Re: [PATCH v19 0/8] MR3103: server: Create and use a desktop shared mapping for GetCursorPos.

[Jinoh Kang (＠iamahuman)]

Jinoh Kang (@iamahuman) commented about server/mapping.c:
> - SHARED_WRITE_END;
> -
> - for (i = 0; i < session.object_count; i++)
> - {
> -
>    const session_obj_t *object = &session.shared->objects[i];
> -
>    SHARED_WRITE_BEGIN( object, session_obj_t )
> -
>    {
> -
>        shared->obj.invalid = 1;
> -
>    }
> -
>    SHARED_WRITE_END;
> - }
> -
> - munmap( (void *)session.shared, session_mapping->size );
> - release_object( session_mapping->fd );
> - session_mapping->size = size;
> - session_mapping->fd = fd;

Replacing the backing memory/fd of a mapping object is unprecedented and I'm afraid this might cause regressing due to existing assumptions on a mapping object.

Instead, I suggest that you remove `OBJ_PERMANENT` flag[^perma], unlink the existing mapping[^unlink], and call `create_mapping` to construct a new one.

This will also solve the query size race condition automatically.

[^perma]: This requires you to make `session_mapping` a reference: see the suggestion about `session_mapping = (struct mapping *)grab_object( &mapping->obj );`.
[^unlink]: See `unlink_named_object`.