[PATCH v3 09/10] io_uring/rsrc: extend buffer update

Pavel Begunkov
2026-04-29T15:27:04Z

We need to pass more information to buffer registration than we can fit
into a single struct iovec. This patch allows users to optionally pass
struct io_uring_regbuf_desc. Apart from having more space for future use
cases, it also introduces registration types.

Currently, the type can be either of IO_REGBUF_TYPE_UADDR, which mirrors
the iovec path, or IO_REGBUF_TYPE_EMPTY for leaving a buffer table slot
empty. The next patch introduces a dmabuf backed type, and can be useful
for other extensions like splicing a list of user addresses (i.e.
iovec[]), interoperability with zcrx, kernel allocated memory like was
brough up by Cristoph. Note, the type only represents a registration
option, which is distinct from how io_uring internally stores it.

The flags field is not used yet but always useful to have, e.g. we can
encode read-only / write-only restrictions using it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
include/uapi/linux/io_uring.h | 27 +++++++++++++-
io_uring/rsrc.c | 69 ++++++++++++++++++++++-------------
2 files changed, 69 insertions(+), 27 deletions(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 17ac1b785440..05c3fd078767 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -790,13 +790,38 @@ struct io_uring_rsrc_update {

struct io_uring_rsrc_update2 {
__u32 offset;
- __u32 resv;
+ __u32 flags;
__aligned_u64 data;
__aligned_u64 tags;
__u32 nr;
__u32 resv2;
};

+/* struct io_uring_rsrc_update2::flags */
+enum io_uring_rsrc_reg_flags {
+ /*
+ * Use the extended descriptor format for buffer updates,
+ * see struct io_uring_regbuf_desc
+ */
+ IORING_RSRC_UPDATE_EXTENDED = 1U << 1,
+};
+
+/* Buffer registration type, passed in struct io_uring_regbuf_desc::type */
+enum io_uring_regbuf_type {
+ IO_REGBUF_TYPE_EMPTY,
+ IO_REGBUF_TYPE_UADDR,
+
+ __IO_REGBUF_TYPE_MAX,
+};
+
+struct io_uring_regbuf_desc {
+ __u32 type; /* enum io_uring_regbuf_type */
+ __u32 flags;
+ __u64 size;
+ __u64 uaddr;
+ __u64 __resv[7];
+};
+
/* Skip updating fd indexes set to this value in the fd table */
#define IORING_REGISTER_FILES_SKIP (-2)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index ba00238941ed..f8696b01cb54 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -27,11 +27,6 @@ struct io_rsrc_update {
u32 offset;
};

-struct io_uring_regbuf_desc {
- __u64 uaddr;
- __u64 size;
-};
-
static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
struct io_uring_regbuf_desc *desc,
struct page **last_hpage);
@@ -46,9 +41,12 @@ static void io_iov_to_regbuf_desc(const struct iovec *iov,
struct io_uring_regbuf_desc *desc)
{
*desc = (struct io_uring_regbuf_desc) {
+ .type = IO_REGBUF_TYPE_UADDR,
.uaddr = (u64)iov->iov_base,
.size = iov->iov_len,
};
+ if (!desc->uaddr)
+ desc->type = IO_REGBUF_TYPE_EMPTY;
}

int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
@@ -236,6 +234,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
return -ENXIO;
if (up->offset + nr_args > ctx->file_table.data.nr)
return -EINVAL;
+ if (up->flags)
+ return -EINVAL;

for (done = 0; done < nr_args; done++) {
u64 tag = 0;
@@ -292,10 +292,9 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
struct io_uring_rsrc_update2 *up,
unsigned int nr_args)
{
+ bool extended = up->flags & IORING_RSRC_UPDATE_EXTENDED;
u64 __user *tags = u64_to_user_ptr(up->tags);
- struct iovec fast_iov, *iov;
struct page *last_hpage = NULL;
- struct iovec __user *uvec;
u64 user_data = up->data;
__u32 done;
int i, err;
@@ -304,29 +303,49 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
return -ENXIO;
if (up->offset + nr_args > ctx->buf_table.nr)
return -EINVAL;
+ if (up->flags & ~IORING_RSRC_UPDATE_EXTENDED)
+ return -EINVAL;

for (done = 0; done < nr_args; done++) {
struct io_uring_regbuf_desc desc;
struct io_rsrc_node *node;
u64 tag = 0;

