Re: [PATCH v6] io_uring/register: add IORING_REGISTER_CLONE_FILES opcode

[Harshal Chavan]

>> +     file = io_slot_file(src_node);
>> +     get_file(file);
>> +     io_fixed_file_set(dst_node, file);

> don't you need to copy the src_node->tag here as well?

Yes, sorry for the silly mistakes, thanks for catching this!

> I didn't get a chance to run it yet, sorry.  I'd suggest you wait for
> Jens feedback before pushing the v7 too, so you don't need to keep
> iterating drop by drop :)

Okay, Yes I will wait for feedback from Jens and send the changes together
Thanks for the review.

Regards,
Harshal Chavan

On Fri, Jun 26, 2026 at 2:03 AM Gabriel Krisman Bertazi <krisman@xxxxxxx> wrote:
>
> Harshal Chavan <harshal24.chavan@xxxxxxxxx> writes:
>
> > Currently, if an application wants to duplicate registered file
> > descriptors from one io_uring instance to another, it must manually
> > unregister and re-register them, incurring unnecessary overhead.
> >
> > Add IORING_REGISTER_CLONE_FILES to allow direct cloning of the file
> > table from a source ring to a destination ring. This implementation
> > strictly mirrors the io_clone_buffers UAPI, supporting partial offsets
> > and the IORING_REGISTER_DST_REPLACE flag.
> >
> > To ensure lock synchronization safety, destination nodes are strictly
> > allocated as new, private io_rsrc_nodes rather than sharing references
> > across rings.
> >
> > Signed-off-by: Harshal Chavan <harshal24.chavan@xxxxxxxxx>
> >
> > ---
> > Sorry for the noise on the previous email! I accidentally sent the patch
> > before running checkpatch and missed a whitespace error. This v6 corrects it.
> >
> > v6:
> >   - Fixed trailing whitespace checkpatch error.
> > v5:
> >   - Added missing spacing in comment (Gabriel).
> >   - Removed ctx->user and mm_account checks (Gabriel).
> >   - Used !! for boolean conversion (Gabriel).
> >   - Moved mutex_unlock unconditionally above the out label (Gabriel).
> >   - liburing implementation and tests: https://github.com/axboe/liburing/pull/1606
> > v4:
> >   - Updated Signed-off-by to use real name and moved above the scissors line (Greg KH).
> > v3:
> >   - Rewrote the cloning loop to allocate private destination nodes via io_rsrc_node_alloc to fix non-atomic ref lock synchronization (Jens).
> >   - Maintained partial offset/copy support to mirror io_clone_buffers UAPI (Jens).
> >   - Gated the replacement free check on ctx->file_table.data.nr (Gabriel).
> >   - Prevented self-cloning by checking ctx == src_ctx (Gabriel).
> >   - Removed submitter_task check to allow cross-thread pooling setups (Gabriel).
> > v2:
> >   - Dropped unrelated whitespace formatting changes from v1
>
> > +static int io_clone_file_node(struct io_ring_ctx *ctx,
> > +                           struct io_rsrc_node *src_node,
> > +                           int dst_index,
> > +                           struct io_file_table *new_table)
> > +{
> > +     struct io_rsrc_node *dst_node;
> > +     struct file *file;
> > +
> > +     dst_node = io_rsrc_node_alloc(ctx, IORING_RSRC_FILE);
> > +     if (!dst_node)
> > +             return -ENOMEM;
> > +
> > +     file = io_slot_file(src_node);
> > +     get_file(file);
> > +     io_fixed_file_set(dst_node, file);
>
> don't you need to copy the src_node->tag here as well?
>
> I didn't get a chance to run it yet, sorry.  I'd suggest you wait for
> Jens feedback before pushing the v7 too, so you don't need to keep
> iterating drop by drop :)
>
> > +
> > +     new_table->data.nodes[dst_index] = dst_node;
> > +     io_file_bitmap_set(new_table, dst_index);
> > +
> > +     return 0;
> > +}
> > +
> > +static int io_clone_files(struct io_ring_ctx *ctx, struct io_ring_ctx *src_ctx,
> > +                       struct io_uring_clone_files *arg)
> > +{
> > +     struct io_file_table new_file_table;
> > +     unsigned int dst_nr = ctx->file_table.data.nr;
> > +     unsigned int src_nr = src_ctx->file_table.data.nr;
> > +     unsigned int new_nr, i;
> > +
> > +     lockdep_assert_held(&ctx->uring_lock);
> > +     lockdep_assert_held(&src_ctx->uring_lock);
> > +
> > +     if (dst_nr && !(arg->flags & IORING_REGISTER_DST_REPLACE))
> > +             return -EBUSY;
> > +
> > +     if (!src_nr)
> > +             return -ENXIO;
> > +
> > +     if (!arg->nr)
> > +             arg->nr = src_nr;
> > +     else if (arg->nr > src_nr)
> > +             return -EINVAL;
> > +
> > +     if (check_add_overflow(arg->src_off, arg->nr, &i) || i > src_nr)
