[PATCH v12 2/9] dma-buf: dma-heap: export declared functions

[John Stultz]

On Thu, Oct 2, 2025 at 12:47 AM Maxime Ripard <mripard at redhat.com> wrote:
> On Thu, Sep 11, 2025 at 03:49:43PM +0200, Jens Wiklander wrote:
> > Export the dma-buf heap functions to allow them to be used by the OP-TEE
> > driver. The OP-TEE driver wants to register and manage specific secure
> > DMA heaps with it.
> >
> > Reviewed-by: Sumit Garg <sumit.garg at oss.qualcomm.com>
> > Reviewed-by: T.J. Mercier <tjmercier at google.com>
> > Acked-by: Sumit Semwal <sumit.semwal at linaro.org>
> > Signed-off-by: Jens Wiklander <jens.wiklander at linaro.org>
> > ---
> >  drivers/dma-buf/dma-heap.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> > index 3cbe87d4a464..8ab49924f8b7 100644
> > --- a/drivers/dma-buf/dma-heap.c
> > +++ b/drivers/dma-buf/dma-heap.c
> > @@ -11,6 +11,7 @@
> >  #include <linux/dma-buf.h>
> >  #include <linux/dma-heap.h>
> >  #include <linux/err.h>
> > +#include <linux/export.h>
> >  #include <linux/list.h>
> >  #include <linux/nospec.h>
> >  #include <linux/syscalls.h>
> > @@ -202,6 +203,7 @@ void *dma_heap_get_drvdata(struct dma_heap *heap)
> >  {
> >       return heap->priv;
> >  }
> > +EXPORT_SYMBOL_NS_GPL(dma_heap_get_drvdata, "DMA_BUF_HEAP");
> >
> >  /**
> >   * dma_heap_get_name - get heap name
> > @@ -214,6 +216,7 @@ const char *dma_heap_get_name(struct dma_heap *heap)
> >  {
> >       return heap->name;
> >  }
> > +EXPORT_SYMBOL_NS_GPL(dma_heap_get_name, "DMA_BUF_HEAP");
> >
> >  /**
> >   * dma_heap_add - adds a heap to dmabuf heaps
> > @@ -303,6 +306,7 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
> >       kfree(heap);
> >       return err_ret;
> >  }
> > +EXPORT_SYMBOL_NS_GPL(dma_heap_add, "DMA_BUF_HEAP");
>
> It's not clear to me why we would need to export those symbols.
>
> As far as I know, heaps cannot be removed, and compiling them as module
> means that we would be able to remove them.
>
> Now, if we don't expect the users to be compiled as modules, then we
> don't need to export these symbols at all.
>
> Am I missing something?

For things like distro kernels (or in Android's case, the GKI),
there's a benefit for modules that can be loaded permanently (not
having a module_exit hook).
One doesn't have to bloat the base kernel image/memory usage for
everyone, while still not having to necessarily deal with
complications from module unloading issues.

thanks
-john