- uvec = u64_to_user_ptr(user_data);
- iov = iovec_from_user(uvec, 1, 1, &fast_iov, io_is_compat(ctx));
- if (IS_ERR(iov)) {
- err = PTR_ERR(iov);
- break;
- }
if (tags && copy_from_user(&tag, &tags[done], sizeof(tag))) {
err = -EFAULT;
break;
}

- io_iov_to_regbuf_desc(iov, &desc);
+ if (extended) {
+ if (copy_from_user(&desc, u64_to_user_ptr(user_data),
+ sizeof(desc))) {
+ err = -EFAULT;
+ break;
+ }
+ user_data += sizeof(desc);
+ } else {
+ struct iovec __user *uvec = u64_to_user_ptr(user_data);
+ struct iovec fast_iov, *iov;
+
+ if (io_is_compat(ctx))
+ user_data += sizeof(struct compat_iovec);
+ else
+ user_data += sizeof(struct iovec);
+
+ iov = iovec_from_user(uvec, 1, 1, &fast_iov, io_is_compat(ctx));
+ if (IS_ERR(iov)) {
+ err = PTR_ERR(iov);
+ break;
+ }
+ io_iov_to_regbuf_desc(iov, &desc);
+ }
+
node = io_sqe_buffer_register(ctx, &desc, &last_hpage);
if (IS_ERR(node)) {
err = PTR_ERR(node);
break;
}
+
if (tag) {
if (!node) {
err = -EINVAL;
@@ -337,10 +356,6 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
i = array_index_nospec(up->offset + done, ctx->buf_table.nr);
io_reset_rsrc_node(ctx, &ctx->buf_table, i);
ctx->buf_table.nodes[i] = node;
- if (io_is_compat(ctx))
- user_data += sizeof(struct compat_iovec);
- else
- user_data += sizeof(struct iovec);
}
return done ? done : err;
}
@@ -375,7 +390,7 @@ int io_register_files_update(struct io_ring_ctx *ctx, void __user *arg,
memset(&up, 0, sizeof(up));
if (copy_from_user(&up, arg, sizeof(struct io_uring_rsrc_update)))
return -EFAULT;
- if (up.resv || up.resv2)
+ if (up.resv2)
return -EINVAL;
return __io_register_rsrc_update(ctx, IORING_RSRC_FILE, &up, nr_args);
}
@@ -389,7 +404,7 @@ int io_register_rsrc_update(struct io_ring_ctx *ctx, void __user *arg,
return -EINVAL;
if (copy_from_user(&up, arg, sizeof(up)))
return -EFAULT;
- if (!up.nr || up.resv || up.resv2)
+ if (!up.nr || up.resv2)
return -EINVAL;
return __io_register_rsrc_update(ctx, type, &up, up.nr);
}
@@ -489,12 +504,9 @@ int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
struct io_uring_rsrc_update2 up2;
int ret;

+ memset(&up2, 0, sizeof(up2));
up2.offset = up->offset;
up2.data = up->arg;
- up2.nr = 0;
- up2.tags = 0;
- up2.resv = 0;
- up2.resv2 = 0;

if (up->offset == IORING_FILE_INDEX_ALLOC) {
ret = io_files_update_with_index_alloc(req, issue_flags);
@@ -791,8 +803,13 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
struct io_imu_folio_data data;
bool coalesced = false;

- if (!uaddr) {
- if (size)
+ if (desc->type >= __IO_REGBUF_TYPE_MAX)
+ return ERR_PTR(-EINVAL);
+ if (!mem_is_zero(&desc->__resv, sizeof(desc->__resv)))
+ return ERR_PTR(-EINVAL);
+
+ if (desc->type == IO_REGBUF_TYPE_EMPTY) {
+ if (uaddr || size)
return ERR_PTR(-EFAULT);
/* remove the buffer without installing a new one */
return NULL;
--
2.53.0