> > +             return -EINVAL;
> > +     if (check_add_overflow(arg->dst_off, arg->nr, &i))
> > +             return -EINVAL;
> > +
> > +     new_nr = max(dst_nr, arg->dst_off + arg->nr);
> > +     if (new_nr > IORING_MAX_FIXED_FILES)
> > +             return -EINVAL;
> > +
> > +     memset(&new_file_table, 0, sizeof(new_file_table));
> > +     if (!io_alloc_file_tables(ctx, &new_file_table, new_nr))
> > +             return -ENOMEM;
> > +
> > +     /* Copy original nodes from before the cloned range */
> > +     for (i = 0; i < min(arg->dst_off, dst_nr); i++) {
> > +             struct io_rsrc_node *src_node = io_rsrc_node_lookup(&ctx->file_table.data, i);
> > +
> > +             if (!src_node)
> > +                     continue;
> > +             if (io_clone_file_node(ctx, src_node, i, &new_file_table))
> > +                     goto out;
> > +     }
> > +
> > +     /* Copy the actual cloned range from the source ring */
> > +     for (i = 0; i < arg->nr; i++) {
> > +             struct io_rsrc_node *src_node = io_rsrc_node_lookup(&src_ctx->file_table.data,
> > +                             arg->src_off + i);
> > +
> > +             if (!src_node)
> > +                     continue;
> > +             if (io_clone_file_node(ctx, src_node, arg->dst_off + i, &new_file_table))
> > +                     goto out;
> > +     }
> > +
> > +     /* Copy original nodes from after the cloned range */
> > +     for (i = arg->dst_off + arg->nr; i < dst_nr; i++) {
> > +             struct io_rsrc_node *src_node = io_rsrc_node_lookup(&ctx->file_table.data, i);
> > +
> > +             if (!src_node)
> > +                     continue;
> > +             if (io_clone_file_node(ctx, src_node, i, &new_file_table))
> > +                     goto out;
> > +     }
> > +
> > +     /* free the old file table if there is any data present */
> > +     if (dst_nr)
> > +             io_free_file_tables(ctx, &ctx->file_table);
> > +
> > +     WARN_ON_ONCE(ctx->file_table.data.nr);
> > +     ctx->file_table = new_file_table;
> > +     io_file_table_set_alloc_range(ctx, 0, ctx->file_table.data.nr);
> > +     return 0;
> > +
> > +out:
> > +     /* Error Path: Safely destroy whatever we partially built */
> > +     io_free_file_tables(ctx, &new_file_table);
> > +     return -ENOMEM;
> > +}
> > +
> > +int io_register_clone_files(struct io_ring_ctx *ctx, void __user *arg)
> > +{
> > +     struct io_uring_clone_files clone_arg;
> > +     struct io_ring_ctx *src_ctx;
> > +     bool registered_src;
> > +     struct file *file;
> > +     int ret;
> > +
> > +     if (copy_from_user(&clone_arg, arg, sizeof(clone_arg)))
> > +             return -EFAULT;
> > +     if (clone_arg.flags &
> > +         ~(IORING_REGISTER_SRC_REGISTERED | IORING_REGISTER_DST_REPLACE))
> > +             return -EINVAL;
> > +
> > +     if (memchr_inv(clone_arg.pad, 0, sizeof(clone_arg.pad)))
> > +             return -EINVAL;
> > +
> > +     registered_src = !!(clone_arg.flags & IORING_REGISTER_SRC_REGISTERED);
> > +     file = io_uring_ctx_get_file(clone_arg.src_fd, registered_src);
> > +     if (IS_ERR(file))
> > +             return PTR_ERR(file);
> > +
> > +     src_ctx = file->private_data;
> > +     /* Same ring clone is not allowed */
> > +     if (src_ctx == ctx) {
> > +             ret = -EINVAL;
> > +             goto out;
> > +     }
> > +
> > +     mutex_unlock(&ctx->uring_lock);
> > +     lock_two_rings(ctx, src_ctx);
> > +
> > +     ret = io_clone_files(ctx, src_ctx, &clone_arg);
> > +
> > +     mutex_unlock(&src_ctx->uring_lock);
> > +
> > +out:
> > +     if (!registered_src)
> > +             fput(file);
> > +     return ret;
> > +}
> > +
> >  void io_vec_free(struct iou_vec *iv)
> >  {
> >       if (!iv->iovec)
> > diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
> > index 44e3386f7c1c..32f5c47c46af 100644
> > --- a/io_uring/rsrc.h
> > +++ b/io_uring/rsrc.h
> > @@ -75,6 +75,7 @@ int io_prep_reg_iovec(struct io_kiocb *req, struct iou_vec *iv,
> >                       const struct iovec __user *uvec, size_t uvec_segs);
> >
> >  int io_register_clone_buffers(struct io_ring_ctx *ctx, void __user *arg);
> > +int io_register_clone_files(struct io_ring_ctx *ctx, void __user *arg);
> >  int io_sqe_buffers_unregister(struct io_ring_ctx *ctx);
> >  int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
> >                           unsigned int nr_args, u64 __user *tags);
> > --
> > 2.54.0
> >
>
> --
> Gabriel Krisman Bertazi