRITE : READ;
@@ -300,6 +308,9 @@ void iov_iter_folio_queue(struct iov_iter *i, unsigned int direction,
unsigned int first_slot, unsigned int offset, size_t count);
void iov_iter_xarray(struct iov_iter *i, unsigned int direction, struct xarray *xarray,
loff_t start, size_t count);
+void iov_iter_dmabuf_map(struct iov_iter *i, unsigned int direction,
+ struct io_dmabuf_map *map,
+ loff_t off, size_t count);
ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages,
size_t maxsize, unsigned maxpages, size_t *start);
ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i, struct page ***pages,
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 243662af1af7..e2253684b991 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -575,7 +575,8 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
{
if (unlikely(i->count < size))
size = i->count;
- if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i))) {
+ if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i)) ||
+ unlikely(iov_iter_is_dmabuf_map(i))) {
i->iov_offset += size;
i->count -= size;
} else if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i))) {
@@ -631,7 +632,8 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll)
return;
}
unroll -= i->iov_offset;
- if (iov_iter_is_xarray(i) || iter_is_ubuf(i)) {
+ if (iov_iter_is_xarray(i) || iter_is_ubuf(i) ||
+ iov_iter_is_dmabuf_map(i)) {
BUG(); /* We should never go beyond the start of the specified
* range since we might then be straying into pages that
* aren't pinned.
@@ -775,6 +777,20 @@ void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
}
EXPORT_SYMBOL(iov_iter_xarray);

+void iov_iter_dmabuf_map(struct iov_iter *i, unsigned int direction,
+ struct io_dmabuf_map *map,
+ loff_t off, size_t count)
+{
+ WARN_ON(direction & ~(READ | WRITE));
+ *i = (struct iov_iter){
+ .iter_type = ITER_DMABUF_MAP,
+ .data_source = direction,
+ .dmabuf_map = map,
+ .count = count,
+ .iov_offset = off,
+ };
+}
+
/**
* iov_iter_discard - Initialise an I/O iterator that discards data
* @i: The iterator to initialise.
@@ -841,7 +857,7 @@ static unsigned long iov_iter_alignment_bvec(const struct iov_iter *i)

unsigned long iov_iter_alignment(const struct iov_iter *i)
{
- if (likely(iter_is_ubuf(i))) {
+ if (likely(iter_is_ubuf(i)) || iov_iter_is_dmabuf_map(i)) {
size_t size = i->count;
if (size)
return ((unsigned long)i->ubuf + i->iov_offset) | size;
@@ -872,7 +888,7 @@ unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
size_t size = i->count;
unsigned k;

- if (iter_is_ubuf(i))
+ if (iter_is_ubuf(i) || iov_iter_is_dmabuf_map(i))
return 0;

if (WARN_ON(!iter_is_iovec(i)))
@@ -1469,11 +1485,12 @@ EXPORT_SYMBOL_GPL(import_ubuf);
void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
{
if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i) &&
- !iter_is_ubuf(i)) && !iov_iter_is_kvec(i))
+ !iter_is_ubuf(i) && !iov_iter_is_kvec(i) &&
+ !iov_iter_is_dmabuf_map(i)))
return;
i->iov_offset = state->iov_offset;
i->count = state->count;
- if (iter_is_ubuf(i))
+ if (iter_is_ubuf(i) || iov_iter_is_dmabuf_map(i))
return;
/*
* For the *vec iters, nr_segs + iov is constant - if we increment
--
2.53.0