// 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();