Re: [PATCH bpf-next v4 2/5] bpf: Add dmabuf iterator

["T.J. Mercier" <tjmercier@google.com>]

On Thu, May 8, 2025 at 5:27 PM Song Liu <song@kernel.org> wrote:
>
> On Thu, May 8, 2025 at 11:20 AM T.J. Mercier <tjmercier@google.com> wrote:
> >
> > The dmabuf iterator traverses the list of all DMA buffers.
> >
> > DMA buffers are refcounted through their associated struct file. A
> > reference is taken on each buffer as the list is iterated to ensure each
> > buffer persists for the duration of the bpf program execution without
> > holding the list mutex.
> >
> > Signed-off-by: T.J. Mercier <tjmercier@google.com>
> > Reviewed-by: Christian König <christian.koenig@amd.com>
>
> Acked-by: Song Liu <song@kernel.org>
>
> With one nitpick below.

Thanks!

> > ---
> [...]
> > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> > index 8ff4add71f88..7af2ea839f58 100644
> > --- a/include/linux/dma-buf.h
> > +++ b/include/linux/dma-buf.h
> > @@ -634,4 +634,6 @@ int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map);
> >  void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map);
> >  int dma_buf_vmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map);
> >  void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map);
> > +struct dma_buf *dma_buf_iter_begin(void);
> > +struct dma_buf *dma_buf_iter_next(struct dma_buf *dmbuf);
> >  #endif /* __DMA_BUF_H__ */
> > diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> > index 70502f038b92..3a335c50e6e3 100644
> > --- a/kernel/bpf/Makefile
> > +++ b/kernel/bpf/Makefile
> > @@ -53,6 +53,9 @@ obj-$(CONFIG_BPF_SYSCALL) += relo_core.o
> >  obj-$(CONFIG_BPF_SYSCALL) += btf_iter.o
> >  obj-$(CONFIG_BPF_SYSCALL) += btf_relocate.o
> >  obj-$(CONFIG_BPF_SYSCALL) += kmem_cache_iter.o
> > +ifeq ($(CONFIG_DMA_SHARED_BUFFER),y)
> > +obj-$(CONFIG_BPF_SYSCALL) += dmabuf_iter.o
> > +endif
> >
> >  CFLAGS_REMOVE_percpu_freelist.o = $(CC_FLAGS_FTRACE)
> >  CFLAGS_REMOVE_bpf_lru_list.o = $(CC_FLAGS_FTRACE)
> > diff --git a/kernel/bpf/dmabuf_iter.c b/kernel/bpf/dmabuf_iter.c
> > new file mode 100644
> > index 000000000000..96b4ba7f0b2c
> > --- /dev/null
> > +++ b/kernel/bpf/dmabuf_iter.c
> > @@ -0,0 +1,102 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/* Copyright (c) 2025 Google LLC */
> > +#include <linux/bpf.h>
> > +#include <linux/btf_ids.h>
> > +#include <linux/dma-buf.h>
> > +#include <linux/kernel.h>
> > +#include <linux/seq_file.h>
> > +
> > +BTF_ID_LIST_SINGLE(bpf_dmabuf_btf_id, struct, dma_buf)
> > +DEFINE_BPF_ITER_FUNC(dmabuf, struct bpf_iter_meta *meta, struct dma_buf *dmabuf)
>
> nit: It is better to move these two lines later, to where they
> are about to be used.

I've moved them both to just before dmabuf_iter_init() farther down.