dmabuf_iter.c

// 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>

struct dmabuf_iter_priv {
	/*
	 * If this pointer is non-NULL, the buffer's refcount is elevated to
	 * prevent destruction between stop/start. If reading is not resumed and
	 * start is never called again, then dmabuf_iter_seq_fini drops the
	 * reference when the iterator is released.
	 */
	struct dma_buf *dmabuf;
};

static void *dmabuf_iter_seq_start(struct seq_file *seq, loff_t *pos)
{
	struct dmabuf_iter_priv *p = seq->private;

	if (*pos) {
		struct dma_buf *dmabuf = p->dmabuf;

		if (!dmabuf)
			return NULL;

		/*
		 * Always resume from where we stopped, regardless of the value
		 * of pos.
		 */
		p->dmabuf = NULL;
		return dmabuf;
	}

	return dma_buf_iter_begin();
}

static void *dmabuf_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
	struct dma_buf *dmabuf = v;

	++*pos;

	return dma_buf_iter_next(dmabuf);
}

struct bpf_iter__dmabuf {
	__bpf_md_ptr(struct bpf_iter_meta *, meta);
	__bpf_md_ptr(struct dma_buf *, dmabuf);
};

static int __dmabuf_seq_show(struct seq_file *seq, void *v, bool in_stop)
{
	struct bpf_iter_meta meta = {
		.seq = seq,
	};
	struct bpf_iter__dmabuf ctx = {
		.meta = &meta,
		.dmabuf = v,
	};
	struct bpf_prog *prog = bpf_iter_get_info(&meta, in_stop);

	if (prog)
		return bpf_iter_run_prog(prog, &ctx);

	return 0;
}

static int dmabuf_iter_seq_show(struct seq_file *seq, void *v)
{
	return __dmabuf_seq_show(seq, v, false);
}

static void dmabuf_iter_seq_stop(struct seq_file *seq, void *v)
{
	struct dma_buf *dmabuf = v;

	if (dmabuf) {
		struct dmabuf_iter_priv *p = seq->private;

		p->dmabuf = dmabuf;
	}
}

static const struct seq_operations dmabuf_iter_seq_ops = {
	.start	= dmabuf_iter_seq_start,
	.next	= dmabuf_iter_seq_next,
	.stop	= dmabuf_iter_seq_stop,
	.show	= dmabuf_iter_seq_show,
};

static void bpf_iter_dmabuf_show_fdinfo(const struct bpf_iter_aux_info *aux,
					struct seq_file *seq)
{
	seq_puts(seq, "dmabuf iter\n");
}

static int dmabuf_iter_seq_init(void *priv, struct bpf_iter_aux_info *aux)
{
	struct dmabuf_iter_priv *p = (struct dmabuf_iter_priv *)priv;

	p->dmabuf = NULL;
	return 0;
}

static void dmabuf_iter_seq_fini(void *priv)
{
	struct dmabuf_iter_priv *p = (struct dmabuf_iter_priv *)priv;

	if (p->dmabuf)
		dma_buf_put(p->dmabuf);
}

static const struct bpf_iter_seq_info dmabuf_iter_seq_info = {
	.seq_ops		= &dmabuf_iter_seq_ops,
	.init_seq_private	= dmabuf_iter_seq_init,
	.fini_seq_private	= dmabuf_iter_seq_fini,
	.seq_priv_size		= sizeof(struct dmabuf_iter_priv),
};

static struct bpf_iter_reg bpf_dmabuf_reg_info = {
	.target			= "dmabuf",
	.feature                = BPF_ITER_RESCHED,
	.show_fdinfo		= bpf_iter_dmabuf_show_fdinfo,
	.ctx_arg_info_size	= 1,
	.ctx_arg_info		= {
		{ offsetof(struct bpf_iter__dmabuf, dmabuf),
		  PTR_TO_BTF_ID_OR_NULL },
	},
	.seq_info		= &dmabuf_iter_seq_info,
};

DEFINE_BPF_ITER_FUNC(dmabuf, struct bpf_iter_meta *meta, struct dma_buf *dmabuf)
BTF_ID_LIST_SINGLE(bpf_dmabuf_btf_id, struct, dma_buf)

static int __init dmabuf_iter_init(void)
{
	bpf_dmabuf_reg_info.ctx_arg_info[0].btf_id = bpf_dmabuf_btf_id[0];
	return bpf_iter_reg_target(&bpf_dmabuf_reg_info);
}

late_initcall(dmabuf_iter_init);

struct bpf_iter_dmabuf {
	/*
	 * opaque iterator state; having __u64 here allows to preserve correct
	 * alignment requirements in vmlinux.h, generated from BTF
	 */
	__u64 __opaque[1];
} __aligned(8);

/* Non-opaque version of bpf_iter_dmabuf */
struct bpf_iter_dmabuf_kern {
	struct dma_buf *dmabuf;
} __aligned(8);

__bpf_kfunc_start_defs();

__bpf_kfunc int bpf_iter_dmabuf_new(struct bpf_iter_dmabuf *it)
{
	struct bpf_iter_dmabuf_kern *kit = (void *)it;

	BUILD_BUG_ON(sizeof(*kit) > sizeof(*it));
	BUILD_BUG_ON(__alignof__(*kit) != __alignof__(*it));

	kit->dmabuf = NULL;
	return 0;
}

__bpf_kfunc struct dma_buf *bpf_iter_dmabuf_next(struct bpf_iter_dmabuf *it)
{
	struct bpf_iter_dmabuf_kern *kit = (void *)it;

	if (kit->dmabuf)
		kit->dmabuf = dma_buf_iter_next(kit->dmabuf);
	else
		kit->dmabuf = dma_buf_iter_begin();

	return kit->dmabuf;
}

__bpf_kfunc void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it)
{
	struct bpf_iter_dmabuf_kern *kit = (void *)it;

	if (kit->dmabuf)
		dma_buf_put(kit->dmabuf);
}

__bpf_kfunc_end_defs();